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DIFFERENT ASPECTS
RELATED TO LUTING FIBER POSTS
Ivana Radovi�
1
UNIVERSITY OF SIENA
School of Dental Medicine
PhD PROGRAM:
“DENTAL MATERIALS AND THEIR CLINICAL
APPLICATIONS”
PhD THESIS OF:
Ivana Radovi�_________________________________________________
TITLE:
Different aspects related to luting fiber posts
Academic Year 2008/09
2
December 11th 2009
Siena, Italy
Committee:
Promoter Prof. Marco Ferrari
Co-Promoter Prof. Zoran R. Vuli�evi�
Prof. Leopoldo Forner Navarro
Prof. Andrea Borracchini
Prof. Cecilia Goracci
Prof. Lorenzo Breschi
Prof. Simone Grandini
TITLE:
Different aspects related to luting fiber posts
CANDIDATE
Ivana Radovi�
3
Table of contents
Chapter 1: Introduction _______________________________ 5�
1.1. Fiber posts – general facts __________________________________ 5�
Chapter 2: Treatments of fiber post surface _____________ 23�
2.1. The effect of sandblasting on adhesion of a dual-cured resin composite
to methacrylic fiber posts: microtensile bond strength and SEM evaluation
__________________________________________________________ 23�
2.2. Accelerated aging of adhesive-mediated fiber post-resin composite
bonds: a modeling approach ___________________________________ 44�
2.3. Coupling of composite resin cements to quartz fiber post: a
comparison of industrial and “chair-side” treatments of the post surface _ 64�
Chapter 3: Selection of resin cement for fiber post
cementation ________________________________________ 91�
3.1. Self-adhesive resin cements: a literature review ________________ 91�
3.2. Evaluation of the adhesion of fiber posts cemented using different
adhesive approaches ________________________________________ 118�
Chapter 4: Light transmission through fiber post ________ 144�
4.1. Light transmission through fiber post: The effect on adhesion, elastic
modulus and hardness of dual-cure resin cement __________________ 144�
Summary _________________________________________ 169�
Conclusions _______________________________________ 172�
4
Sommario e conclusioni _____________________________ 173�
Sommaire et conclusions ____________________________ 178�
Zusammenfassung und schlussfolgerungen _____________ 184�
Sažetak i zaklju�ci __________________________________ 189�
Complete list of references ___________________________ 195�
Curriculum vitae ___________________________________ 218�
Acknowledgements _________________________________ 226�
5
Chapter 1: Introduction
1.1. Fiber posts – general facts
Fiber reinforced composite posts are the newest in line of endodontic posts
that are available to clinicians today. They have been used for more than
twenty years (Duret et al. 1990). The first posts were made of carbon fibers.
Even though carbon fiber posts demonstrated favorable clinical behavior
(Fredriksson et al. 1998), nowadays they have been almost entirely replaced
by quartz and glass fiber posts, primarily for esthetic reasons. Beside fibers,
posts may contain epoxy or methacrylate resin.
The most widely known feature of fiber posts is their elasticity, which
is similar to dentin and composite resins (Asmussen et al. 1999). The
modulus of elasticity of cast, titanium and ceramic posts is several times
higher which implies that these posts are much more rigid than fiber posts
(Table). Due to favorable elasticity, stress distribution during clinical
function is uniform and spreads along the entire root. On the other side, when
rigid metallic posts are used, stress concentrates in isolated points and the
risk of root fracture is much higher (Figure).
This feature may be particularly important and beneficial in pediatric
dentistry, especially in cases when teeth have to be restored following
apexification procedures, since in such short roots with extremely thin walls,
fiber posts may prevent root fractures that are otherwise quite common
(Katebzadeh et al. 1998). Even in fully developed roots, young patients’ teeth
still have fairly wide root canals that may benefit too from the placement of
fiber post instead of much more rigid metallic posts that some time ago used
to be the only option. Good clinical performance of endodontically treated
6
teeth restored with fiber posts and direct composite restorations has been
reported (Grandini et al. 2005c), which is also of importance for pediatric
dentistry. Besides favorable mechanical properties, fiber posts provide a fine
esthetic base for direct composite restorations or full ceramic crowns (Ferrari
2008).
Table: Modulus of elasticity of dentin and different post materials (Tay and
Pashley 2007)
Material Modulus of elasticity [GPa] Dentin 14 – 19 Fiber posts 18 – 22 Ceramic posts (ZrO2) 96 Titanium posts 120 Cast posts 200
Figure: Fiber posts provide balanced stress distribution along the root (left),
whereas considerably stiffer metallic posts may cause stress concentration in
isolated points (right).
7
It was noted long time ago that endodontically treated teeth are
weaker than vital teeth. It is now known that the main reason for this is the
loss of crown tissue due to decay or trauma (Reeh et al. 1989). Further
weakening takes place when access cavity is prepared (Panitvisai and Messer
1995). Additionally, following pulp removal, the protective feed-back
mechanism that the pulp provides is lost, and roots are prone to fractures
(Randow and Glantz 1986).
Even though a strengthening effect is often needed when restoring
endodontically treated teeth, research has clearly shown that metallic posts
cannot fulfill this task (Guzy and Nicholls 1979; Trope et al. 1985).
Therefore, the main indication for post placement is the need for additional
retention for crown restoration (Schwartz and Robbins 2004). This applies to
all endodontic posts, including fiber posts. However, knowing the favorable
fiber post properties that provide well balanced stress distribution and root
fracture prevention, it makes sense to assume that adhesively cemented fiber
posts may also strengthen teeth to a certain extent, apart from providing
additional retention. Indeed, it was reported that strengthening effect is
present immediately after adhesive post cementation (Saupe et al. 1996;
Mannocci et al. 1999). Nevertheless, it is believed that this strengthening
effect is lost during function (Schwartz and Robbins 2004). Therefore, in
order to better understand the strengthening effect and its duration, it was
recommended to include simulations of clinical function into studies that
investigate this topic (Schwartz and Robbins 2004).
Apart from the usual indications, fiber posts may be extremely useful
in traumatology, for reattaching fractured crown fragments following
endodontic treatment (Durkan et al. 2008), or in case of complicated crown-
root fractures (Fidel et al. 2006). This approach follows the general trend of
minimal intervention dentistry (Mount and Ngo 2000), and may provide
8
functional and economical treatments regardless of patient’s age. However,
in pediatric dentistry, it may be particularly important, as it enables to
postpone the crown placement and preserve the integrity of the epithelial
junction in a young patient. Orthodontic extrusion may also be performed
with an aid of fiber post after a traumatic injury, if indicated (Yuzugullu et al.
2008).
Different shapes of fiber posts are available: parallel, tapered, or posts
may have additional macro retentive grooves. Similar survival rates were
reported for parallel and tapered fiber posts in a recent clinical study (Signore
et al. 2009). However, greater removal of root canal dentin is usually
inevitable in order to fit in a parallel shaped post. For this reason, tapered
posts are generally recommended, especially in teeth with thin roots and
delicate morphology, as tapered posts respect root canal's anatomy and
require only minimal removal of root canal dentin (Schwartz and Robbins
2004).
Even though all fiber posts consist of fibers and matrix, they don’t all
have similar mechanical properties. This was clearly demonstrated when
posts were subjected to cyclic loading of 2 million cycles that roughly
simulated four years of clinical function (Grandini et al. 2005b). Only one
post was able to withstand this loading while the others fractured at less than
2 million cycles. The authors stated that a slightly different design might
have provided findings of higher clinical relevance. Nevertheless, from the
two clinical studies by Naumann (Naumann et al. 2005a; Naumann et al.
2005b), a correlation may be observed between in vitro findings and actual
clinical behavior of some posts. Fiber posts that exhibited poor mechanical
properties in the study by Grandini et al. were reported to fail by post fracture
in the two clinical studies (Naumann et al. 2005a; Naumann et al. 2005b). On
the other side, when post with superior mechanical properties was used,
9
fractures of the posts were never reported to be a cause of clinical failure
(Monticelli et al. 2003; Cagidiaco et al. 2007; Cagidiaco et al. 2008a).
Several factors are believed to influence the success of fiber post
cementation and fiber post-retained restorations. It is often recommended to
avoid eugenol based sealers, due to risk that remnants of eugenol in dentinal
tubules may interfere with complete polymerization of resin cements and
adhesives. Literature is not consistent on this topic. Kurtz et al. have shown
that post retention is not impaired with eugenol based sealers (Kurtz et al.
2003). On the other side, lower fiber post retention in roots treated with
eugenol based sealers was also reported (Baldissara et al. 2006). Etch-and-
rinse adhesives may attain higher adhesion to eugenol contaminated dentine
surfaces than self-etching adhesives (Carvalho et al. 2007). This was
explained by the self-etching adhesives’ mechanism of action, which is based
on incorporation of the eugenol containing smear layer into the hybrid layer.
Conversely, phosphoric acid removes the smear layer, and hence it is much
more effective in removing the remnants of eugenol from the dentine surface.
For this reason, etch-and-rinse adhesive system may be preferable for fiber
post cementation in roots treated with eugenol based endodontic sealers
(Ferrari 2008).
There are many clinical studies that have shown that failures happen
more often when crown destruction is extensive. Therefore, clinically every
effort should be made to preserve as much coronal tissue as possible
(Cagidiaco et al. 2008b). More importantly, in case of crown placement,
literature is in agreement that preparation of a 2mm-high 1mm-thick ferrule
will give the restoration the highest chances for long lasting successful
clinical function (Stankiewicz and Wilson 2002). It was also demonstrated
that even the preparation of a non-uniform ferrule, which is clinically often
10
the only option, provides higher fracture resistance than no ferrule at all (Tan
et al. 2005).
During fiber post cementation, it is recommended to keep the resin
cement layer as thin as possible. Even though one study showed that cement
layer does not influence fiber post retention (Perez et al. 2006), the
recommendation remains. As resin cements are formulated to be used in thin
films, their mechanical properties allow only a thin layer around the post, in
order to provide the most favorable stress distribution along the root. In case
of oval canals, in which a circular post cannot fit perfectly, since recently
small, so called accessory posts are available that may be placed in addition
to the main post (Porciani et al. 2008). The placement of accessory posts can
be roughly compared to lateral gutta-percha condensation, with an aim to
reduce the amount of resin cement as much as possible. For the same purpose
oval or anatomic posts (Grandini et al. 2005a) may be used, too.
The standard rules for endodontic post length in root canal apply for
fiber posts too. The most important two rules to follow are to leave 4-5 mm
of gutta-percha and sealer apically in order to prevent apical microleakage,
and to assure that the ratio between the root part of the post and the crown is
at least one to one or more whenever possible (Schwartz and Robbins 2004).
Clinical studies of fiber posts have shown good clinical performance
of this treatment option. Nevertheless, it was noted that if the treatment fails,
it usually does due to debonding of the post (Cagidiaco et al. 2008b). For this
reason, adequate attention needs to be given to both of the interfaces that
form when post is cemented: fiber post-cement interface and cement-root
dentin interface. It was recently assumed that the amount of light
transmission through the post may affect both these interfaces (Goracci et al.
2008, Ferrari 2008). Fiber post-cement interface may be influenced through
different treatments of the post surface, whereas cement-root dentin interface
11
is primarily affected by the type of resin cement/adhesive approach used.
Therefore, fiber post surface treatment, resin cement selection and light
transmission through the post were the three aspects of post cementation that
this thesis focused on. Studies assessing each aspect are presented in
Chapters 2, 3 and 4, respectively.
Fiber post surface treatment
It was reported that the fiber post-cement interface is one of the levels where
a debonding failure can occur (Perdigao et al. 2006), and a number of
investigations focused on improving the adhesion at this interface. Coupling
between fiber posts and resin cements may be influenced by post surface
treatments. Various post surface treatments have been investigated so far. It
appears from the current literature that the majority of fiber posts benefit
from some kind of surface treatment, though the best treatment is not the
same for every post (Monticelli et al. 2008). Fiber post surface treatment
procedures fall within three categories (Monticelli et al. 2008):
1. treatments that result in chemical bonding between composite and
post (coating with primer solutions)
2. treatments that roughen the surface (sandblasting and etching)
3. treatments that combine both a micromechanical and chemical
component, either by a combination of the two above-mentioned
treatments or by the use of specific systems (e.g. Co-Jet®)
Chapter 2 of this thesis presents three studies that investigated various
treatments of fiber post surface. In order to determine the influence of surface
treatments to fiber post adhesion, post-composite microtensile bond strength
tests (Goracci et al. 2005a) and SEM investigations were performed.
12
Resin cement selection
According to the curing mode, resin cements may be light-curing, dual-
curing or self-curing materials. Additionally, resin cements may be
categorized into the following three groups, based on the adhesive system
they use, i.e. – their adhesive approach.
1. Cements with etch-and-rinse adhesives
2. Cements with self-etching adhesives
3. Self-adhesive cements.
Resin cements with etch-and-rinse adhesives have been successfully
used with fiber posts for the longest period of time, and the vast majority of
clinical studies investigated this type of cements (Ferrari et al. 2000a; Ferrari
et al. 2000b; Malferrari et al. 2003; Mannocci et al. 2005; Monticelli et al.
2003; Grandini et al. 2005c; Naumann et al. 2005a; Naumann et al. 2005b;
Cagidiaco et al. 2007; Ferrari et al. 2007a; Ferrari et al. 2007b). Application
steps of etch-and-rinse adhesives in root dentin do not differ from coronal
dentin. However, etch and rinse adhesives are generally considered to be
technique sensitive (Van Meerbeek et al. 2003). The main reason for widely
discussed technique sensitivity of etch-and-rinse systems is the questionable
degree of surface wetness needed after rinsing the acid. While enamel should
preferably be dry to allow penetration of adhesive monomers, proper treating
of dentin is more complex. The etching and rinsing step leaves dentin surface
demineralized to a depth of 3-5μm (Perdigao et al. 1996). More importantly,
collagen fibers are exposed and left without inorganic support of
hydroxyapatite. In order to achieve penetration of resin monomers into such a
structure and assure interlocking, collapse of collagen fibers needs to be
prevented. It has been described that overdrying of dentin surface induces
collapse of collagen fibers which form a coagulate, thereby impeding proper
resin penetration (Pashley and Carvalho 1997). Depending on the kind of
13
solvent of the primer (or primer/adhesive in two-step systems), two different
clinical approaches have been described: wet and dry bonding (Gwinnett
1992; Kanca 1992). Regardless of the bonding technique used, the possibility
for discrepancy between depth of dentin demineralization and monomer
infiltration was recognized as a main drawback of etch-and-rinse adhesives
(Van Meerbeek et al. 1992; Sano et al. 1994; Wang and Spencer 2003).
Considering that in fiber post cementation these adhesives have to be applied
to the surface that cannot be properly visualized, it would be reasonable to
assume that they are even more technique sensitive when used in the root
canal. For this reason, it is often recommended to adapt every step to the
specific conditions of the post space. Phosphoric acid should be applied and
rinsed-off through a needle or a long tip, in order to reach the apical third of
the post space. Drying should be performed using paper points in order to
avoid desiccation of the dentin surface, while for adhesive application,
microbrushes should be used (Ferrari et al. 2002).
Cements used with self-etching adhesives are simpler and more user
friendly. Since rinsing phase is excluded, so is the need for establishing the
debatable optimal level of moisture on dentin surface, which significantly
reduces technique sensitivity. These systems are user-friendly due to reduced
number of application steps and reduced application time. Another
characteristic of self-etching systems is simultaneous demineralization and
infiltration of resin monomers as well as incorporation of smear layer into
hybrid layer.
The newest group of resin cements consists of self-adhesive cements,
which are by far the easiest to use and are becoming very popular. Some
products have application tips exclusively made for easy and efficient fiber
post cementation. These materials are still new and for this reason they were
given particular attention in a literature review that is presented in Chapter 3
14
of this thesis. The second study of Chapter 3 assessed fiber post adhesion
with resin cements from each of the above-mentioned three categories. In
order to determine the retentive strength of fiber posts, microtensile
(Bouillaguet et al. 2003; Mallmann et al. 2005; Monticelli et al. 2006) and
push-out (Kurtz et al. 2003; Bell et al. 2005; Goracci et al. 2005b) tests may
be used. In the study presented in Chapter 3, the thin-slice push-out strength
test was performed, since it was shown to be more reliable than the
microtensile technique for measuring the retentive strength of fiber posts to
root canal walls (Goracci et al. 2004).
Light transmission through fiber post
The vast majority of posts that are available to clinicians are claimed by the
manufacturers to transmit light. However, a study by Goracci et al
demonstrated that posts differ in the amount of transmitted light and that
some of the posts that are declared to transmit light do not transmit any light
at all (Goracci et al. 2008). Fiber posts were therefore divided into three
categories based on their light transmitting ability (Ferrari 2008):
1. Posts that permit light to pass in a consistent entity
2. Posts that permit light to pass only partially and do not transmit light
at the apical end of the post
3. Posts that do not permit light to irradiate at all.
It is advisable not to use light curing resin cements and adhesives
because of the post space depth that cannot be entirely reached by light. For
this reason, self curing and dual curing resin cements are strongly
recommended (Ferrari 2008). It appears that in clinical practice dual-curing
cements are most frequently used. Moreover, dual-curing resin cements were
used in several clinical studies on fiber posts (Ferrari et al. 2000b; Monticelli
et al. 2003; Grandini et al. 2005c; Naumann et al. 2005a; Naumann et al.
15
2005b; Cagidiaco et al. 2007; Ferrari et al. 2007b). These materials have the
advantage of adequately long working time, and still they can be cured on
demand when convenient for the clinician. They cure by light in areas that
light can reach, whereas in areas non reachable by light, chemical
polymerization takes place. However, it was reported that dual curing
cements reach far better mechanical properties in the presence of light, and it
is hence recommended to light cure them whenever possible (Caughman et
al. 2001; Kumbuloglu et al. 2004). The question remained whether this
property of dual curing cements in relation with light transmitting ability of
the post may in fact make a difference in fiber post cementation. It was not
known whether light transmission through the post may influence the quality
of post/cement/dentin interfaces. In an attempt to give an answer to these
questions, a study presented in Chapter 4 was performed.
16
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Saupe WA, Gluskin AH, Radke RA, Jr. (1996). A comparative study
of fracture resistance between morphologic dowel and cores and a resin-
reinforced dowel system in the intraradicular restoration of structurally
compromised roots. Quintessence Int 27(7): 483-91.
Schwartz RS, Robbins JW (2004). Post placement and restoration of
endodontically treated teeth: a literature review. J Endod 30(5): 289-301.
Signore A, Benedicenti S, Kaitsas V, Barone M, Angiero F, Ravera G
(2009). Long-term survival of endodontically treated, maxillary anterior teeth
restored with either tapered or parallel-sided glass-fiber posts and full-
ceramic crown coverage. J Dent 37(2): 115-21.
Stankiewicz NR, Wilson PR (2002). The ferrule effect: a literature
review. Int Endod J 35(7): 575-81.
22
Tan PL, Aquilino SA, Gratton DG, Stanford CM, Tan SC, Johnson
WT, Dawson D (2005). In vitro fracture resistance of endodontically treated
central incisors with varying ferrule heights and configurations. J Prosthet
Dent 93(4): 331-6.
Tay FR, Pashley DH (2007). Monoblocks in root canals: a
hypothetical or a tangible goal. J Endod 33(4): 391-8.
Trope M, Maltz DO, Tronstad L (1985). Resistance to fracture of
restored endodontically treated teeth. Endod Dent Traumatol 1(3): 108-11.
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(1992). Morphological aspects of the resin-dentin interdiffusion zone with
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�
23
Chapter 2: Treatments of fiber post surface
2.1. The effect of sandblasting on adhesion of a dual-cured resin
composite to methacrylic fiber posts: microtensile bond strength and
SEM evaluation
Ivana Radovic, Francesca Monticelli, Cecilia Goracci, Àlvaro Hafiz Cury,
Ivanovic Coniglio, Zoran R. Vulicevic, Franklin Garcia-Godoy, Marco
Ferrari. Journal of Dentistry 2007; 35(6): 496-502.
Introduction
Reconstructing endodontically treated teeth with prefabricated fiber post and
core systems has been widely accepted as a treatment option offering both
esthetics and function (Schwartz and Robbins 2004; Schwartz and Fransman
2005). The advantages of fiber post and core restorations have been
demonstrated in in vitro studies (Martinez-Insua et al. 1998; Sirimai et al.
1999; Cormier et al. 2001; Akkayan and Gulmez 2002; Newman et al. 2003;
Fokkinga et al. 2004; Hayashi et al. 2006). These systems can reduce the
incidence of non-retrievable root fractures when compared to prefabricated
metallic posts or conventional cast posts (Martinez-Insua et al. 1998; Sirimai
et al. 1999; Cormier et al. 2001; Akkayan and Gulmez 2002; Newman et al.
2003; Fokkinga et al. 2004; Hayashi et al. 2006). Retrospective (Fredriksson
et al. 1998; Ferrari et al. 2000; Ferrari et al. 2000) and prospective (Glazer
2000; Mannocci et al. 2002; Malferrari et al. 2003; Monticelli et al. 2003;
Naumann et al. 2005a; Naumann et al. 2005b) clinical studies have shown
overall satisfactory performance of endodontically treated teeth restored with
fiber post and core systems.
24
An important characteristic of fiber posts is a modulus of elasticity
similar to dentin, resin cements and resin core materials (Asmussen et al.
1999). This feature is most beneficial in the presence of a homogeneous post-
composite-dentin structure that would allow optimal stress distribution (De
Santis et al. 2000). Therefore, the importance of optimal coupling between
fiber post system components has been recognized and investigated. A
number of studies focused particularly on the possibility to improve adhesion
at the fiber post-composite interface through various treatments of post
surface (Sahafi et al. 2003; Sahafi et al. 2004a; Asmussen et al. 2005;
Goracci et al. 2005; Balbosh and Kern 2006; Bitter et al. 2006; Monticelli et
al. 2006a; Monticelli et al. 2006b; Monticelli et al. 2006c).
An increase in bond strength to flowable composites was observed
when fiber posts were silanized (Goracci et al. 2005), treated with a
combination of hydrogen peroxide etching and silanization (Monticelli et al.
2006c) as well as when chemical pretreatment with potassium permanganate
followed by silanization was employed (Monticelli et al. 2006b).
Furthermore, application of the silane/adhesive coupling was shown to
improve bond strength to hybrid composite (Monticelli et al. 2006a).
Adhesion of dual-cure resin composite to epoxy resin-based fiber posts was
improved when the post surface was treated with a dual cured bonding agent
or was silanized (Aksornmuang et al. 2004).
The possibility of improving the adhesion between fiber posts and
resin cements has been investigated to a somewhat lesser extent.
Sandblasting followed by silane coating, sandblasting alone and
tribochemical treatment (CoJet) significantly increased shear bond strength of
resin cements to methacrylate based glass fiber posts (Sahafi et al. 2003).
CoJet treatment significantly increased the resistance to cyclic loading of
teeth restored with adhesively luted glass fiber posts, which was assumed to
25
derive from an effective bonding of resin cement to the posts with a
reinforcing effect on the teeth (Sahafi et al. 2005). Sandblasting of the
surface of the glass-fiber epoxy resin posts significantly improved the
retention of posts adhesively luted with dual cured resin cement (Balbosh and
Kern 2006).
Sandblasting is routinely applied in general industry to provide
surface roughening making materials more bondable. It is commonly
employed in ceramic (Chung and Hwang 1997) and composite repair
procedures (Swift et al. 1992; Pontes et al. 2005; Papacchini et al. 2008),
indirect composite bonding (Swift et al. 1992), for pretreatment of metal
surface in metal-ceramic restorations (Winkler and Wongthai 1986), or as a
part of a tribochemical silica-coating process (Kern and Thompson 1993).
Nevertheless, the information on the effect of sandblasting alone or
combined with additional “chair-side” treatments on bond strength to fiber
posts is lacking. Therefore, the aim of this investigation was to evaluate the
influence of sandblasting pretreatment and different “chair-side” treatments
of methacrylate based fiber posts on the microtensile bond strength with a
dual-cured resin composite. The null hypothesis tested was that various
combinations of surface pre-treatment and “chair-side” treatment did not
influence the adhesion of methacrylate based fiber posts to dual-cured resin
composite.
Materials and Methods
Thirty two translucent methacrylate-based glass fiber posts (GC Corporation,
Tokyo, Japan) with a diameter of 1.6 mm were used in the study. Posts were
divided into two groups, according to the surface pretreatment performed.
Group 1: Sandblasting with 110μm aluminum oxide particles (Rocatec-Pre,
26
3M ESPE, St. Paul, MN, USA) for 5 seconds at 2.8 bar (0.28 MPa) from a
distance of 1 cm. In Group 2 no pretreatment was performed. Each group was
further divided into three subgroups (n=5), according to the additional “chair-
side” treatment performed. Subgroup 1: silane application (Monobond S,
Ivoclar Vivadent, Schaan, Liechtenstein); Subgroup 2: adhesive application
(Unifil Core self-etching bond, GC Corporation); Subgroup 3: no additional
“chair-side” treatment. The materials were used according to the
manufacturers’ instructions. The chemical composition, batch numbers and
the application modes are reported in Table 1.
Composite build-up and microtensile bond strength test procedures
A dual-cured resin composite (Unifil Core, GC Corporation) was applied on
the posts to produce cylindrical specimens with the post in the center, using a
transparent plastic matrix. The procedure previously described by Goracci et
al. for core build-up materials was followed (Goracci et al. 2005). All
specimens were prepared by one investigator to ensure standardization. Each
post was positioned upright on a glass slab, and secured with a drop of sticky
wax. A cylindrical plastic matrix was placed around the post and adjusted so
that the post would be exactly in the middle. The matrix was 10 mm in
diameter. In height, the matrix was extended only to the cylindrical portion of
the post (about 10 mm), since for an appropriate cutting of the microtensile
specimens, it is desirable that the post diameter is constant throughout the
post length. The two components of resin composite were mixed, applied on
the post filling the matrix completely, and light cured for 40 s with a halogen
curing light (600 mW/cm2 output; VIP; Bisco, Schaumburg, IL, USA)
directly from the open upper side of the matrix and through the post.
27
Table 1: Composition, batch numbers and the application mode of the
materials used in the study
Material Composition1 Application mode Rocatec-Pre Aluminum oxide
(particle size: 110 μm)
Sandblasting from a distance of 1 cm at 2.8 Bar (0.28 MPa) for 5 sec.2
Monobond S (Ivoclar Vivadent) Batch no. F68158
1% 3-methacryloxypropyltrimethoxysilane (3-MPS), ethanol/water-based solvent
Apply to the post surface. Air dry after 60 seconds.
Unifil Core self-etching bond (GC Corporation) Batch no. 0511251
Liquid A: Ethanol, water, 4-MET, dimethacrylate, silica, catalyst Liquid B: Ethanol, catalyst
Mix liquid A and Liquid B; (1:1) apply mixture to the post surface for 1-2 seconds; gently air dry; light cure
Unifil Core Resin Cement/Core material (GC Corporation) Batch no. 0511251
Pastes A and B: Urethane dimethacrylate, dimethacrylate, photo/chemical initiator, fluoro-amino silicate glass
Mix components; seat the post immediately; light cure.
GC fiber post (GC Corporation) Batch no. 21700BZZ00408000
Glass fibers (77% vol), methacrylate resin matrix (23% vol)
-
1 Information from the manufacturers. 2 Manufacturer’s recommended procedure is: sandblast from the distance of 1cm2 at 2.8 Bar for 15 seconds for the area of approximately 1cm2. Considering the size of fiber posts, the sandblasting time was reduced to 5 seconds.
28
Additional 40 s irradiations were performed from each side of the cylinder
prior to the removal of the matrix to ensure optimal polymerization of the
composite material.
Cylinders were mounted in a cutting machine (Isomet 1000, Buehler,
Lake Bluff, IL, USA) and sectioned under water cooling to obtain a slab of
uniform thickness, with the post in the center and composite on each side.
From each slab, 6-8 sticks of 1-mm in thickness were obtained, resulting in
the multiple specimens (32 on average per subgroup) that were available for
microtensile bond strength testing. Beams were glued (Super Attak Gel,
Henkel Loctite Adesivi S.r.l., Milano, Italy) to the two free sliding
components of a jig, which was mounted on a universal testing machine
(Triax, Controls S.P.A., Milano, Italy) and loaded in tension at a crosshead
speed of 0.5 mm/min until failure occurred at either side of the post-
composite interface. The dimensions of the interface on each beam were
measured with a digital caliper to the nearest 0.01 mm. No pretesting failures
occurred during cutting and testing procedures. Schematic drawing of
specimen preparation for microtensile testing is shown in Figure 1.
Failure modes were evaluated with a stereomicroscope (Nikon
SMZ645, Tokyo, Japan) at 40x magnification and recorded as adhesive (at
the post/composite interface), cohesive (within the post or the composite) or
mixed (a combination of the two modes of failure in the same interface).
Bond strength was expressed in MegaPascals (MPa), dividing the load at
failure in Newtons by the bonding surface area. As the bonded interface was
curved, its area was calculated using a mathematical formula previously
applied by Bouillaguet et al (Bouillaguet et al. 2003).
29
Figure 1: Schematic drawing of specimen preparation for microtensile bond
strength testing. C: composite; P: post.
SEM evaluation
One post was randomly selected from each of the two main groups for SEM
examination of the surface morphology. The posts were ultrasonicated in
96% alcohol for 2 min and air dried. Following core build-up procedure, one
post-composite cylinder from each subgroup was randomly chosen for the
SEM evaluation of the bonded interface. Samples were cut into 1.5 mm thick
cross-sections (Isomet 1000; Buehler). Sections were polished with wet
abrasive SiC papers, cleaned with orthophosphoric acid for 15 s, rinsed with
water, ultrasonicated in 96% alcohol for 2 min and air dried. Each specimen
was mounted on a metallic stub, sputtered with gold-palladium (Polaron
Range SC7620; Quorum Technology, Newhaven, UK), and observed under
an SEM (JSM 6060 LV, JEOL, Tokyo, Japan) at different magnifications.
30
Statistical analysis of the microtensile bond strength data
A preliminary linear regression analysis showed that the post–composite
cylinder did not have a significant influence on the measured bond strength;
therefore, the sticks were considered as independent within each group. After
analyzing the bond strength data for the normality of data distribution
(Kolmogorov–Smirnov test) and homogeneity of variances (Levene’s test), a
two-way ANOVA was applied with bond strength as the dependent variable,
and types of surface pretreatment and “chair-side” treatment as factors. The
Tukey test was used for post hoc comparisons. In all the tests, the level of
significance was set at p<0.05 and calculations were handled by the SPSS
13.0 software (SPSS Inc.; Chicago, IL, USA).
Results
Interfacial Bond Strength
Results of microtensile bond strength testing are summarized in Table 2 and
Figure 2. Statistical analysis revealed that post surface pretreatment was not a
significant factor (p=0.08), while ‘‘chair-side’’ treatment had a significant
influence on bond strength (p<0.001). When the results were pooled for each
‘‘chair-side’’ treatment regardless of the pretreatment, post hoc comparisons
(Tukey test) revealed that no ‘‘chairside’’ treatment and silanization resulted
in comparable bond strengths while the values were significantly lower when
the adhesive was applied. The interaction of the two factors was also
significant (p<0.001). This lead to post hoc comparisons (Tukey test) in
which all six groups were compared to assess which group means differed
from which others. The Tukey test revealed that sandblasting significantly
improved bond strength when no ‘‘chair-side’’ treatment was performed
(Table 2). The values in this group were comparable to experimental groups
31
‘‘sandblasting/Monobond S’’ and ‘‘no pretreatment/Monobond S’’. Adhesive
application resulted in significantly lower bond strength on sandblasted posts,
while on conventional posts results were comparable with no ‘‘chair-side’’
treatment. Application of silane had no influence on bond strength, regardless
of the pretreatment. In group ‘‘sandblasting/Monobond S’’ and
‘‘sandblasting/no treatment’’ cohesive failures within the fiber post occurred
in 47 and 35% of tested beams, respectively. In the other groups the most
frequent type of failure was adhesive (Figure 3).
Table 2: Post-composite microtensile bond strength [MPa]. Numbers are
means. Values in brackets are standard deviations. Different superscript
letters indicate statistically significant differences.
Pretreatment
Treatment Sandblasting None
Monobond S 19.76 [6.16]AB 21.67 [7.13]AB
Unifil Core self-etching bond 14.29 [6.02]C 14.12 [4.90]C
None 23.97 [6.82]A 17.67 [5.31]BC
32
Figure 2: Post-composite microtensile bond strength
SANDBLASTINGNO PRETREATMENT
� � �
Monobond SUnifil Core self-etching bond
No treatment
�
�
�
�
10
20
30
40
[MPa
]
Figure 3: Failure distribution. M: mixed failure. CC: cohesive failure within
the cement. CP: cohesive failure within the post. A: adhesive failure.
33
SEM evaluation
Sandblasting created a rough surface along the entire post length (Figure 4A),
providing additional spaces for micromechanical retention compared to the
surface of a conventional post (Figure 4B). Cross-sections of the post-
composite interfaces exhibited a good adaptation of the resin composite to
the post surface in groups: “sandblasting/Monobond S”, “sandblasting/no
treatment”, “no pretreatment/Monobond S” and “no pretreatment/no
treatment” (not shown). No defects and no discontinuities occurred along the
interface, and no significant differences in the morphology of the interface
between these groups were noticed. In groups where adhesive was applied,
gaps between the post surface and the adhesive layer were frequently
observed, both on sandblasted and conventional posts (not shown), without
significant differences in gap occurrence and morphological appearance.
34
Figure 4. Representative SEM micrographs of a post-surface. After
sandblasting (A) the surface appeared more retentive compared to the
conventional post surface (B).
A
B
35
Discussion
Unifil Core belongs to the group of materials that are formulated to be used
both for cementation and core-build-up procedures. However, the
experimental set-up employed in this investigation has limitations that render
it more appropriate for simulating a core-build-up procedure than a luting
procedure. The amount of material that was placed around the posts is
considerably thicker than the cement layer between the fiber post and root
canal. In the clinical situation, a much higher C-factor is present, as well as
an unfavorable interaction between C-factor and shrinkage stress that could
interfere with bond strength values (Tay et al. 2005). However, microtensile
tests allow bond strength measurements between resin cements or core
materials and surface of fiber posts. Assessing fiber post-resin cement bond
strength with conventional shear bond strength tests required the post surface
to be removed (Sahafi et al. 2003), while tensile bond strength tests have
been conducted with discs of post materials (O'Keefe et al. 2000; Sahmali et
al. 2004). Therefore, microtensile bond strength values measured after
bonding to the original post surface may be advantageous and more clinically
relevant.
Significant differences in bond strength were found between
experimental groups, which led to the rejection of the null hypothesis. The
highest bond strength was recorded on sandblasted posts with no additional
“chair-side” treatment. Results in this group were significantly better than the
results on conventional posts with no additional treatment. SEM evaluation
supported bond strength data (Figure 4A), revealing a more retentive surface
created by sandblasting. This finding is in accordance with others
demonstrating the beneficial influence of sandblasting on retention of epoxy
resin based fiber posts (Balbosh and Kern 2006). Significantly higher bond
36
strengths of resin cements to sandblasted posts were also observed on
methacrylate (Sahafi et al. 2003) and epoxy resin-based fiber posts (Wang et
al, unpublished data, 2006).
Application of silane did not result in increase in bond strength,
regardless of the pretreatment. This finding is in contrast with previous
studies that reported beneficial influence of silanization on bond strength to
conventional (Goracci et al. 2005) and sandblasted fiber posts (Sahafi et al.
2003). The mechanism of silane action relies on formation of bonds between
its functional alkoxy groups and OH-covered inorganic substrates. Since the
resin matrix of fiber posts contains highly cross-linked monomers, only the
exposed fibers on the post surface could provide sites for chemical bonding
with the silane molecules. As the contribution of such a chemical interaction
to fiber post-composite bond strength is considered to be fairly low, it is
assumed that the increase in surface wettability induced by silane application
plays a more important role (Goracci et al. 2005). However, it was shown
that surface energy characteristics of adherend and adhesive determine fiber
post-composite bond strength in the minor part, while the other factors
remained to be identified (Asmussen et al. 2005). Bond strength of Unifil
Core to epoxy resin fiber posts silanized with Monobond S (Sadek et al.
2007) was noticeably lower than in the present investigation. Since GC fiber
post is methacrylate based, it can be speculated that the dual-cured resin
composite bonded to the organic matrix of fiber posts, consequently
influencing bond strength to a greater extent than the potential surface
wetting capacity of the silane applied. Nevertheless, bond strength to
conventional silanized posts (“no pretreatment/Monobond S”) was
comparable to bond strength to sandblasted posts (“sandblasting/no
treatment”) (Table 2).
37
Monobond S is a single component pre-hydrolyzed silane. On the
other side, two-component systems have been introduced for “on-demand”
hydrolysis. In these systems the silane is rapidly hydrolyzed when mixed
with the acidic phosphate monomers like 10-MDP (10-methacryloloxydecyl
dihydrogenphosphate), which are present in the water-containing dentin
adhesives. It would be of interest to investigate whether the beneficial effect
of a two-component system on epoxy resin-based fiber posts (Aksornmuang
et al. 2004; Monticelli et al. 2006a) could be observed using fiber posts that
contain methacrylate matrix.
Coating the posts with the proprietary self etching adhesive (Unifil
Core self-etching bond) resulted in the lowest bond strengths, regardless of
the pretreatment. Moreover, gaps were frequently observed between the post
and the adhesive layer. No discontinuities were seen between the adhesive
layer and the cement. In contrast to these findings, the application of a dual
cured bonding agent significantly improved adhesion to epoxy resin based
fiber posts (Aksornmuang et al. 2004). The authors speculate that the water
content and acidity of the self-etching adhesive used in this study may have
influenced bonding to fiber post surface. A possible mechanism involved
could be the phase separation of adhesive monomers from water upon
evaporation of ethanol solvent, that was demonstrated to occur in HEMA-
free (2-hydroxyethyl methacrylate) one-step self-etching adhesives (Van
Landuyt et al. 2005). Remnants of water may have affected the
polymerization of the adhesive, decreasing bond strength and influencing gap
formation at the adhesive-post interface.
In general, higher bond strengths resulted in a superior percentage of
cohesive failures (Figure 3), correlating with previous investigations of other
authors (O'Keefe et al. 2000; Sahmali et al. 2004). The vast majority of
cohesive failures occurred within the fiber post, which may be the result of an
38
unfavorable coupling between glass fibers and methacrylate matrix of the
fiber post.
Although sandblasting may give an increase in microtensile strength
to methacrylate-based glass fiber posts, its effects should be further
investigated. Concern was raised regarding the possible volume loss induced
by sandblasting or tribochemical coating procedures (Sahafi et al. 2004b).
Therefore, further research is necessary in order to agree on the optimal
particle size, distance, pressure and time of application. Additional
application of a self-etching adhesive to methacrylate-based fiber posts
should be avoided, since no increase in bond strength could be observed.
Moreover, long term durability of fiber post-composite bonds following
various treatments of post surface under clinical and laboratory conditions
remains to be determined.
Conclusion
Sandblasting may give an increase in microtensile strength to methacrylate-
based glass fiber posts, eliminating the need to apply additional ‘‘chair-side’’
treatments. Reducing the number of clinical steps could contribute to
simplify the clinical procedures.
39
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Shear bond strength of direct composite repairs in indirect composite
systems. Gen Dent 53(5): 343-7.
Sadek FT, Monticelli F, Goracci C, Tay FR, Cardoso PE, Ferrari M
(2007). Bond strength performance of different resin composites used as core
materials around fiber posts. Dent Mater 23(1): 95-9.
Sahafi A, Peutzfeld A, Asmussen E, Gotfredsen K (2004a). Effect of
surface treatment of prefabricated posts on bonding of resin cement. Oper
Dent 29(1): 60-8.
Sahafi A, Peutzfeldt A, Asmussen E, Gotfredsen K (2003). Bond
strength of resin cement to dentin and to surface-treated posts of titanium
alloy, glass fiber, and zirconia. J Adhes Dent 5(2): 153-62.
Sahafi A, Peutzfeldt A, Asmussen E, Gotfredsen K (2004b).
Retention and failure morphology of prefabricated posts. Int J Prosthodont
17(3): 307-12.
43
Sahafi A, Peutzfeldt A, Ravnholt G, Asmussen E, Gotfredsen K
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Investig 9(2): 84-90.
Sahmali S, Demirel F, Saygili G (2004). Comparison of in vitro
tensile bond strengths of luting cements to metallic and tooth-colored posts.
Int J Periodontics Restorative Dent 24(3): 256-63.
Schwartz RS, Fransman R (2005). Adhesive dentistry and
endodontics: materials, clinical strategies and procedures for restoration of
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Schwartz RS, Robbins JW (2004). Post placement and restoration of
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fracture resistance and the incidence of vertical root fracture of pulpless teeth
restored with six post-and-core systems. J Prosthet Dent 81(3): 262-9.
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composite surfaces for indirect bonding. Dent Mater 8(3): 193-6.
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Geometric factors affecting dentin bonding in root canals: a theoretical
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Van Landuyt KL, De Munck J, Snauwaert J, Coutinho E, Poitevin A,
Yoshida Y, Inoue S, Peumans M, Suzuki K, Lambrechts P, Van Meerbeek B
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44
2.2. Accelerated aging of adhesive-mediated fiber post-resin composite
bonds: a modeling approach
Ivana Radovic, Francesca Monticelli, Federica Papacchini, Elisa Magni,
Àlvaro Hafiz Cury, Zoran R. Vulicevic, Marco Ferrari. Journal of Dentistry
2007; 35(8): 683-689.
Introduction
The importance of coronal seal for the long-term clinical success of
endodontically treated teeth is well established (Saunders and Saunders 1994;
Begotka and Hartwell 1996; Tronstad et al. 2000). If fiber reinforced
composite (FRC) post-retained adhesive restorations are chosen, the resin
composite used for the build-up as well as the luting cement play a
significant role in the establishment and maintenance of a durable coronal
seal (Bachicha et al. 1998; Mannocci et al. 2001; Rogic-Barbic et al. 2006).
Although resin cements resulted in a significantly lower microleakage extent
than conventional zinc phosphate (Bachicha et al. 1998; Mannocci et al.
2001; Rogic-Barbic et al. 2006) or glass ionomer cement (Bachicha et al.
1998), it has been reported that none of the luting materials is able to
completely prevent leakage. Furthermore, it has been reported that the
combination of some simplified adhesives and resin cements for luting to
radicular dentin may result in a fluid movement phenomenon across the
adhesive layer in vivo, with the formers behaving as permeable membranes
even after polymerization (Chersoni et al. 2005). Thus, the importance of
investigating and improving the coupling between FRC posts and the
materials used for luting has been recognized.
In particular, the link established between the FRC post and the resin
cement or core material may contribute to the coronal seal and homogeneity
45
of post-retained adhesive restorations, as well as to optimal stress distribution
during clinical function (De Santis et al. 2000). Since failure may eventually
occur at this interface (Pirani et al. 2005; Perdigao et al. 2006), numerous
post surface treatments have been recently investigated, aiming to enhance
the adhesion between prefabricated FRC posts and resin composites (Sahafi
et al. 2003; Aksornmuang et al. 2004; Sahafi et al. 2004; Goracci et al. 2005;
Aksornmuang et al. 2006; Balbosh and Kern 2006; Bitter et al. 2006;
Monticelli et al. 2006a; Monticelli et al. 2006b; Radovic et al. 2007). The
adhesion of resin cements to FRC posts with a semi-interpenetrating polymer
network (IPN) polymer matrix has been recently investigated. It was reported
that these posts bonded better to resin cements in comparison with
prefabricated FRC posts with a cross-linked polymer matrix (Le Bell et al.
2004; Mannocci et al. 2005).
The application of a dual-cured adhesive on FRC post surface
represents a simple and effective chair-side treatment that can improve the
adhesion of core materials to epoxy resin-based quartz fiber posts
(Aksornmuang et al. 2004; Aksornmuang et al. 2006). Nevertheless, the
information about the stability of this interface in the presence of an aging
medium is missing in the literature. The hydrolytic stability of fiber post-core
bonds has been assessed in only one study, revealing that silane-mediated
bonds were susceptible to hydrolytic degradation in vitro when a highly
hydrophilic silane was used, with a subsequent decline in post-core bond
strength (Monticelli et al. 2006). In the light of these findings, it may be of
interest to evaluate the stability of fiber post-composite bonds mediated by a
resinous coupling agent like an adhesive layer rather than methacrylate-based
silanes. Sandblasting followed by silane application is a beneficial procedure
for enhancing the bond strength of resin cements to methacrylate-based glass
FRC posts (Sahafi et al. 2003; Magni et al. 2007). However, it should be
46
evaluated whether bond strength to epoxy resin-based FRC posts can be
further enhanced if adhesive application is preceded by sandblasting.
The objectives of this study were: 1. to evaluate the influence of water
storage on adhesive-mediated FRC post-resin cement and FRC post-flowable
composite bonds using a model of accelerated aging, and 2. to investigate
whether previous sandblasting influences post-composite bond strength. The
following null hypotheses were tested:
(1) Pretreatment of FRC post surface has no influence on bond strength to
resin cement and flowable composite;
(2) there is no difference between FRC post-cement and FRC post-flowable
composite bond strength;
(3) the accelerated water aging procedure does not influence bond strength of
resin cement and flowable composite to epoxy resin-based FRC posts,
regardless of post surface treatment.
Materials and Methods
Forty translucent epoxy resin-based quartz FRC posts (DT Light Post #3 –
RTD, St Egrève, France) with a diameter of 2.14 mm were used in the study.
Posts were randomly divided into two groups of 20 each, according to the
surface treatment to be performed. In group I posts were treated with an etch-
and-rinse adhesive XPBond (Dentsply Caulk, Milford, DE, USA). In group II
posts were sandblasted (aluminum oxide, particle size 110 μm; Rocatec-Pre,
3M ESPE, St. Paul, MN, USA) for 5 seconds at 0.28 MPa from a distance of
1cm, and then treated with XPBond adhesive. Posts were manually rotated
during the sandblasting procedure. On all the posts the adhesive was used in
the self-curing mode. Each experimental group was then divided into two
subgroups (n=10), according to the resin cement/core material to be applied
47
on the posts. FRC posts were coupled with a dual-cured resin cement
(Calibra, Dentsply Caulk; Subgroup 1) and a flowable composite (X-Flow,
Dentsply Caulk; Subgroup 2). The materials were used according to the
manufacturer’s instructions. The chemical composition, batch numbers and
the application modes are reported in Table 1.
Coupling of resin cement/flowable composite and microtensile bond strength
test procedures
Schematic flow chart of specimen preparation for microtensile testing is
shown in Figure 1. Resin cement and flowable composite were applied on the
posts to produce cylindrical specimens with the post in the center, using a
transparent plastic matrix. The procedure previously described by Goracci et
al. for core build-up materials was followed (Goracci et al. 2005). All
specimens were prepared and cut by the same investigator to ensure
standardization. Each post was positioned up-right on a glass slab, and
secured with a drop of sticky wax. A cylindrical disposable plastic matrix
was placed around the post and adjusted so that the post would be exactly in
the middle. The matrix was 10 mm in diameter.
48
Table 1: Composition, batch numbers and the application mode of the
materials used in the study
Material Composition Application mode
Rocatec-Pre (3M ESPE)
Aluminum oxide (particle size: 110 μm)
Sandblasting from a distanceof 1 cm at 0.28 MPa for 5 seconds.3
XPBond adhesive (Dentsply Caulk) Batch no. 0503004020
carboxylic acid modified dimethacrylate (TCB resin), phosphoric acid modified acrylate resin (PENTA), urethane dimethacrylate (UDMA), triethyleneglycol dimethacrylate (TEGDMA), 2-hydroxyethylmethacrylate (HEMA), Butylated benzenediol (stabilizer), ethyl-4-dimethylaminobenzoate, camphorquinone, functionalised amorphous silica, t-butanol
Mix XPBond adhesive with Self-Cure Activator (1:1); apply mixture to the post surface for 1-2 s; gently air dry.
Self-cure activator (Dentsply Caulk) Batch no. 040901
Aromatic Sodium Sulfinate, (Self cure initiator), Acetone, Ethanol
Calibra Esthetic Resin Cement (Dentsply Caulk) Batch no. 050412 Batch no. 0506142
Base: Dimethacrylate Resins; Camphorquinone (CQ) Photoinitiator; Stabilizers; Glass Fillers; Fumed silica; Titanium Dioxide; Pigments Catalyst: Dimethacrylate Resins; Catalyst; Stabilizers; Glass Fillers; Fumed Silica
Mix cement components; seat the post immediately; light cure.
X-Flow flowable composite (Dentsply Caulk) Batch no. 0412000740
Strontium alumino sodium fluoro phosphor silicate glass, Di- and multifunctional acrylate and methacrylate resins, Diethylene glycol dimethacrylate (DGDMA), Highly dispersed silicon dioxide, UV stabiliser, Ethyl-4-dimethylaminobenzoate, Camphor quinone, Butylated hydroxy toluene (BHT), Iron pigments, Titanium dioxide
Dispense directly into the matrix in 2 mm layers; light cure.
DT Light Post (RTD St Egreve France) Batch no. 00447200506
Epoxy resin (40%); quartz fibers (60%) -
3 Manufacturer’s recommended procedure is: sandblast from the distance of 1cm at 0.28 MPa for 15 seconds for the area of approximately 1cm2. Considering the size of fiber posts, the sandblasting time was reduced to 5 seconds.
49
Figure 1: Schematic drawing of specimen preparation for microtensile bond
strength testing. C: cement/composite; P: fiber post.
In height, the matrix was extended only to the cylindrical portion of the post
(about 10 mm), since for an appropriate cutting of the microtensile
specimens, it is desirable that the post diameter is constant throughout the
post length. The resin cement was mixed, applied on the post filling the
matrix completely, and light cured for 40 s with a halogen curing light (600
mW/cm2 output; VIP; Bisco, Schaumburg, IL, USA) directly from the open
upper side of the matrix and through the post. Additional 40 s irradiations
were performed from each side of the cylinder prior to the removal of the
matrix to ensure optimal polymerization of the material. The flowable
composite was applied to the post in 1–2mm thick increments. Each
increment was carefully adapted to the post surface and light-cured
separately.
50
The bond strength at the interface between post and
cement/composite was measured with the microtensile non-trimming
technique (Shono et al. 1999). The sectioning of the specimens began on
completion of the cementation/core build-up procedure. In each subgroup, 5
cylinders were used to obtain microtensile sticks that were to be tested
immediately (Subgroups 1A and 2A, Figure 1). Sticks obtained from the
remaining 5 cylinders (Subgroups 1B and 2B, Figure 1) were stored in
deionized water at 37ºC for 1 month prior to microtensile bond strength
testing. Cylinders were mounted in a cutting machine (Isomet 1000, Buehler,
Lake Bluff, IL, USA) and sectioned under water cooling to obtain a slab of
uniform thickness, with the post in the center and cement/flowable composite
on each side. Each slab was further sectioned into sticks of 1 mm in
thickness, resulting in the mean of 30 specimens per final experimental
condition (Group/Subgroup/time of bond strength test: A or B). The cylinder
of origin was noted for every stick. The number of prematurely failed sticks
during the cutting procedures was noted and is reported in Table 2. For each
of the prematurely failed sticks bond strength value was recorded as 0 MPa
and included in the statistical analysis. Sticks were glued (Super Attak Gel,
Henkel Loctite Adesivi S.r.l., Milano, Italy) to the two free sliding
components of a jig, which was mounted on a universal testing machine
(Triax, Controls S.P.A., Milano. Italy) and loaded in tension at a crosshead
speed of 0.5 mm/min until failure occurred at either side of the post-
composite interface. No sticks failed prematurely during the testing step.
Failure modes were evaluated with a stereomicroscope (Nikon
SMZ645, Nikon Co., Tokyo, Japan) at 40x magnification and recorded as
adhesive (at the post/cement or post/composite interface), cohesive (within
the post, cement or the composite) or mixed (a combination of the two modes
of failure in the same interface). Bond strength was expressed in
51
MegaPascals (MPa), dividing the load at failure in Newtons by the bonding
surface area. As the bonded interface was curved, its area was calculated
using a mathematical formula previously applied by Bouillaguet et al. for
similar purposes (Bouillaguet et al. 2003).
SEM evaluation
Two additional post/cement or post/flowable composite cylinders were
prepared per each subgroup in order to evaluate the adhesive interface prior
and after water aging. The cylinders were immediately cut into 1.5 mm thick
cross-sections. Half of the sections obtained was immediately processed for
SEM evaluation while the other half was evaluated after 1 month of water
storage at 37ºC. Sections were cleaned with 32% silica-free phosphoric acid
gel (Uni-Etch, Bisco, Schaumburg, IL, USA) for 15 seconds, rinsed with
water, rinsed in 96% alcohol solution for 1 minute and air-dried. Each section
was mounted on a metallic stub, sputter-coated with gold (Polaron Range
SC7620; Quorum Technology), and observed under a scanning electron
microscope (JSM 6060 LV, JEOL) at different magnifications.
Statistical analysis of the microtensile bond strength data
As a preliminary linear regression analysis showed that neither the post-
cement nor the post-flowable composite cylinder had a significant influence
on the measured bond strength, sticks were considered as independent within
each experimental group (i.e. final experimental condition -
Group/Subgroup/time of bond strength test: A or B). As the bond strength
data was not normally distributed (Kolmogorov–Smirnov test), Kruskal-
Wallis analysis of variance was applied, followed by Dunn’s multiple range
test for the post-hoc comparisons. In all the tests, the level of significance
52
was set at p<0.05 and calculations were handled by the SPSS 13.0 software
(SPSS Inc.; Chicago, IL, USA).
Results
Interfacial Bond Strength
Results of microtensile bond strength testing are reported in Table 2.
Sandblasting followed by adhesive coating significantly improved immediate
post-composite bond strength in comparison to adhesive alone, for each of
the two materials tested. After water aging, the two post surface treatments
attained comparable bond strengths, when comparing groups in which the
same material was used. Resin cement achieved higher bond strength to fiber
posts than flowable composite when the groups with the same post surface
treatment were compared, both immediately and after 1 month. Fiber post-
resin cement and fiber post-flowable composite bond strengths were
significantly lower after accelerated water aging. Failure distribution is
reported in Table 3. In general, higher bond strengths resulted in a superior
percentage of cohesive or mixed failures.
53
Table 2: Post-cement and post-flowable composite microtensile bond
strength (MPa) prior and after water storage and number of pretesting failures
(pf). Values are means. Numbers in brackets are standard deviations.
Different letters indicate statistically significant differences within the
column. Different numbers indicate statistically significant differences within
the row (Kruskal-Wallis analysis of variance followed by Dunn’s multiple
range test, p<0.05)
Storage
Treatment Material No storage 1 month water
XPBond
Calibra 21.32 (5.18) B1
pf: 0 of 29 15.59 (5.67) A2
pf: 0 of 39
X-Flow 9.77 (8.68) C1
pf: 9 of 25 3.93 (3.26) B2
pf: 7 of 36
Sandblasting + XPBond
Calibra
26.57 (7.61) A1 pf: 0 of 26
15.65 (6.48) A2 pf: 0 of 28
X-Flow
18.03 (6.31) B1 pf: 0 of 30
7.57 (3.53) B2 pf: 0 of 33
Table 3: Percentage of different types of testing failures. A: adhesive failure;
M: mixed failure; CP: cohesive failure in the fiber post; CC: cohesive failure
in cement/flowable composite.
Treatment Material Storage Type of testing failure (%) A M CP CC
XPBond
Calibra
No storage 76 0 21 3
1 month, water 85 5 10 0
X-Flow
No storage 100 0 0 0
1 month, water 100 0 0 0
Sandblasting + XPBond
Calibra
No storage 58 27 8 7
1 month, water 50 18 29 3
X-Flow
No storage 87 3 10 0
1 month, water 91 9 0 0
54
SEM evaluation
SEM evaluation of the immediately processed cross-sections revealed a good
adaptation of the resin cement (Figure 2A and 2C) and the flowable
composite (Figure 2E and 2G) to the post surface, irrespective of the
pretreatment. No defects and no discontinuities occurred along the interface,
and no significant differences in the morphology of the interface between
these groups were noticed. In cross-sections that were stored in water for 1
month, gaps between the post surface and resin cement (Figure 2B and 2D)
or flowable composite (Figure 2F and 2H) were frequently observed,
regardless of the pretreatment and without significant differences in gap
occurrence and morphological appearance.
Figure 2: SEM micrographs of the post-cement (A-D) and post-flowable
composite (E-H) interfaces prior (A, C, E, G) and after water aging (B, D, F,
H). Immediately examined interfaces revealed the absence of any defects or
discontinuities. No differences were noticed between the groups where post
surface was treated with XPBond adhesive (A, E) and the groups where
adhesive application was preceded with sandblasting (C, G). One-month
water storage resulted in the frequent occurrence of gaps at the interface, both
on posts treated with the adhesive (B, F) and the posts that were previously
sandblasted (D, H).
55
56
Discussion
A general agreement on how to statistically treat the prematurely failed
specimens during microtensile bond strength testing is presently lacking in
the literature. They may be excluded, considered as zero or greater than zero
values (Pashley et al. 1999). In the present study, it was decided to include
the prematurely failed sticks to the statistical analysis as “zero bonds”,
assuming that specimens that fail prior to testing are most likely the
expression of a relatively weaker bond (Pashley et al. 1999).
The three study variables (post surface treatment, material and aging
condition) had an influence on bond strength of fiber posts to resin cement
and flowable composite leading to the rejection of the null hypotheses. It is
important to emphasise that the applied method is a simplified model of
accelerated aging (De Munck et al. 2005) which has been commonly
performed for challenging resin-dentin adhesion (Okuda et al. 2002; Reis et
al. 2004; Carrilho et al. 2005). Clinically, the post-composite bond in a
restored tooth cannot be directly exposed to the wet environment in a manner
comparable to an in vitro experimental design, which precludes a direct
correlation with the clinical conditions. In the present study, the observed
decrease in bond strength may be related only to the exposure to water of the
adhesive interface on the sticks, as the surface of the posts was not exposed.
In the clinical conditions a direct intraoral exposure of the post-composite
interface is routinely avoided by immediately restoring a tooth with a direct
composite restoration or a crown. In the case of crown placement, the core
material covers the post-composite interface protecting it during crown
fabrication. In the worst case scenario, assuming that the coronal restoration
fails in preventing leakage during clinical service, and that oral fluids
subsequently reach the post-composite interface, it is reasonable to assume
57
that it would take a considerably longer period of time for the fiber post-
composite bond to weaken. Despite of these limitations, the experimental set-
up employed in this study allowed to evaluate the effect of accelerated water
diffusion phenomena on the FRC post-cement/flowable composite interface
and the effectiveness of adhesive in preventing it within a shorter period of
time (De Munck et al. 2005).
Previous studies performed on the same epoxy resin-based fiber post
reported significantly higher bond strengths on adhesive-treated posts when
compared with no surface treatment (Aksornmuang et al. 2004;
Aksornmuang et al. 2006). All the posts tested in the present study were
treated with the same adhesive system, in order to evaluate whether the
enhanced immediate bond strength is unaffected by accelerated challenging
procedures. However, significantly lower bond strengths were recorded in all
groups after aging, regardless of previous sandblasting and the resinous
material that was placed on the posts. SEM evaluation supported bond
strength data, revealing gaps at the post-adhesive interface after aqueous
challenge. The mechanism involved may be related to the presence of
hydrophilic monomers in XPBond adhesive layer (Table 1), such as HEMA,
TEGDMA and TCB resin, which may be susceptible to water sorption
(Malacarne et al. 2006). The hydrophilicity of TEGDMA is explained by the
presence of hydrophilic ether linkages (Ferracane 2006), while TCB resin is a
reaction product between tetracarboxylic acid and HEMA, which contains
two carboxyl groups (Yap et al. 1998). Complex reactions that occur in
polymer networks exposed to the wet environment are related to water
sorption and solubility that affect their dimensions (Ferracane 2006).
Exposure to water was also reported to result in the formation of microcracks
in HEMA- containing polymer networks (Ghi et al. 2001; George et al. 2004)
depending on the concentration of HEMA (Ghi et al. 2001). The occurrence
58
of cracks was explained by stresses generated between the hydrated swollen
outer layer and the inner portions of the polymer, when water begins to
diffuse into the polymer network. Although self-healing and closing of the
cracks inside of the polymer is possible (Ghi et al. 2001), it can be assumed
that the interaction between these processes played a role in the gradual
separation at the interface between the fiber post and the adhesive.
Sandblasting of the posts prior to the adhesive application improved
only immediate bond strength. In the light of the overall reduction in bond
strength after accelerated aging, the role of sandblasting is probably of minor
importance if the posts are subsequently coated with a relatively hydrophilic
adhesive. It is possible that FRC post-composite bonds mediated by
sandblasting alone would not be affected by the detrimental effect of water,
being the adhesion mechanism mediated only by a physical interaction
between components. Another potential approach to avoid the concern
related to hydrophilicity of adhesives or silane solutions would be the use of
more hydrophobic industrial coatings. In a similar experimental design as in
the present study, industrially coated FRC posts resulted in immediate bond
strengths that were lower if compared to XPBond adhesive treatment, but
were not affected by one month accelerated water aging (Zhang et al,
unpublished results).
59
Conclusions
The investigated dual-cured resin cement exhibited higher bond strength to
fiber posts than flowable composite when the groups with the same post
surface treatment were compared, both immediately and after 1 month.
Sandblasting followed by adhesive application may improve immediate bond
strength in comparison to the adhesive alone. After accelerated water aging
the two post surface treatments resulted in comparable bond strengths. Fiber
post-resin cement and fiber post-flowable composite bonds may be impaired
by accelerated water aging if mediated by hydrophilic adhesive coatings.
60
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Monticelli F, Toledano M, Tay FR, Sadek FT, Goracci C, Ferrari M
(2006b). A simple etching technique for improving the retention of fiber
posts to resin composites. J Endod 32(1): 44-7.
Okuda M, Pereira PN, Nakajima M, Tagami J, Pashley DH (2002).
Long-term durability of resin dentin interface: nanoleakage vs. microtensile
bond strength. Oper Dent 27(3): 289-96.
Pashley DH, Carvalho RM, Sano H, Nakajima M, Yoshiyama M,
Shono Y, Fernandes CA, Tay F (1999). The microtensile bond test: a review.
J Adhes Dent 1(4): 299-309.
Perdigao J, Gomes G, Lee IK (2006). The effect of silane on the bond
strengths of fiber posts. Dent Mater 22(8): 752-8.
Pirani C, Chersoni S, Foschi F, Piana G, Loushine RJ, Tay FR, Prati
C (2005). Does Hybridization of Intraradicular Dentin Really Improve Fiber
Post Retention in Endodontically Treated Teeth? J Endod 31(12): 891-894.
63
Radovic I, Monticelli F, Goracci C, Cury AH, Coniglio I, Vulicevic
ZR, Garcia-Godoy F, Ferrari M (2007). The effect of sandblasting on
adhesion of a dual-cured resin composite to methacrylic fiber posts:
Microtensile bond strength and SEM evaluation. J Dent 35(6): 496-502.
Reis A, Loguercio AD, Carvalho RM, Grande RH (2004). Durability
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component. Dent Mater 20(7): 669-76.
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I (2006). Microleakage along Glassix glass fibre posts cemented with three
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363-7.
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surface treatment of prefabricated posts on bonding of resin cement. Oper
Dent 29(1): 60-8.
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64
2.3. Coupling of composite resin cements to quartz fiber post: a
comparison of industrial and “chair-side” treatments of the post surface
Ivana Radovic, Francesca Monticelli, Àlvaro Hafiz Cury, Egidio Bertelli,
Zoran R. Vulicevic, Marco Ferrari. Journal of Adhesive Dentistry 2008;
10(1): 57-66.
Introduction
Since their introduction back in 1990’s (Duret et al. 1990), fiber post and core
systems have been extensively investigated (Schwartz and Robbins 2004;
Schwartz and Fransman 2005). In vitro studies have demonstrated the
advantages of these systems over conventional cast posts or prefabricated
metallic posts (Martinez-Insua et al. 1998; Sirimai et al. 1999; Cormier et al.
2001; Akkayan and Gulmez 2002; Newman et al. 2003; Fokkinga et al.
2004; Hayashi et al. 2006). The satisfactory clinical performance of fiber
post and core systems has been reported in short or medium-term clinical
studies (Fredriksson et al. 1998; Ferrari et al. 2000a; Glazer 2000; Malferrari
et al. 2003; Naumann et al. 2005; Naumann et al. 2005). Conversely, a recent
retrospective long-term study reported shorter survival times for carbon fiber
reinforced epoxy resin posts than those previously documented for cast posts
(Segerstrom et al. 2006). In some clinical studies debonding of the post was
frequently observed as the main failure mode (Ferrari et al. 2000b; Mannocci
et al. 2002; Monticelli et al. 2003; Cagidiaco et al. 2007) , which may
question the real efficacy of the employed adhesive procedures. Fiber post
placement involves the formation of two equally important interfaces both at
the dentin/resin composite and resin composite/fiber level where a failure can
eventually occur. The achievement of an optimal coupling at the interfaces is
65
considered to be crucial for ensuring the restoration homogeneity and
durability, as well as for favorable stress distribution (De Santis et al. 2000).
In a recently published investigation on luting fiber posts to
hybridized root canals, 60% of the failures during push-out testing occurred
between the fiber post and the cement (Perdigao et al. 2006). Various post
surface “chair-side” treatments have been recommended with the purpose of
enhancing the adhesion of resin cements and different resin based core
materials to fiber posts. Hydrogen peroxide etching and chemical
pretreatment with potassium permanganate followed by silanization
increased bond strength to flowable composites (Monticelli et al. 2006b;
Monticelli et al. 2006c). Adhesion of composite resins to quartz fiber posts
was improved when the post surface was treated with a bonding agent
(Aksornmuang et al. 2004; Aksornmuang et al. 2006) or was silanized
(Aksornmuang et al. 2004; Aksornmuang et al. 2006; Monticelli et al. 2006a;
Magni et al. 2007). Sandblasting followed by silane coating (Sahafi et al.
2003) and sandblasting alone (Sahafi et al. 2003; Radovic et al. 2007)
significantly increased bond strength of resin cements to glass fiber posts.
Adhesion to fiber posts may also be improved by the use of tribochemical
systems which allow the creation of chemical bonds between non-ceramic
surfaces and resin composites (Sahafi et al. 2003; Sahafi et al. 2005;
Valandro et al. 2006). However, both laboratory (Rocatec, 3M ESPE) and
intraoral (CoJet, 3M ESPE) tribochemical systems consist of three
components that need to be successively applied. Therefore, an industrial
employment of the fiber post surface treatment that would eliminate the need
for additional chair-side treatments may be advantageous, allowing for a
simplification of the clinical procedures.
An experimental patented industrial treatment has been recently
developed with the intention of improving post-composite coupling.
66
According to the manufacturer’s information, the treatment comprises two
main steps: a 1�m-thick coating of zirconium oxide followed by silanization
with 3–(trimethoxysilyl) propyl methacrylate. This treatment is claimed to
keep the initial surface roughness of the fiber post in order to provide
micromechanical retention and to create a chemical bond between the silane
and the adhesive or cement. Electrolitically deposited zirconium oxide
coatings on dental cobalt-chromium alloys prevent corrosion and release of
metal ions (Hsu and Yen 1998). Zirconium oxide sandblasting was used to
treat the surface of titanium endosseus dental implants (Franchi et al. 2004).
However, no information is available on the potential application of
zirconium oxide coatings on fiber post surface.
The aim of this investigation was to evaluate the influence of an
industrial treatment and conventional “chair-side” treatments of fiber post
surface on the microtensile bond strength to luting resin cements. The null
hypothesis tested is that the treatment of the post surface does not influence
the bond strength of fiber posts to dual cured resin cements.
Materials and methods
Forty-two translucent quartz fiber posts (Light Post, RTD) with a diameter of
1.8mm were used in the study. Posts were divided into 7 groups (n=6)
according to the surface treatment performed. Groups I and II: experimental
patented industrial treatment consisting of a coating with a layer of zirconium
oxide followed by silanization with a 3–(trimethoxysilyl)propyl methacrylate
(RTD, St Egrève, France). Group III: industrial coating (the same as in
groups I and II, RTD) followed by etch-and-rinse adhesive application
(XPBond, Dentsply Caulk, Milford, DE, USA). Group IV: adhesive
application (XPBond). Group V: adhesive application (Prime&Bond NT,
67
Dentsply Caulk). Group VI: silane application (Calibra Silane, Dentsply
Caulk). Group VII: no treatment (control group). The materials were used
according to the manufacturers’ instructions; their chemical composition,
batch numbers and application modes are reported in Table 1. Both adhesives
were used in the self-cure mode.
Coupling of resin cements and microtensile test procedures
Two resin cements (Sealbond, RTD – Group I and Calibra, Dentsply Caulk –
Groups II to VII) were applied on the posts to produce cylindrical specimens
with the post in the center, using a transparent plastic matrix. A procedure
previously described by Goracci et al. for core build-up materials was
followed (Goracci et al. 2005). All specimens were prepared by a single
investigator to avoid the risk of operator’s variability. Each post was
positioned upright on a glass slab, and secured with a drop of sticky wax. A
cylindrical plastic matrix was placed around the post and adjusted so that the
post would be exactly in the middle (Figure 1). The matrix was 10 mm in
diameter. In height, the matrix was extended to the end of the coronal taper of
the post (about 10 mm). For an appropriate cutting of the microtensile
specimens, it is desirable that the post diameter is constant throughout the
post length. Since the coronal taper of Light Post is parallel sided, it was used
in its complete length.
68
Figure 1: Schematic drawing of specimen preparation for microtensile bond
strength testing. C: cement; P: post.
69
Table 1: Composition, batch numbers and the application mode of the
materials used in the study
Material Composition Application mode Prime & Bond NT adhesive (Dentsply Caulk) Batch no. 0501001760
Di- and Trimethacrylate resins, PENTA (dipentaerythritol penta acrylate monophosphate), Photoinitiators, Stabilizers, Nanofillers - Amorphous Silicone Dioxide, Cetylamine hydrofluoride, Acetone
Mix Prime&Bond NT (XPBond) adhesive with Self-Cure Activator (1:1); apply mixture to the post surface for 1-2 s; gently air dry.
XPBond adhesive (Dentsply Caulk) Batch no. 0503004020
carboxylic acid modified dimethacrylate (TCB resin), phosphoric acid modified acrylate resin (PENTA), urethane dimethacrylate (UDMA), triethyleneglycol dimethacrylate (TEGDMA), 2-hydroxyethylmethacrylate (HEMA), Butylated benzenediol (stabilizer), ethyl-4-dimethylaminobenzoate, camphorquinone, functionalised amorphous silica, tertiary butanol
Self-cure activator (Dentsply Caulk) Batch no. 040901
Aromatic Sodium Sulfinate, (Self cure initiator), Acetone, Ethanol
Calibra Silane Coupling Agent (Dentsply Caulk) Batch no. 0503242
Acetone; Ethyl Alcohol; Organo Silane Treat the post surface with the silane; air dry.
Calibra Esthetic Resin Cement (Dentsply Caulk) Batch no. 050412 Batch no. 0506142
Base: Dimethacrylate Resins; Camphorquinone (CQ) Photoinitiator; Stabilizers; Glass Fillers; Fumed silica; Titanium Dioxide; Pigments Catalyst: Dimethacrylate Resins; Catalyst; Stabilizers; Glass Fillers; Fumed Silica Mix cement
components; seat the post immediately; light cure.
Sealbond Resin Cement (RTD St Egreve France) Batch no. 01379200511
Base: Bis-GMA, Hexane diol dimethacrylate, Camphorquinone; Stabilizers; Barium glass fillers; Silica; Pigments Catalyst: Bisgma, Hexane diol dimethacrylate, Peroxide, Stabilizers; Barium glass fillers; Silica; Pigments
Light Post (RTD St Egreve France) Batch no. 00210200504 Batch no. 05/65 (ind. treatment)
Epoxy resin (40%); quartz fibers (60%) Industrial treatment: coating with a layer of zirconium oxide followed by silanisation with a 3–(trimethoxysilyl)propyl methacrylate.
-
70
The resin cements were mixed, applied on the post filling the matrix
completely, and light cured for 40 s with a halogen curing light (600 mW/cm2
output; VIP; Bisco, Schaumburg, IL, USA) directly from the open upper side
of the matrix and through the post. Additional 40 s irradiations were
performed from each side of the cylinder prior to the removal of the matrix to
ensure optimal polymerization of the cement material. The sectioning and
loading of the specimens began on completion of the cementation procedure,
in order to simulate the clinical situation of immediate loading applied in the
procedures of core preparation, impression, and temporary crown adaptation
and cementation.
The cylinders were mounted in a cutting machine (Isomet 1000,
Buehler, Lake Bluff, IL, USA) and sectioned under water cooling to obtain a
slab of uniform thickness, with the post in the center and the cement build-up
on each side. Six to eight sticks of 1-mm in thickness were obtained from
each slab, resulting in multiple specimens (33 per group) that were available
for microtensile bond strength testing. During the experimental industrial
coating procedure, 3mm at the coronal end of the post were not coated.
Therefore, sticks obtained from this part of the post in groups I-III were
excluded. Sticks were glued (Super Attak Gel, Henkel Loctite Adesivi S.r.l.,
Milano, Italy) to the two free sliding components of a jig, which was
mounted on a universal testing machine (Triax, Controls S.P.A., Milano.
Italy) and loaded in tension at a crosshead speed of 0.5 mm/min until failure
occurred at either side of the post-composite interface. Failure modes were
evaluated with a stereomicroscope (Nikon SMZ645) at 40x magnification
and recorded as adhesive (at the post/cement interface), cohesive (within the
post or the cement) or mixed (a combination of the two modes of failure in
the same interface). Bond strength values were expressed in MegaPascals
(MPa), dividing the load at failure in Newtons by the bonding surface area.
71
As the bonded interface was curved, its area was calculated using a
mathematical formula previously applied by Bouillaguet et al. (Bouillaguet et
al. 2003). Nine beams from group VI and eleven beams from group VII failed
prematurely during the cutting procedure. For each of the prematurely failed
beams bond strength value was recorded as 0 MPa and included in the
statistical analysis.
SEM evaluation
One sample from each group was randomly chosen for scanning electron
microscopic evaluation (SEM) of the fiber post-cement interface. The
cylinders were cut into 1.5mm thick cross sections (Isomet 1000). Sections
were polished with wet abrasive SiC papers, cleaned with 37%
orthophosphoric acid for 15 seconds, rinsed with water, ultrasonicated in
96% ethanol for 2 min and air dried. Each slice was mounted on a metallic
stub, sputtered with gold-palladium (Polaron Range SC7620; Quorum
Technology, Newhaven, UK), and observed under a SEM (JSM 6060 LV,
JEOL, Tokyo, Japan) at different magnifications, using secondary electron
beam. Additionaly, back scattered mode was used to observe the post-cement
interfaces on industrialy coated posts. Four additional fiber posts were
examined with a scanning electron microscope in order to detect differences
in the surface texture between industrially coated (n=2) and conventional
posts (n=2). One industrially coated and one conventional post were observed
longitudinally, while the remaining two were cross-sectioned with a diamond
saw (Isomet 1000) and polished with wet abrasive SiC papers. The specimens
were rinsed in deionised water, air-dried, gold-sputtered (Polaron Range
SC7620) and observed under a scanning electron microscope (JSM 6060
LV). The surface of the industrialy coated posts was also examined using
72
Energy Dispersive Analysis by X-ray (EDAX) in a scanning electron
microscope.
Statistical analysis of the microtensile bond strength data
A preliminary linear regression analysis showed that the post–cement
cylinder did not have a significant influence on the measured bond strength;
therefore, the sticks were considered as independent within each group. Since
the bond strength data were not normally distributed (Kolmogorov–Smirnov
test, p>0.05), a Kruskal-Wallis analysis of variance was performed with bond
strength as the dependent variable, and the type of surface treatment as the
factor. Dunn’s multiple range test for was used for the post-hoc comparisons.
The level of significance was set at p<0.05 and calculations were handled
by the SPSS 13.0 software (SPSS Inc.; Chicago, IL, USA).
Weibull analysis was performed to determine failure probability at
specific loads, Weibull modulus (m) and characteristic bond strength (�; the
strength at the failure probability of 63.2%) in the experimental groups. The
calculations were handled by the Weibull++ 7 software (ReliaSoft
Corporation, Tucson, AZ, USA).
Results
Interfacial Bond Strength
The post surface treatment significantly influenced the measured bond
strengths (p<0.001). Significantly higher bond strengths (p<0.001) were
achieved in Groups I, II and III, when the industrial treatment was performed,
and in Group IV, when the surface was treated with the XPBond adhesive
(Figure 2). Additional adhesive application did not influence bond strength
on industrially coated posts (Group III). No significant differences between
73
the two tested luting cements were recorded. Bond strengths to silanized
(group VI) and no treated fiber posts (Group VII) were the lowest (p<0.001)
and comparable. The application of Prime&Bond NT adhesive resulted in
significantly higher bond strengths compared to no treatment and
silanization, but lower than in groups I-IV.
The data were shown to fit a 2-parameter Weibull distribution curve.
Probability of failure as a function of stress, Weibull modulus (m) and
characteristic bond strength (�) are shown in Figure 3. The lowest probability
of failure was found in groups I-IV (industrialy treated and XPBond coated
posts), followed by groups V (Prime & Bond NT), VI (Calibra Silane) and
VII (no treatment).
During microtensile testing, the recorded failure mode in Groups I-III
and V-VII was 100% adhesive in nature. In Group IV, six beams (20%)
failed cohesively within the post, and one beam (3%) failed cohesively within
luting cement.
SEM evaluation
Cross-sections of the post-cement interfaces revealed a good adaptation of
the resin cements to the post surface in all groups. No defects and no
discontinuities occurred along the interface between the fiber post and the
cement. An intimate contact of quartz fibers with the resin cement was
frequently observed along the interface in all groups. No significant
differences in the morphology of the interface between the groups were
noticed (Figure 4). In back scattered mode, tight adaptation of the cement to
industrialy coated post surface was visible (Figure 5). A uniform coating
could be seen both at the low magnification (Figure 5A; x500) and high
magnification (Figure 5B; x5000).
74
Figure 2: Post-cement microtensile bond strength. The length of each box
represents the interquartile range of microtensile bond strengths. The ends of
the box are the upper and lower quartiles. A horizontal line inside the box
marks the median. The whiskers extend to the highest and lowest
microtensile bond strengths. Different letters in brackets indicate statistically
significant differences. IND: Industrial treatment; SEAL: Sealbond cement;
CAL: Calibra cement; XPB: XPBond adhesive; PBNT: Prime&Bond NT
adhesive; SIL: Calibra Silane; NO: No treatment.
IND/SEAL (A)IND/CAL (A)
IND+XPB/CAL (A)XPB/CAL (A)
PBNT/CAL (B)SIL/CAL (C)
NO/CAL (C)
0
10
20
30
40
[MPa
]
75
Figure 3: Weibull distribution plots of a probability of failure as a function of
stress. m: Weibull modulus; �: characteristic bond strength (the strength at
the failure probability of 63.2%).
76
B
A
Figure 4: SEM images of the post-cement interfaces. Tight and continuous
adaptation of the cement to the post surface can be seen, with a frequent
occurrence of direct contact between the fibers and the cement. A: SEM
image of the interface between industrially treated fiber post and Sealbond
cement; B: SEM image of the interface between conventional fiber post
treated with XP Bond adhesive and Calibra cement.
77
Figure 5: Images of the post-cement interface between Calibra cement and
industrialy coated posts made using back scattered mode. Tight adaptation of
the cement to post surface and a uniform coating are visible both at the low
magnification (A; x500) and high magnification (B; x5000).
B
A
78
Fiber post surface observation revealed a modification of the surface
morphology of industrially coated fiber posts (Figure 6A, 6B) when
compared to conventional posts (Figure 6C). A uniform coating was visible
on industrially treated posts.
Figure 6: SEM images
of the fiber post
surface prior to
performing the build-
up. A fairly uniform
coating is visible on
industrially treated
posts (A). B: The
transition (arrow)
between the coronal
end of the post (not
treated) and the
experimental industrial
coating; C: surface of a
conventional quartz
fiber post.
B
C
A
79
B
A
Cross-sectional views of industrially coated (Figure 7A) and conventional
post (Figure 7B) revealed that the action of the industrial treatment resulted
in partial removal of the resin matrix and impregnation of the exposed quartz
fibers with the coating (Figure 7A).
Figure 7: Cross-sectional views of industrially coated (A) and conventional
fiber post (B). The resin matrix was partialy removed from the post surface
by the industrial treatment (A); the coating covers the exposed quartz fibers
(arrow). The uniformity and integrity of the coating may have been affected
by polishing during the sample preparation.
80
The EDAX revealed the presence of zirconium, silicon, oxygen, calcium,
carbon and natrium (Figure 8). Zirconium and silicon were the predominant
elements.
Figure 8: EDAX of the industrialy treated fiber post surface revealed the
presence of zirconium, silicon, oxygen, calcium, carbon and natrium.
81
Discussion
Significant differences in bond strengths were found between the
experimental groups. Both industrial coating and adhesive application
resulted in a superior outcome than silanization or no treatment of the fiber
post surface. Therefore, the null hypothesis was rejected.
The highest post-to-cement bond strengths were recorded on
industrially coated fiber posts. The experimental treatment performed was
still under development at the time this investigation was conducted.
However, general information on its composition was available from the
manufacturer (Table 1). The chemical nature of the industrial coating was
determined using Energy Dispersive Analysis by X-ray in a scanning electron
microscope and these findings correlated with the manufacturer’s information
(Figure 8). The industrial employment of zirconium oxide coating followed
by silanization to create fiber post surface coatings seems promising, as it
may simplify the clinical procedures during post cementation. The two
investigated resin cements, Sealbond and Calibra, achieved comparable bond
strengths to industrialy coated posts. It would also be of interest to investigate
whether similar results could be obtained with different types of luting
cements, such as resin modified glass ionomers and/or self-adhesive cements.
Significantly higher bond strengths were also obtained by the
application of the tested etch-and-rinse adhesive systems used in the self-cure
mode (Prime&Bond NT and XPBond) when compared to the control group.
This finding supports previous investigations conducted on the same type of
fiber post (Aksornmuang et al. 2004; Aksornmuang et al. 2006).
Enhancement of composite to composite bond strength was also reported
when adhesives were used as intermediate layers in composite repair
procedures (Saunders 1990; Shahdad and Kennedy 1998; Tezvergil et al.
82
2003). One of the explanations for the enhanced post-cement bond strength
may be the low viscosity of adhesive and a small contact angle that facilitates
micromechanical retention by penetration of monomer components into
microiregularities of the post surface. Furthermore, adhesive application may
have improved surface wettability resulting in a better distribution of the
resin cements. An interesting observation is the superior performance in
terms of bond strength of the new adhesive XPBond when compared to
Prime&Bond NT, resulting comparable to industrial treatment. It is possible
that the presence of a different solvent in XPBond (tertiary butanol instead of
acetone) influenced its wetting properties and consequently coupling with
fiber post surface. According to the manufacturer’s information, tertiary
butanol is for the first time employed in clinical dentistry as the solvent in
XPBond adhesive. Thanks to its high solvation forces (Pashley et al. 2002) it
is claimed to increase the resin content of bonded interfaces. It may be
speculated that better evaporation of buthanol increased resin concentration,
wettability and adaptation of the resin cement to the post surface. These
properties might have played a role in the favorable post-cement bond
strength recorded by XPBond. Both tested adhesives were used in the self-
curing mode, thus a frank adhesive layer was not visible at the post-cement
interfaces and its thickness could not have been determined (Figure 4B).
The beneficial effect of adhesive observed in the present study is in
contrast with the investigation of Ferrari et al. (Ferrari et al. 2006) that
reported no improvement in fiber post-core bond strength after coating the
methacrylate resin-based post with different adhesives. However, the matrix
of Light Post is epoxy resin-based, which may have accounted for the
disagreement in the results. Artopoulou et al. have shown that the effect of
adhesive coating on post retention depended on the core material placed
around the fiber post (Artopoulou et al. 2006). It may be speculated that the
83
effect of adhesive depends on the type of fiber post, type of core
material/resin cement and type of adhesive. This topic deserves further
research.
Although adhesive application significantly improved bond strength
compared to control group, it did not further increase bond strength on
industrially treated posts (Group IV). The industrial treatment induced
micromechanical and chemical changes in the surface of the posts (Figure
5A). The zirconium oxide coating followed by silanization apparently
improved the surface wettability to a sufficient extent, eliminating the need
for additional adhesive application, and at the same time offered sites
available for chemical bonding with the resin monomers.
The lowest bond strengths were recorded in the silanized post group
and when no treatment was performed. Moreover, premature failures were
observed in these two groups only, indicating an unfavorable post-cement
coupling. Although silanization tended to increase bond strength compared to
no treatment (Table 2, Figures 2 and 3), the difference was not statistically
significant. Sahafi et al. (Sahafi et al. 2003) reported that silanization did not
improve bond strength between fiber posts and resin cements unless it was
preceded by sandblasting, and this finding is consistent with the results of the
present study. The external surface of Light Post is mainly covered by epoxy
resin (Figure 6C). It can be assumed that previous surface treatment which
would expose the fibers would increase the surface available for chemical
bonding with the alcoxy groups of the silane molecules, and therefore result
in increased post-cement bond strength. Conversely, beneficial influence of
silanization without preceding sandblasting was demonstrated in
investigations of other authors that used DT Light Post (Aksornmuang et al.
2006; Monticelli et al. 2006a). Nevertheless, the silane applied in these
investigations was a two-component silane/adhesive system in which the
84
silane molecule is hydrolyzed “on demand” when mixed with the acidic
phosphate monomers which are present in water-containing dentin adhesives,
while in a present study a prehydrolized single-component silane was used.
The different strategy of the tested coupling agents may explain the
discrepancy with the results of the present investigation.
The cement layer that was placed around fiber posts was noticeably
thicker than the layer that formes in the root canal in a clinical situation. It
was recently demonstrated that different core diameters did not affect
retention values of glass fiber posts (Artopoulou et al. 2006). Nevertheless,
this limitation of the experimental set-up may have influenced the bond
strength results obtained. Higher values of Weibull modulus indicate systems
in which values of tensile strength show higher consistency, while low values
indicate systems with large data variability and are characteristic for brittle
materials. The Weibull moduli were generally low for all the materials tested.
This might indicate the need for additional methods for assessing the quality
of post-cement interfaces. Sectioning and loading of the specimens was
performed immediately after the cementation procedure with the intention of
assessing interfacial strength at the time when procedures of core preparation,
impression, and temporary crown adaptation/cementation are carried out.
Further investigations need to be conducted in order to assess the durability
of fiber post-composite bonds in clinical and accelerated aging conditions, as
well as the fatigue and fracture resistance of teeth restored with industrially
coated posts.
85
Conclusions
The experimental industrial surface treatment and the adhesive application
enhanced fiber post to resin cement interfacial strength. Industrial treatment
may simplify the clinical luting procedure. Cementation of epoxy resin-based
fiber posts without any treatment of the post surface is not recommended.
86
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canal dentin. Dent Mater 19(3): 199-205.
Cagidiaco MC, Radovic I, Simonetti M, Tay F, Ferrari M (2007).
Clinical performance of fiber post restorations in endodontically treated
teeth: 2-year results. Int J Prosthodont 20(3): 293-8.
Cormier CJ, Burns DR, Moon P (2001). In vitro comparison of the
fracture resistance and failure mode of fiber, ceramic, and conventional post
systems at various stages of restoration. J Prosthodont 10(1): 26-36.
De Santis R, Prisco D, Apicella A, Ambrosio L, Rengo S, Nicolais L
(2000). Carbon fiber post adhesion to resin luting cement in the restoration of
endodontically treated teeth. J Mater Sci Mater Med 11(4): 201-6.
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Duret B, Reynaud M, Duret F (1990). [New concept of
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Ferrari M, Goracci C, Sadek FT, Monticelli F, Tay FR (2006). An
investigation of the interfacial strengths of methacrylate resin-based glass
fiber post-core buildups. J Adhes Dent 8(4): 239-45.
Ferrari M, Vichi A, Garcia-Godoy F (2000a). Clinical evaluation of
fiber-reinforced epoxy resin posts and cast post and cores. Am J Dent
13(Spec No): 15B-18B.
Ferrari M, Vichi A, Mannocci F, Mason PN (2000b). Retrospective
study of the clinical performance of fiber posts. Am J Dent 13(Spec No): 9B-
13B.
Fokkinga WA, Kreulen CM, Vallittu PK, Creugers NH (2004). A
structured analysis of in vitro failure loads and failure modes of fiber, metal,
and ceramic post-and-core systems. Int J Prosthodont 17(4): 476-82.
Franchi M, Bacchelli B, Martini D, Pasquale VD, Orsini E, Ottani V,
Fini M, Giavaresi G, Giardino R, Ruggeri A (2004). Early detachment of
titanium particles from various different surfaces of endosseous dental
implants. Biomaterials 25(12): 2239-46.
Fredriksson M, Astback J, Pamenius M, Arvidson K (1998). A
retrospective study of 236 patients with teeth restored by carbon fiber-
reinforced epoxy resin posts. J Prosthet Dent 80(2): 151-7.
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carbon fibre posts--a prospective study. J Can Dent Assoc 66(11): 613-8.
Goracci C, Raffaelli O, Monticelli F, Balleri B, Bertelli E, Ferrari M
(2005). The adhesion between prefabricated FRC posts and composite resin
cores: microtensile bond strength with and without post-silanization. Dent
Mater 21(5): 437-44.
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Hayashi M, Takahashi Y, Imazato S, Ebisu S (2006). Fracture
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corrosion resistance of ZrO2 thin coatings on the dental Co-Cr alloys. Dent
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I, Ferrari M (2007). Adhesion between fiber posts and resin luting agents: a
microtensile bond strength test and an SEM investigation following different
treatments of the post surface. J Adhes Dent 9(2): 195-202.
Malferrari S, Monaco C, Scotti R (2003). Clinical evaluation of teeth
restored with quartz fiber-reinforced epoxy resin posts. Int J Prosthodont
16(1): 39-44.
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Three-year clinical comparison of survival of endodontically treated teeth
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of the fracture resistances of pulpless teeth restored with a cast post and core
or carbon-fiber post with a composite core. J Prosthet Dent 80(5): 527-32.
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behavior of translucent-fiber posts: a 2-year prospective study. Int J
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(2006b). Post-surface conditioning improves interfacial adhesion in post/core
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Monticelli F, Toledano M, Tay FR, Sadek FT, Goracci C, Ferrari M
(2006c). A simple etching technique for improving the retention of fiber
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strengths of fiber posts. Dent Mater 22(8): 752-8.
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Microtensile bond strength and SEM evaluation. J Dent 35(6): 496-502.
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Chapter 3: Selection of resin cement for fiber post cementation
3.1. Self-adhesive resin cements: a literature review
Ivana Radovic, Francesca Monticelli, Cecilia Goracci, Zoran R. Vulicevic,
Marco Ferrari. Journal of Adhesive Dentistry 2008; 10(4): 251-258.
Introduction
The clinical success of an indirect restorative procedure depends in part on
the cementation technique used to create a link between the restoration and
the tooth. The different luting cements that are available to the clinicians
have been categorized into five main classes: zinc phosphate cements,
polycarboxylate cements, glass ionomer cements, resin-modified glass
ionomer cements and resin composite cements (Diaz-Arnold et al. 1999).
Although each of the five classes has been widely investigated, the correct
clinical choice between them is not always clear (Rosenstiel et al. 1998).
None of the five cement types is suitable to be used for the entire broad range
of indirect restorative procedures. Therefore, their proper application requires
a thorough understanding and awareness of each material’s advantages and
disadvantages, taking into account the restorative material, moisture control
and preparation design (retentive or adhesive) (Diaz-Arnold et al. 1999).
Until recently resin cements were divided into two subgroups
according to the adhesive system used to prepare the tooth prior to
cementation. One group utilizes etch-and-rinse adhesive systems (e.g.
Variolink and Variolink II, Ivoclar-Vivadent, Schaan, Lichtenstein; Calibra,
Dentsply Caulk, Milford, DE, USA; Nexus, Kerr, Orange, CA, USA). In the
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other group, enamel and dentin are prepared using self-etching primers (e.g.
Panavia 21, Panavia F and Panavia F 2.0, Kuraray Medical Inc., Tokyo,
Japan; Multilink, Ivoclar-Vivadent). Self-adhesive cements were introduced
in 2002 as a new subgroup of resin cements (e.g. RelyX Unicem, 3M ESPE,
St. Paul, MN, USA). These materials were designed with an intention to
overcome some of the shortcomings of both conventional (zinc phosphate,
polycarboxylate and glass ionomer cements) and resin cements, as well as to
bring the favorable characteristics of different cement classes into a single
product.
Self-adhesive cements do not require any pretreatment of the tooth
surface. Once the cement is mixed, its application procedure is extremely
simple. Application is accomplished through a single clinical step, similarly
to the application procedures of zinc-phosphate and polycarboxylate cements.
According to the manufacturers’ information, as the smear layer is not
removed, no post-operative sensitivity is expected. Unlike zinc phosphate,
polycarboxylate and resin cements, self-adhesive cements are claimed to be
moisture tolerant and to release fluoride ions in a manner comparable to glass
ionomer cements. Furthermore, they are expected to offer esthetics, optimal
mechanical properties, dimensional stability and micromechanical adhesion,
analogous to resin cements. Such a combination of favorable features of
conventional and resin cements is claimed to render self-adhesive cements
suitable for a wide range of applications. At the same time, the clinicians’
demands for simplification of luting procedures are addressed, as the
application procedure purportedly leaves little or no room for mistakes
induced by technique sensitivity.
Self-adhesive cements are still relatively new and detailed
information on their composition and adhesive properties is limited.
Although the basic adhesion mechanism appears to be the same for all self-
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adhesive cements, features of RelyX Unicem (3M ESPE) are by far the most
extensively explained by the manufacturer (3M ESPE product profile; RelyX
Unicem). This cement was the first product from the class of self-adhesive
cements to be introduced to the market. Its multifunctional monomers with
phosphoric acid groups simultaneously demineralize and infiltrate enamel
and dentin. The dominant setting reaction is the radical polymerization that
can be initiated by light exposure or through the self-cure mechanism. This
results in extensive cross linking of cement monomers and the creation of
high molecular weight polymers. Additionally, in order to assure
neutralization of this initially acidic system, a glass ionomer concept was
applied, resulting in the pH increase from 1 to 6 through reactions between
phosphoric acid groups and alkaline filer. Phosphoric acid groups also react
with the tooth apatite. Water that is formed in these neutralization processes
is claimed to contribute to cement’s initial hydrophylicity, which provides
improved adaptation to the tooth structure and moisture tolerance.
Subsequently, water is expected to be reused by reaction with acidic
functional groups and during the cement reaction with ion-releasing basic
filler particles. Such a reaction would finally result in an intelligent switch to
a hydrophobic matrix. The adhesion obtained is claimed to rely on
micromechanical retention and chemical interaction between monomer acidic
groups and hydroxyapatite.
Several products are currently available on the market (Table). They
differ in terms of delivery systems, working/setting times, number of
available shades and composition. According to the manufacturers, all
currently available self-adhesive cements release fluoride ions. All these
products are dual-cured radiopaque materials that are indicated for adhesive
cementation of virtually any indirect restoration: ceramic, composite, metal,
inlays (composite or metal), onlays, bridges, crowns, posts and screws
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(including fiber posts) made of metal, composite and ceramic. The only
procedure in which the use of self-adhesive cements is not indicated is the
cementation of veneers. In this case light curing veneer cements are
recommended, as the practitioners usually require longer working time that
allows the positioning and adjustment of several veneers simultaneously,
prior to light initiation of the cement polymerization.
This literature review aimed at summarizing research conducted on
self-adhesive cements and at providing information on their properties, based
on the results of original scientific full-papers from peer-reviewed journals
listed in PubMed. The search was conducted using the term: self-adhesive
cement OR biscem OR gcem OR wetbond OR maxcem OR monocem OR
multilink sprint OR unicem.
Literature data
RelyX Unicem is undoubtedly the most thoroughly investigated self-adhesive
cement in the current literature. The vast majority of the articles published in
Medline cited journals investigated some of the properties of this cement.
Limited information is also available on Maxcem (Bishara et al. 2006a;
Goracci et al. 2006; Frankenberger et al. 2007), while no studies that
investigated other currently marketed self-adhesive cements have been
published so far. One study assessed the handling properties of Relyx
Unicem in clinical use through a practice-based evaluation (Burke et al.
2006). All the other published articles are based on in vitro investigations.
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Table: Features of commercially available self-adhesive cements
Product Working / setting time Composition BisCem (Bisco Inc, Schaumburg, IL, USA)
1min / 6min at 22°C (72°F)
Bis (Hydroxyethyl methacrylate) phosphate (Base) Tetraethylene glycol dimethacrylate Dental Glass
Breeze Pentron Clinical Technologies, Wallingford, CT, USA
(information not available)
Mixture of BisGMA, UDMA, TEGDMA, HEMA, & 4-MET resins, silane-treated bariumborosilicate glasses, silica with initiators, stabilizers and UV absorber, organic and/or inorganic pigments, opacifiers
GCem GC Corp, Tokyo, Japan
2min / 4min (based on oral temperature)
Powder: fluoro-alumino-silicate glass, initiator, pigment Liquid: 4-MET, phosphoric acid ester monomer, water, UDMA, dimethacrylate, silica powder, initiator, stabilizer
Embrace WetBond resin cement (Pulpdent, Watertown, MA, USA
completely auto-cures in 7 minutes
(information not available)
Maxcem (Kerr; Orange, CA, USA)
gel time is 2 minutes – set time is 3 minutes (based on oral temperature)
GPDM (glyceroldimethacrylate dihydrogen phosphate), comonomers (mono-, di-, and tri-functional methacrylate monomers), proprietary self-curing redox activator, photoinitiator (camphorquinone), stabilizer, barium glass fillers, fluoroaluminosilicate glass filler, fumed silica (filler load 67% wt, particle size 3.6 μm)
MonoCem Shofu Dental Corporation, San Marcos, CA, USA
Unlimited working time. Completely auto-cures in 7 minutes in anaerobic conditions.
(information not available)
Multilink Sprint Ivoclar Vivadent, Schaan, Lichtenstein
Working time: 130+/-30s Setting time: 270+/-30s (based on oral temperature)
Dimethacrylates and acidic monomers. The inorganic fillers are barium glass, ytterbium trifluoride and silicon dioxide. The mean particle size is 5 μm. The total volume of inorganic fillers is approx. 48 %.
RelyX Unicem 3M ESPE, St. Paul, MN, USA
2min / 5min at 22°C (72°F)
Powder: glass fillers, silica, calcium hydroxide, self-curing initiators, pigments, light-curing initiators (filler load 72% wt, particle size <9.5 μm) Liquid: methacrylated phosphoric esters, dimethacrylates, acetate, stabilizers, self-curing initiators, light-curing initiators
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Adhesion to tooth substrates
Enamel
Self-adhesive cements adhesion to ground enamel was assessed in several
studies that evaluated bond strength (De Munck et al. 2004; Abo-Hamar et
al. 2005; Goracci et al. 2006; Hikita et al. 2007) and cement-enamel interface
micromorphology (De Munck et al. 2004; Goracci et al. 2006). Bond
strength of self-adhesive cements used for cementation of orthodontic
brackets to unground enamel was also investigated (Vicente et al. 2005;
Bishara et al. 2006a; Bishara et al. 2006b). In all the studies self-adhesive
cements were light cured.
Bond strength of RelyX Unicem (De Munck et al. 2004; Abo-Hamar
et al. 2005; Goracci et al. 2006; Hikita et al. 2007) and Maxcem (Goracci et
al. 2006) to enamel was investigated using shear (Abo-Hamar et al. 2005)
and microtensile (De Munck et al. 2004; Goracci et al. 2006; Hikita et al.
2007) bond strength tests. Shear bond strength of RelyX Unicem to enamel
was evaluated prior and after thermocycling (Abo-Hamar et al. 2005). Before
thermocycling this cement produced bond strength of 14.5 MPa which was
significantly lower than the bond strengths of other resin luting systems
investigated, that ranged between 17 and 32 MPa. Moreover, its shear bond
strength to enamel was significantly lower after thermocycling, in contrast to
other resin cements that were not influenced by the same aging condition
(Abo-Hamar et al. 2005). However, since the bond strength of RelyX
Unicem was higher than the bond strength of a glass ionomer cement both
before and after thermocycling, it was pointed out that this self-adhesive
cement may be considered an alternative to glass ionomer cement for
cementation of high-strength ceramic or metal-based restorations. It was also
commented that RelyX Unicem may be used for luting conventional ceramic
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crowns with little or no enamel left, but that it might not be the ideal material
for luting inlays and partial crowns, if a considerable enamel surface area is
present (Abo-Hamar et al. 2005).
Similar results in terms of enamel bond strengths were reported in
microtensile bond strength investigations. Enamel microtensile bond
strengths of RelyX Unicem ranged between 10.7 MPa (Goracci et al. 2006)
and 19.6 MPa (De Munck et al. 2004; Hikita et al. 2007) and were
significantly lower compared to the bond strengths of self-etching cement
Panavia F 2.0 (De Munck et al. 2004; Goracci et al. 2006; Hikita et al. 2007)
and other resin cements (Hikita et al. 2007) that ranged between 25 and 49
MPa (De Munck et al. 2004; Goracci et al. 2006; Hikita et al. 2007).
Microtensile bond strength of Maxcem to enamel was significantly lower
compared to RelyX Unicem (Goracci et al. 2006). Conversely, RelyX
Unicem microtensile bond strength to enamel was comparable to other resin
cements when its application was preceded by phosphoric acid etching (De
Munck et al. 2004; Hikita et al. 2007).
Morphological evaluations revealed that RelyX Unicem should be
applied using some pressure in order to ensure its close adaptation to the
cavity wall (De Munck et al. 2004). However, the pressure twice as high as
the finger pressure had no effect on RelyX Unicem and other investigated
cements (Maxcem and Panavia F 2.0) microtensile bond strength to flat
ground enamel surfaces (Goracci et al. 2006). Under scanning electron
microscope, different self-adhesive cements resulted in comparable interfaces
with ground enamel, without microscopic signs of micromechanical
retention.
The manufacturers did not include cementation of orthodontic
appliances in the indications for use of self-adhesive cements. Nevertheless,
the shear bond strength of orthodontic brackets cemented to unground enamel
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with RelyX Unicem (Vicente et al. 2005; Bishara et al. 2006b) and Maxcem
(Bishara et al. 2006a) was assessed in order to evaluate the potential benefits
of self-adhesive cements in orthodontic clinical procedures. Both cements
revealed significantly lower bond strengths in comparison to conventional
orthodontic resin adhesive systems that utilize phosphoric acid etching of the
enamel surface (Vicente et al. 2005; Bishara et al. 2006a; Bishara et al.
2006b). However, the lower bond strength of orthodontic brackets cemented
to enamel by RelyX Unicem was thought to be clinically acceptable (Vicente
et al. 2005).
Dentin
The adhesion of RelyX Unicem (De Munck et al. 2004; Abo-Hamar et al.
2005; Walter et al. 2005; Escribano and de la Macorra 2006; Goracci et al.
2006; Yang et al. 2006; Al-Assaf et al. 2007; Hikita et al. 2007;
Piwowarczyk et al. 2007) and Maxcem (Goracci et al. 2006) to coronal
dentin was evaluated by bond strength (De Munck et al. 2004; Abo-Hamar et
al. 2005; Walter et al. 2005; Goracci et al. 2006; Yang et al. 2006; Al-Assaf
et al. 2007; Hikita et al. 2007; Piwowarczyk et al. 2007) and morphological
investigations (De Munck et al. 2004; Goracci et al. 2006; Yang et al. 2006;
Al-Assaf et al. 2007). The retentive strength of zirconia crowns cemented
with RelyX Unicem was also assessed (Ernst et al. 2005; Palacios et al.
2006). In the majority of the studies self-adhesive cements were light-cured
(De Munck et al. 2004; Walter et al. 2005; Escribano and de la Macorra
2006; Goracci et al. 2006; Palacios et al. 2006; Hikita et al. 2007) while in
two studies materials were left to autopolymerize (Yoshida et al. 2004; Al-
Assaf et al. 2007). The effect of curing mode to shear bond strength to dentin
of dual-cured resin cements, including RelyX Unicem, was assessed in two
studies (Abo-Hamar et al. 2005; Piwowarczyk et al. 2007). Light curing
99
resulted in higher bond strengths and therefore it was recommended for
clinical procedures (Abo-Hamar et al. 2005; Piwowarczyk et al. 2007).
Bond strength studies were conducted using shear (Abo-Hamar et al. 2005;
Piwowarczyk et al. 2007) tensile(Al-Assaf et al. 2007) and microtensile bond
strength test (De Munck et al. 2004; Walter et al. 2005; Escribano and de la
Macorra 2006; Goracci et al. 2006; Yang et al. 2006; Hikita et al. 2007), and
the recorded bond strength values vary greatly depending on the applied test
methodology. Nevertheless, the majority of the results obtained is consistent
and demonstrate that in contrast to enamel adhesion, RelyX Unicem performs
comparably to other multi-step systems on coronal dentin. Its bond strengths
were often compared to Panavia F, and no significant differences (De Munck
et al. 2004; Abo-Hamar et al. 2005; Goracci et al. 2006; Al-Assaf et al. 2007;
Hikita et al. 2007; Piwowarczyk et al. 2007) or higher bond strength of
RelyX Unicem were reported (Walter et al. 2005). In comparison to resin
cements that utilize etch-and-rinse adhesive systems RelyX Unicem bonded
equally effectively when compared to Variolink II (Ivoclar Vivadent) (Abo-
Hamar et al. 2005; Hikita et al. 2007), Nexus 2 (Kerr) (Hikita et al. 2007),
RelyX ARC (3M ESPE) and Calibra (Dentsply Caulk) (Piwowarczyk et al.
2007). Unlike previous findings, significantly lower microtensile bond
strength of RelyX Unicem to dentin compared to Panavia F 2.0 (Escribano
and de la Macorra 2006; Yang et al. 2006), Multilink (Escribano and de la
Macorra 2006) and Variolink II (Piwowarczyk et al. 2007) was also reported.
In contrast to the positive effect observed on enamel, acid etching was
detrimental to RelyX Unicem dentin adhesion (De Munck et al. 2004; Hikita
et al. 2007). Its microtensile bond strength following acid etching was
significantly lower compared to the one obtained when the cement was used
without any treatment of the dentin surface (De Munck et al. 2004; Hikita et
al. 2007). This was attributed to the self-adhesive cements inability to
100
infiltrate the collagen depleted by the etching step (De Munck et al. 2004).
Although higher seating force had no effect on enamel adhesion, it improved
microtensile bond strengths of RelyX Unicem and Panavia F 2.0 to dentin
(Goracci et al. 2006). Conversely, the microtensile bond strength of Maxcem
to dentin was significantly lower compared to RelyX Unicem, and was not
influenced by the heavier seating pressure (Goracci et al. 2006).
The application of RelyX Unicem (De Munck et al. 2004; Goracci et
al. 2006; Yang et al. 2006; Al-Assaf et al. 2007) and Maxcem (Goracci et al.
2006) to coronal dentin does not result in the formation of a hybrid layer and
resin tags. The morphological findings at the cement-dentin interface formed
by self-adhesive cements were noticeably different in comparison to the
interface formed with resin cements that require pretreatment of the dentin
surface (De Munck et al. 2004; Goracci et al. 2006; Yang et al. 2006; Al-
Assaf et al. 2007).
Zirconium oxide crowns and fixed partial dentures may be cemented
using conventional non-bonding cements due to their high fracture resistance.
However, these restorations may also benefit from adhesive cementation
(Blatz et al. 2003). Retention of zirconia crowns cemented with RelyX
Unicem was investigated in two studies (Ernst et al. 2005; Palacios et al.
2006). The retentive strength of Lava crowns (3M ESPE) cemented with the
self-adhesive cement was not significantly different in comparison to the
other multi-step resin luting agents tested (Ernst et al. 2005). Likewise,
comparable retentive strengths of Procera AllZirkon copings (Nobel Biocare)
were found between RelyX Unicem, Panavia F and a resin modified glass
ionomer cement (RelyX Luting, 3M ESPE) (Palacios et al. 2006).
101
Root dentin
Since root dentin is different in nature from coronal dentine and variations in
its structure may affect bonding, the adhesion to this substrate is usually
assessed separately (Ferrari et al. 2000; Mjor et al. 2001). The adhesion of
RelyX Unicem to root dentin was investigated in light-cure mode when this
cement was used for the cementation of fiber posts (Bateman et al. 2005;
Goracci et al. 2005; Bitter et al. 2006a; Sadek et al. 2006) and titanium
dowels (Balbosh et al. 2005). In order to evaluate the effectiveness of
cementation, thin-slice push out tests (Goracci et al. 2005; Bitter et al. 2006a;
Sadek et al. 2006), retention tests (Balbosh et al. 2005; Bateman et al. 2005)
and morphological evaluations of the cement-root dentin interface (Goracci
et al. 2005) were performed.
Similarly to bond strengths on coronal dentin, the push-out strength of
RelyX Unicem was comparable to Panavia F 2.0. However, both cements
resulted in significantly lower push-out strengths compared to Variolink II
cement in combination with an etch-and-rinse dual cured adhesive Excite
DSC (Ivoclar Vivadent) (Goracci et al. 2005). Different results were reported
in another investigation, where RelyX Unicem push-out strength was
significantly higher than the push-out strengths of Panavia F, Variolink II and
other resin cements investigated (Bitter et al. 2006a). Moreover, its push-out
strength was significantly higher after thermocycling. The authors speculated
that the self-adhesive cements moisture tolerance, purported by the
manufacturer, may partly explain its favorable adhesion in the root canals
(Bitter et al. 2006a). A significant increase in RelyX Unicem push-out
strength was found after 24 hours of water storage in comparison to
immediate testing (Sadek et al. 2006).
Retention of quartz fiber posts cemented with RelyX Unicem was
comparable to the retention obtained with the conventional resin cement
102
RelyX ARC in combination with an etch-and-rinse adhesive (Bateman et al.
2005). When RelyX Unicem was used for titanium dowel cementation it
performed comparably to a zinc phosphate, glass ionomer and a resin cement
(Panavia 21) (Balbosh et al. 2005).
Similarly to coronal dentin, no hybrid layer and inability to etch
through the smear layer formed in the root canal were observed when RelyX
Unicem (Goracci et al. 2005) was used for adhesive cementation of fiber
posts.
Adhesion to restorative materials
Endodontic posts
Only one study assessed the adhesion of RelyX Unicem to endodontic posts,
using the thin-slice push out test after the tribochemically coated (CoJet, 3M
ESPE) zirconia (CosmoPost, Ivoclar Vivadent) and fiber posts (FRC Postec,
Ivoclar Vivadent) were cemented in artificial post spaces (Bitter et al.
2006b). The push-out strength of RelyX Unicem was significantly higher to
fiber posts than to zirconia posts. On both substrates it performed comparably
to the cements that resulted in the highest push-out strengths (Bitter et al.
2006b).
Ceramics
Several studies investigated shear (Piwowarczyk et al. 2004; Kumbuloglu et
al. 2005; Piwowarczyk et al. 2005b; Reich et al. 2005; Kumbuloglu et al.
2006; Luthy et al. 2006) and microtensile (Pisani-Proenca et al. 2006) bond
strength of RelyX Unicem to different types of ceramic: high-strength
cylindrical aluminum oxide (Piwowarczyk et al. 2004), leucite-reinforced
(Piwowarczyk et al. 2004), lithium disilicate (Piwowarczyk et al. 2004;
103
Kumbuloglu et al. 2005; Pisani-Proenca et al. 2006), machinable feldspatic
(Reich et al. 2005) and zirconia ceramics (Piwowarczyk et al. 2005b;
Kumbuloglu et al. 2006; Luthy et al. 2006). The bond strength values varied
in different studies, depending on the ceramic treatment and the aging
conditions. However, the obtained results are in agreement, demonstrating
that this cement achieves bond strength that is either higher or comparable to
other investigated materials. In the majority of the studies, RelyX Unicem
was light cured (Kumbuloglu et al. 2005; Reich et al. 2005; Kumbuloglu et
al. 2006; Luthy et al. 2006; Pisani-Proenca et al. 2006). Two studies
investigated the influence of the curing mode on bond strength of dual-curing
resin cements to high-strength cylindrical aluminum oxide, leucite-
reinforced, lithium disilicate (Piwowarczyk et al. 2004) and zirconia
ceramics (Piwowarczyk et al. 2005b). It was reported that light
polymerization of the investigated dual-curing resin cements, including
RelyX Unicem, significantly increased bond strengths in comparison to
autopolymerization.
In comparison with 10 cements from different classes, only RelyX
Unicem resulted in high shear bond strengths after 14 days of water storage
and thermocycling to all the investigated substrates: high-strength cylindrical
aluminum oxide ceramic (following sandblasting), leucite-reinforced and
lithium disilicate ceramic (following etching with hydrofluoric acid and
silanization). Interestingly, water storage and thermocycling increased the
bond strength of all resin cements and the self-adhesive universal resin
cement (Piwowarczyk et al. 2004). In a study by Kumbuloglu et al, RelyX
Unicem revealed lower shear bond strengths to lithium disilicate ceramics
than the other resin cements investigated (Kumbuloglu et al. 2005).
However, in this study no pretreatment of the ceramic surface was
performed, in contrast to the previous study in which the ceramic surface was
104
etched and silanized (Piwowarczyk et al. 2004). following the manufacturer’s
directions (3M ESPE product profile, RelyX Unicem). Microtensile bond
strengths of RelyX Unicem, Multilink and Panavia F increased when lithium
disilicate ceramics (IPS Empress 2) was etched and silanized, in comparison
to bond strengths to untreated ceramic surfaces (Pisani-Proenca et al. 2006).
RelyX Unicem microtensile bond strength was comparable to Multilink
following etching and silanization, and higher in comparison to Panavia F,
regardless of the ceramic surface treatment (Pisani-Proenca et al. 2006). High
bond strengths that were increased after thermocycling were also reported to
etched and silanized machinable feldspatic ceramic (Reich et al. 2005). This
study reported that etching with hydrofluoric acid and silanization was the
most beneficial treatment to gain a reliable bond strength to the majority of
materials investigated, including RelyX Unicem (Reich et al. 2005).
RelyX Unicem shear bond strength to sandblasted (110 �m aluminum
oxide) or tribochemically coated (Rocatec, 3M ESPE) zirconia ceramics
(Lava, 3M ESPE) was investigated and compared with 10 luting cements
from different material classes (Piwowarczyk et al. 2005b). Similarly to the
previous study using the same materials and methodology for different
ceramic substrates (Piwowarczyk et al. 2004), the shear bond strength of this
cement increased after 14 days of water storage and thermocycling. It was
also the highest in comparison with other investigated materials regardless of
the ceramic surface treatment (Piwowarczyk et al. 2005b). High shear bond
strengths, comparable to Panavia F, were also reported to zirconia ceramics
with and without previous tribochemical treatment of the ceramic surface
(Rocatec) and regardless of the aging condition (Kumbuloglu et al. 2006;
Luthy et al. 2006).
105
Titanium abutments
Retention forces of noble alloy castings cemented on titanium abutments with
different cements were investigated (Wolfart et al. 2006). The retention
achieved using RelyX Unicem was comparable to retention achieved using
polycarboxylate cement, and significantly higher in comparison to retention
following the cementation with zinc oxide, zinc phosphate and glass ionomer
cements (Wolfart et al. 2006).
Marginal adaptation
In vitro marginal adaptation of RelyX Unicem (Behr et al. 2004; Rosentritt
et al. 2004; Frankenberger et al. 2008) and Maxcem (Frankenberger et al.
2008) was evaluated following the cementation of all-ceramic MOD inlay
restorations (IPS Empress, Ivoclar Vivadent) (Rosentritt et al. 2004;
Frankenberger et al. 2008) and all-ceramic crowns (IPS Empress 2, Ivoclar
Vivadent) (Behr et al. 2004). Marginal adaptation of all-ceramic MOD inlays
was assessed in enamel and in dentin. These authors reported over 90% of
perfect margin in RelyX Unicem specimens, which was comparable to resin
cements Variolink and Panavia F both before and after thermocycling and
mechanical loading. Marginal integrity deteriorated after loading for all the
cements investigated, but significantly lower percentage of perfect margin
was recorded only for Variolink in dentin, at both tooth-cement and cement-
inlay interface (Rosentritt et al. 2004). Another investigation reported that
RelyX Unicem offers a tight seal at dentin margins, while Maxcem resulted
in a significantly lower percentage of perfect margin (Frankenberger et al.
2008). However, it was ponted out that self-adhesive cements cannot
compete with cements which utilize etch-and-rinse adhesives in terms of
enamel bonding performance (Frankenberger et al. 2008).
106
Marginal adaptation of RelyX Unicem used for the cementation of all
ceramic crowns was assessed in dentin, before and after thermal and
mechanical loading that was applied with the intention to simulate a five-year
period of intraoral stress. Over 90% of perfect margin was observed in RelyX
Unicem specimens. Its adaptation was not influenced either by previous
application of Prompt-L-Pop adhesive or by loading, and was comparable to
Variolink resin cement (Behr et al. 2004).
Microleakage
Microleakage of RelyX Unicem was evaluated subsequently to cementation
of porcelain veneers (Ibarra et al. 2007), all-ceramic inlay restorations
(Rosentritt et al. 2004; Fabianelli et al. 2005), all-ceramic crowns (Behr et al.
2004), gold inlays (Fabianelli et al. 2005) and full cast crowns (Piwowarczyk
et al. 2005a). Porcelain veneers enamel microleakage was significantly
higher when the self-adhesive cement was used in comparison to resin
cement Variolink combined with the etch-and-rinse adhesive Excite (Ivoclar
Vivadent). However, in accordance with bond strength data (De Munck et al.
2004; Hikita et al. 2007) enamel microleakage decreased to values
comparable to Variolink if RelyX Unicem was used with the etch-and-rinse
adhesive (Single Bond, 3M ESPE) or a strong self-etch adhesive (Adper
Prompt-L-Pop, 3M ESPE) (Ibarra et al. 2007). Conversely, the application of
these adhesives on dentin had an unfavorable effect on microleakage, while
the self-adhesive cement used without any dentin pretreatment resulted in
microleakage values comparable to Variolink (Ibarra et al. 2007). When the
self-adhesive cement was used for the cementation of all-ceramic MOD
inlays, microleakage in enamel and dentin was comparable to resin cements
Variolink (Rosentritt et al. 2004; Fabianelli et al. 2005) and Panavia F
107
(Rosentritt et al. 2004). Microleakage of this cement following the
cementation of all-ceramic crowns was investigated in dentin, and was
significantly lower compared to Variolink (Behr et al. 2004).
In a microleakage investigation of various cementing agents for full
cast crowns, RelyX Unicem revealed the lowest microleakage both in enamel
and in dentin (Piwowarczyk et al. 2005a). Enamel microleakage was
significantly lower compared to RelyX ARC resin cement used with the etch-
and-rinse adhesive Single Bond and the zinc phosphate cement, and
comparable to glass ionomer cements and the self-etching cement Panavia F
(Piwowarczyk et al. 2005a). The authors speculated that the specific
multifunctional phosphoric-acid methacrylates that this cement contains are
able to react with the tooth surface in multiple ways, resulting in an effective
seal. Apart from the formation of complex compounds with calcium ions,
different kinds of physical interactions like hydrogen bonding or dipole-to-
dipole interactions were assumed to favorably influence self-adhesion
(Piwowarczyk et al. 2005a). In another microleakage investigation, RelyX
Unicem performed significantly better than the zinc phosphate cement with
gold inlays (Fabianelli et al. 2005).
Mechanical properties
Mechanical properties of RelyX Unicem cement were assessed by surface
microhardness (Kumbuloglu et al. 2004), degree of conversion (Kumbuloglu
et al. 2004), compressive strength (Piwowarczyk and Lauer 2003;
Kumbuloglu et al. 2004) and flexural strength (Piwowarczyk and Lauer
2003) investigations. Fatigue (Baldissara et al. 2006; Uy et al. 2006) and
fracture resistance (Komine et al. 2004; Burke et al. 2006) of teeth restored
using RelyX Unicem were also evaluated.
108
After 1 week of water storage, RelyX Unicem in light-cure mode had
the highest values of hardness and compressive strength when it was
compared with three other resin cements (RelyX ARC, Panavia F and
Variolink). However, in the same study it was reported that its degree of
conversion was the lowest: 56% when the cement was light cured and only
26% when it was autopolymerized (Kumbuloglu et al. 2004). In another
study, the same three resin cements had the highest flexural and compressive
strengths, followed by RelyX Unicem, while all four materials were
statistically stronger than resin-modified glass ionomer cements, glass
ionomer cements and zinc phosphate cements (Piwowarczyk and Lauer
2003). This study also assessed the influence of curing mode on flexural and
compressive strengths of dual-curing resin cements. No significant
differences between the properties of light-cured and autopolymerized
cements were found (Piwowarczyk and Lauer 2003).
Fatigue resistance of sandblasted (110 �m aluminum oxide) glass-
infiltrated alumina ceramic (In Ceram Alumina, Vita) bonded to dentin was
lower when RelyX Unicem was used in comparison to Panavia F (Baldissara
et al. 2006). Both cements were used in the self-cure mode (Baldissara et al.
2006). In the assessment of load-fatigue performance of gold crowns luted
with resin cements, RelyX Unicem survived lower number of cycles
compared to C & B Opaque (Bisco Inc., Schaumburg, IL, USA) and Calibra
Esthetic resin cement (Dentsply Caulk) but behaved comparably to Panavia F
and zinc phosphate cement (Uy et al. 2006). The marginal areas in teeth
where the crowns were luted with resin cements were light polymerized (Uy
et al. 2006). Fracture resistance of teeth restored with all ceramic crowns
luted with RelyX Unicem in light-cure (Burke et al. 2006b) and self-cure
(Komine et al. 2004) mode was comparable to fracture resistance of teeth
restored using a conventional resin cement Mirage ABS/FLC (Mirage Dental
109
Systems, Kansas City, KS, USA) (Burke et al. 2006b) and Super-Bond C&B
(Sun Medical, Shiga, Japan) (Komine et al. 2004).
Biocompatibility
In a study by de Souza Costa et al. pulpal response to RelyX Unicem and
Variolink II used to bond inlay restorations was investigated and compared
(de Souza Costa et al. 2006). Although slight tissue disorganization was
observed in the RelyX Unicem samples at the 7-day period, no pulpal
response was present in most of the samples evaluated at 60 days.
Conversely, Variolink II associated with the adhesive system Excite
demonstrated more aggressive effects to the pulp–dentin complex. A
discrete-to-moderate initial pulpal inflammatory response was observed that
persisted until the 60-day period. The authors speculated that RelyX Unicem
benefited from its chemical adhesion to tooth structure, low solubility and a
self-neutralizing mechanism during the setting reaction. These manufacturer-
declared properties were assumed to prevent hydrolysis and diffusion of
cement’s components across dentinal tubules. The mild inflammatory
reaction that was observed at the 7-day period was explained by the initially
low pH of the cement (de Souza Costa et al. 2006).
Chemical adhesion and fluoride release
Until recently, chemical adhesion to hydroxyapatite was proven for glass
ionomer cements (Wilson et al. 1983; Yoshida et al. 2000) and 10-MDP (10-
methacryloxydecyl dihydrogen phosphate) and 4-MET (4-methacryloxyethyl
trimellitic acid) functional monomers used in some self-etching adhesive
systems (Yoshida et al. 2004). In a study by Gerth et al (Gerth et al. 2006)
110
the potential for chemical interaction between RelyX Unicem and
hydroxyapatite was investigated and compared to resin cement Bifix (Voco,
Cuxhaven, Germany) in combination with an etch-and-rinse adhesive system.
It was reported that RelyX Unicem showed high chemical interaction with Ca
ions derived from hydroxyapatite, which was enhanced in comparison to
Bifix (Gerth et al. 2006).
The same authors investigated the exact composition of RelyX
Unicem and Bifix and detected a fluoride content of 10% with RelyX
Unicem and 2% with Bifix. Although fluoride release from restorative
materials depends on their fluoride content, this process is also influenced by
several other factors (Wiegand et al. 2007). More importantly, a direct
relationship between fluoride release from restorative materials and its actual
anticariogenic effects has not been determined in vivo (Burke et al. 2006).
Therefore, the clinical significance of fluoride release from self-adhesive
cements in terms of their cariostatic properties remains to be determined.
Ratings in clinical use
No clinical studies that investigated self-adhesive cements have been
published yet. However, some information on the handling properties of
these materials is available. Product Research and Evaluation by Practitioners
(PREP) Panel, a United Kingdom-based group conducted a practice-based
evaluation of RelyX Unicem handling. The authors reported that this cement
achieved ratings for ease of use that were superior to the pre-study resin-
based and conventional luting materials in the practices of 13 United
Kingdom dental practitioners (Burke et al. 2006a).
111
Conclusions
Based on the literature in vitro data, adhesion of the most investigated self-
adhesive cement to dentin and various restorative materials is satisfactory and
comparable to other multi-step resin cements. An interesting and clinically
relevant concept is the possibility for dentin bond strength enhancement by
the application of higher seating pressure. Light curing provided higher bond
strengths than autopolymerization to dentin and to various types of ceramic
materials. Some investigations have reported that artificial aging resulted in
increased push-out strength to root dentin and increased bond strengths to
various fixed prosthodontic restorative materials. Adhesion to enamel
appears to be a weak link in bonding properties of self-adhesive cements.
Although it may benefit from previous acid etching, this procedure is
detrimental to dentin adhesion. Therefore, its potential employment would
require an extreme precision in applying the acid solely on enamel, which is
difficult to achieve in clinical conditions. Chemical adhesion and fluoride
release may play a role in durability and cariostatic properties of these
materials, which remains to be determined in vivo.
Self-adhesive cements appear to offer a promising new approach in
indirect restorative procedures. However, the available literature data is based
on studies that investigated only one of the cements that are currently
available to clinicians. More importantly, long term clinical performance of
these materials needs to be assessed prior to making a general
recommendation for their use.
112
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3.2. Evaluation of the adhesion of fiber posts cemented using different
adhesive approaches
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European Journal of Oral Sciences 2008; 116(6): 557-563.
Introduction
Reconstructing endodontically treated teeth with fiber post and core systems
has been widely investigated (Schwartz and Robbins 2004; Schwartz and
Fransman 2005). This treatment option may offer advantages over
conventional cast posts or prefabricated metallic posts (Martinez-Insua et al.
1998; Sirimai et al. 1999; Cormier et al. 2001; Akkayan and Gulmez 2002;
Newman et al. 2003; Fokkinga et al. 2004; Hayashi et al. 2006).
Notwithstanding the satisfactory clinical performance of fiber post and core
systems (Cagidiaco et al. 2008), debonding of the post was observed as the
main failure mode (Ferrari et al. 2000; Mannocci et al. 2002; Monticelli et al.
2003; Cagidiaco et al. 2007; Ferrari et al. 2007a).
The success of fiber post and core restorative procedure depends in
part on the cementation technique used to create a link between the post and
root canal dentin. Contemporary resin cements may be divided into three
subgroups according to the adhesive approach used to prepare the tooth prior
to cementation. The first group utilizes etch-and-rinse adhesive systems. In
the second group, enamel and dentin are prepared using self-etching primers.
The third and the most recently introduced group of resin cements is
represented by self-adhesive cements.
In the majority of clinical investigations fiber posts were cemented
using etch-and-rinse adhesives in combination with self-cured (Ferrari et al.
2000a; Ferrari et al. 2000b; Malferrari et al. 2003; Mannocci et al. 2005;
119
Ferrari et al. 2007a) and dual-cured resin cements (Ferrari et al. 2000b;
Monticelli et al. 2003; Grandini et al. 2005; Naumann et al. 2005a; Naumann
et al. 2005b; Cagidiaco et al. 2007; Ferrari et al. 2007b). It was reported that
the level of operator’s experience does not influence retention of fiber posts
cemented using etch-and-rinse adhesive in laboratory conditions (Simonetti
et al. 2006). Nevertheless, scientists and manufacturers have been
continuously challenged by a general trend to simplify the clinical
procedures. The simpler, self-etching adhesive approach, offers the shorter
adhesive application time and reduced number of clinical steps. It is
considered to be less technique sensitive as the clinical assessment of optimal
dentin wetness after rinsing the phosphoric acid is avoided (Van Meerbeek et
al. 2003). However, the most simple, one-step self-etching adhesives, are
also associated with permeability and phase separation which may affect
bond durability (Van Meerbeek et al. 2005).
The adhesion of fiber posts luted using self-etching adhesives has
been assessed only in laboratory studies, most commonly by comparing them
with the performance of etch-and-rinse adhesives. The findings on self-
etching adhesives performance in fiber post cementation are not consistent. It
was reported that microleakage at the cement/root dentin interface was
significantly higher when self-etching primer was used for fiber post
cementation, in comparison to etch-and-rinse adhesive (Mannocci et al.
2001a). Likewise, resin-root dentin interdiffusion zone was less pronounced
following self-etching approach than with etch-and-rinse adhesive approach
(Mannocci et al. 1999). On the other side, no differences between self-
etching and etch-and-rinse approach were found when representative
materials were investigated using microtensile bond strength test (Mannocci
et al. 2001b) and push-out strength test (Kurtz et al. 2003; Akgungor and
Akkayan 2006).
120
Self-adhesive cements represent the least investigated group of resin
cements. Their in vitro performance in fiber post cementation was
investigated using push-out strength test (Goracci et al. 2005; Bitter et al.
2006; de Durao Mauricio et al. 2007; Huber et al. 2007; Wang et al. 2008),
and the results are contradictory. In comparison with etch-and-rinse
approach, both lower (Goracci et al. 2005; de Durao Mauricio et al. 2007;
Wang et al. 2008) and higher (Bitter et al. 2006) push-out strength of self-
adhesive cement was reported. In comparison to self-etching approach,
inferior (de Durao Mauricio et al. 2007), comparable (Goracci et al. 2005)
and superior (Huber et al. 2007) behaviour of the self-adhesive approach was
reported, even though the same self-adhesive cement was investigated in all
the studies. In the only clinical study available, no failures were recorded
after 2-year follow-up of restorations retained by fiber posts cemented with
self-adhesive cement (Naumann et al. 2007).
Self-etching and self-adhesive approach offer simplicity and chair-
time reduction, which may be beneficial in the clinical setting. However, the
information on the most favourable fiber post cementation technique is
lacking in the present literature. Therefore, the aim of the study was to
investigate the adhesion of fiber posts cemented to intraradicular dentin with
luting agents that utilize three currently available adhesive approaches: etch-
and-rinse, self-etch and self-adhesive. The working hypothesis was that the
simpler, self-etching and self-adhesive approaches are equally effective as the
clinically proven etch-and-rinse approach. The null hypothesis tested is that
there are no differences in the retention of fiber posts cemented with different
luting agents.
121
Material and methods
Specimens preparation
Forty two intact human premolars with a single root canal, extracted due to
orthodontic reasons were selected for the study. The teeth were hand-scaled
and stored in 1% chloramine T at 4°C for no more than six months until use.
The crown of each tooth was removed at 1mm above the cementoenamel
junction, using a slow speed diamond saw (Isomet, Buehler, Lake Bluff, IL,
USA) under copious water-cooling. The roots were endodontically
instrumented at a working length of 1 mm from the apex to a #35 master
apical file (Maillefer), Gates-Glidden drills #2 to #4 (Maillefer), and 2.5%
sodium hypochlorite irrigation. For canal obturation, thermoplasticized,
injectable gutta-percha (Obtura, Texceed Corp, Costa Mesa, CA, USA) and a
resin sealer (AH Plus Jet, Dentsply DeTrey, Konstanz, Germany) were
employed. Teeth were randomly divided into six groups. In each group,
different resin cement with its adhesive system (if needed) and fiber post was
used. The groups were classified according to the adhesive approach into
three categories: etch-and rinse, self-etch and self-adhesive.
Etch-and-rinse groups:
� Calibra resin cement, XPBond adhesive/Self curing activator, RadiX
Fiber Post (Dentsply Caulk, Milford, DE, USA).
� FluoroCore 2 core build-up material, XPBond adhesive/Self curing
activator, RadiX Fiber Post (Dentsply Caulk)
� MultiCore Flow luting/core build-up material, Excite DSC adhesive,
FRC Postec Plus fiber post (Ivoclar Vivadent, Schaan, Liechtenstein)
122
Self-etch group:
� Panavia F 2.0, ED primer (Kuraray, Osaka, Japan), RadiX Fiber Post
(Dentsply Caulk)
Self-adhesive groups:
� Experimental self-adhesive cement, RadiX Fiber Post (Dentsply
Caulk)
� RelyX Unicem, RelyX Fiber Post (3M ESPE, Seefeld, Germany)
In each root-treated tooth, a 9 mm deep post space was prepared with low-
speed drills provided by the post manufacturer. The materials were strictly
handled according to the manufacturer’s instructions. The application mode
of all materials used in each group, their composition and their batch
numbers are reported in Table 1 and 2 respectively.
123
Table 1: Application mode of the materials used in the study
Luting agent (manufacturer)
Fiber post treatment
Post space dentin treatment Cementation
Calibra (Dentsply Caulk)
Clean RadiX Fiber Post with alcohol; air dry; treat surface with Calibra Silane; air dry
Apply Caulk 34% Tooth Conditioner Gel to the post space through a needle; rinse off after 15 seconds with water using an endodontic syringe; remove excess water with a gentle air blast; use paper points to remove residual moisture without desiccating the etched dentin surfaceMix XPBond adhesive with Self-Cure Activator (1:1); apply mixture to the post space with a microbrush for 20 seconds; gently air dry and then remove excess with paper points.
Mix Calibra cement components 1:1; spread mixed cement on surface of post and into the post preparation with a lentulo spiral; seat the post immediately; light cure for 40 seconds
FluoroCore 2 (Dentsply Caulk)
Clean RadiX Fiber Post with alcohol; air dry
Mix FluoroCore 2 base and catalyst 1:1 for 30 seconds; apply the material on the post and seat the post immediately; allow the material to self-cure for 7 minutes, then light cure for 40 seconds
MultiCore Flow (Ivoclar Vivadent)
Clean FRC Postec Plus post with phosphoric acid gel (Total Etch) for 60 seconds, rinse and dry. Apply Monobond S and dry after 60 seconds.
Apply Total Etch to the post space through a needle; rinse off after 15 seconds with water using an endodontic syringe; remove excess water with a gentle air blast; use paper points to remove residual moisture without desiccating the etched dentin surface. Apply activated Excite DSC adhesive to the post space with a proprietary microbrush for 10 seconds; gently air dry and then remove excess with paper points.
Mix the components of MultiCore Flow and apply the mixed material to the post; seat the post into the root canal and hold it in place using slight pressure; light cure for 60 seconds.
124
Table 1 (continued): Application mode of the materials used in the study
Luting agent (manufacturer)
Fiber post treatment
Post space dentin treatment Cementation
Panavia F 2.0 (Kuraray)
Clean RadiX Fiber Post with alcohol; air dry
Mix ED primer II (Liquid A and Liquid B 1:1); apply mixture to the post space with a microbrush for 30 seconds; gently air dry and then remove excess with paper points.
Mix Panavia F 2.0 paste A and paste B for 20 seconds; apply the mixed paste to the post and seat it in place; light cure for 40 seconds.
Experimental self-adhesive (Dentsply Caulk)
No treatment
Apply experimental cement directly to the post space through an endodontic application tip that is attached to the double syringe; place the post; allow the cement to self-cure for 5 min, then light cure for 40 seconds.
RelyX Unicem (3M ESPE)
Clean RelyX Fiber Post with alcohol, air dry
Mix the capsule; apply RelyX Unicem cement directly to the post space through a disposable application tip that is attached to the capsule; place the post; leave the cement to self- cure for 5 min and then light cure for 40 seconds.
125
Table 2: Composition and batch numbers of the materials used in the study Material (manufacturer)
Composition Batch number
Caulk 34% Tooth Conditioner Gel (Dentsply Caulk)
34% phosphoric acid 0704001801
XPBond adhesive (Dentsply Caulk)
carboxylic acid modified dimethacrylate (TCB resin), phosphoric acid modified acrylate resin (PENTA), urethane dimethacrylate (UDMA), triethyleneglycol dimethacrylate (TEGDMA), 2-hydroxyethylmethacrylate (HEMA), Butylated benzenediol (stabilizer), ethyl-4-dimethylaminobenzoate, camphorquinone, functionalised amorphous silica, tertiary butanol
0702001786
Self-cure activator (Dentsply Caulk)
Urethane Dimethacrylate (UDMA); 2-hydroxyethylmethacrylate (HEMA); Catalyst; Photoinitiators; Stabilizers; Acetone; Water
070119
Calibra Esthetic Resin Cement (Dentsply Caulk)
Base: Dimethacrylate Resins; Camphorquinone (CQ) Photoinitiator; Stabilizers; Glass Fillers; Fumed silica; Titanium Dioxide; Pigments Catalyst: Dimethacrylate Resins; Catalyst; Stabilizers; Glass Fillers; Fumed Silica
070525 0705291
Calibra Silane Coupling Agent (Dentsply Caulk)
Acetone; Ethyl Alcohol; Organo Silane 070511
FluoroCore 2 (Dentsply Caulk)
Base: Urethane Dimethacrylate; Di- & Tri-functional Methacrylates; Barium Boron; Catalyst: Fluoroaluminosilicate Glass; Camphorquinone (CQ) Photoinitiator; Photoaccelerators; Silicon Dioxide; Benzoyl Peroxide
0705041
RadiX Fiber Post (Dentsply Caulk)
Zirconium-enriched glass fibers (60%), Epoxy resin matrix (40%)
8626460
Total Etch (Ivoclar Vivadent)
37% phosphoric acid gel J25470
Excite DSC adhesive (Ivoclar Vivadent)
HEMA, dimethacrylates, phosphonic acid acrylate, highly dispersed silicon dioxide, initiators and stabilizers in an alcohol solution. The Excite DSC Brush is coated with initiators.
J23127
MultiCore Flow (Ivoclar Vivadent)
Bis-GMA, urethane dimethacrylate and triethylene glycol dimethacrylate; barium glass, ytterbiumtrifluoride, Ba-Al-fluorosilicate glass and highly dispersed silicon dioxide; catalysts, stabilizers and pigments.
H20666
Monobond S (Ivoclar Vivadent)
1% 3-methacryloxypropyltrimethoxysilane (3-MPS), ethanol/water-based solvent
H34023
FRC Postec Fiber Post (Ivoclar Vivadent)
Glass fibers. Matrix: urethane dimethacrylate, triethylene glycol dimethacrylate. Additional contents: ytterbium trifluoride, highly dispersed silicon dioxide.
K13203
126
Table 2 (continued): Composition and batch numbers of the materials used in
the study
Material (manufacturer)
Composition Batch number
ED primer (Kuraray)
Liquid A: HEMA, 10-methacryloyloxydecyl dihydrogen phosphate (MDP), N-methacryloyl 5-aminosalicylic acid (5-NMSA), dimethacrylate, sodium aromatic sulphinate, water, accelerator Liquid B: 5-NMSA, accelerator, water, sodium benzene sulphinate
00238B 00116B
Panavia F 2.0 (Kuraray)
Base: Hydrophobic aromatic and aliphatic dimethacrylate, sodium aromatic sulphinate, N,N-diethanol-p-toluidine, functionalized sodium fluoride, silanized barium glass sodium benzene sulphinate Catalyst: MDP, hydrophobic aromatic and aliphatic dimethacrylate, photoinitiator, dibenzoyl peroxide, hydrophilic dimethacrylate, silanized silica
00249A 00058D
Experimental self-adhesive cement (Dentsply Caulk)
Information not available HL6-91-1T
RelyX Fiber Post (3M ESPE)
glass fibers (60 - 70% by weight) embedded in epoxy-resin matrix containing zirconia filler
050230703
RelyX Unicem cement (3M ESPE)
Powder: glass fillers, silica, calcium hydroxide, self-curing initiators, pigments, light-curing initiators, substituted pyrimidine, peroxy compound Liquid: methacrylated phosphoric esters, dimethacrylates, acetate, stabilizers, self-curing initiators, light-curing initiators
288418
127
Following the placement of fiber post, the excess of luting agent was
removed prior to light curing. Light-curing was performed through the post
using a conventional quartz–tungsten–halogen light (600 mW/cm2 output;
VIP; Bisco, Schaumburg, IL, USA). The exposed dentin along the coronary
part of the root and the coronal part of luting agent/fiber post were
completely covered with glass ionomer cement (Fuji II, GC corp., Tokyo,
Japan). After storage in water for 24 h at 37°C (ISO/TS 11405:2003), the
roots were processed for the evaluation of push-out strength.
Push-out strength evaluation
In order to assess the adhesion of fiber posts, thin-slice push-out test was
used (Goracci et al. 2004). The portion of each root that contained the
bonded fiber post was sectioned into five to six 1 mm-thick serial slices with
the Isomet saw under water cooling (Figure 1). Seven bonded roots from
each group resulted in 35-42 slices per group for push-out strength
evaluation. None of the slices failed during sectioning process and all
fabricated slices were used for the evaluation of push-out strength. The
number of slices in each experimental group of at least 35 was determined
from a preliminary power analysis that was conducted in order to assure the
power of at least 90% for finding the statistically significant differences
given the standard value of type I errors (0.05) and assuming the difference
of 4 MPa as relevant for this investigation. The within group standard
deviation that was used in the calculations was assumed to be 4 MPa, based
on the previous investigations of push-out strength (Sadek et al. 2006). The
sample size and power calculations were handled by SigmaStat (Systat
Software Inc, San Jose, California, USA).
128
Figure 1: Schematic drawing of the specimen preparation for push-out
strength testing. Each root was sectioned into 1 mm-thick slices. The apical
surface of each root slice was marked (M) in order to assure that the loading
force would be applied in the apical-coronal direction, so as to move the post
toward the larger part of the slice. P: fiber post; C: luting agent; D: root
dentin.
The thickness of each slice was individually measured by a digital calliper,
and then firmly fixed with cyanoacrylate glue to a loading fixture. A
compressive load was applied on the apical aspect of the slice via a universal
testing machine (Controls, Spa, Milano, Italy) that was equipped with a 1
mm-diameter cylindrical plunger.
129
The plunger was positioned so that it only contacted the bonded post
on loading, introducing shear stresses along the bonded interfaces. The
loading force was extended in an apical-coronal direction, so as to move the
post toward the larger part of the root slice. Loading was performed at a
speed of 0.5 mm/min until failure, as manifested by the extrusion of the post
segment from the root slice. This was further confirmed by the appearance of
a sharp drop along the load/time curve recorded by the testing machine. The
push-out strength (MPa) was computed by dividing the load at debonding
(Newtons) by the area (A) of the bonded interface. The latter was calculated
through the formula: A=��R+r)[(h2 + (R-r)2]0.5 where R represents the
coronal post radius, r represents the apical post radius and h is the thickness
of the slice in mm. The diameters of the post and the thickness of the slice
were individually measured using a digital calliper with 0.01 mm accuracy.
The failure mode of each debonded specimen after push-out test was assessed
with a stereomicroscope (Nikon SMZ645) at 40x magnification and
classified by the following criteria:
1. Adhesive failure between dentin and luting agent;
2. Adhesive failure between luting agent and post;
3. Cohesive failure within luting agent;
4. Cohesive failure within post;
5. Mixed failure.
One slice representative of each failure mode was processed for scanning
electron microscopy (SEM) evaluation in order to obtain SEM images of the
failure patterns. The slices were rinsed in 96% alcohol solution for 1 minute
and air-dried. Each slice was mounted on a metallic stub, sputter-coated with
gold (Polaron Range SC7620; Quorum Technology), and observed under a
scanning electron microscope (JSM 6060 LV, JEOL).
130
Statistical analysis
Regression analysis was firstly conducted in each group to check if the root
of origin was a significant factor for differences in push-out strengths of root
slices. The regression analysis revealed that in none of the groups the root of
origin was significant. Therefore, the slices were considered as independent
statistical units within each group. The normal distribution of the push-out
strength data was first checked and verified by the Kolmogorov-Smirnov test.
A one-way analysis of variance (ANOVA) was subsequently performed, to
assess the significance of the differences in push-out strength between the
luting agents. As variances were homogeneous (Levene’s test), one-way
ANOVA was followed by the Tukey test for post hoc comparisons. In all the
analyses the level of significance was set at the 0.05 probability level and
calculations were handled by the SPSS 15.0 software (SPSS Inc.; Chicago,
IL, USA).
Results
The type of luting agent significantly influenced the measured push-out
strengths (p<0.001). The results of push-out strength testing are summarized
in Table 3. Multiple comparisons revealed that push-out strengths of Calibra
(etch-and-rinse approach) and RelyX Unicem (self-adhesive approach) were
comparable and significantly higher than push-out strengths of FluoroCore 2
(etch-and-rinse approach) and Panavia F 2.0 (self-etch approach). Push-out
strengths in groups where posts were cemented with MultiCore Flow (etch-
and-rinse approach) and Experimental self-adhesive cement were comparable
to push-out strengths in all the other groups (Table 4). The distribution of
failure modes is reported in Table 3. In the majority of groups the most
frequent type of failure was adhesive between dentin and cement (Figure
131
2A), followed by adhesive failures between post and cement, and mixed
failures (Figure 2B). No cohesive failures within the post were observed in
this study.
Table 3: Push-out strengths and the percentage of slices that failed in the
respective failure mode for each luting agent. Different letters indicate
statistically significant differences (1-way ANOVA and Tukey test, p<0.05).
SD: standard deviation; Med: median value; 25%: lower quartile; 75%: upper
quartile; AD: adhesive failure between dentin and luting agent; AP: adhesive
failure between luting agent and post; CC: cohesive failure within the luting
agent; M: mixed failure.
Adhesive approach
Luting agent
Push-out strength Failure modes [%] Mean (SD)
Med 25% 75% AD AP CC M
Etch-and-rinse
Calibra 12.70
(4.33) A 13.64 10.12 16.39 50 38 0 12
FluoroCore 2
8.07 (4.76) B
7.93 4.70 12.17 49 30 0 21
MultiCore Flow
11.14 (3.88) AB
12.62 8.39 13.88 32 50 0 18
Self-etch Panavia F 2.0
8.68 (5.29) B
8.41 3.67 12.42 47 20 18 15
Self-adhesive
Exp. 10.61
(5.01) AB 9.69 5.40 15.38 56 25 0 19
RelyX Unicem
12.52 (5.47) A
11.33 8.88 15.63 62 5 0 33
132
Table 4: The resultant p values of post-hoc comparisons between the groups
(1-way ANOVA and Tukey test). Significant p values are underlined
(p<0.05)
Calibra FluoroCore
2
MultiCore
Flow
Panavia F
2.0Exp.
RelyX
Unicem
Calibra - 0.001 0.745 0.009 0.491 1.000
FluoroCore 2
0.001 - 0.050 0.994 0.213 0.001
MultiCore Flow
0.745 0.050 - 0.254 0.997 0.820
Panavia F 2.0
0.009 0.994 0.254 - 0.578 0.012
Exp. 0.491 0.213 0.997 0.578 - 0.574
RelyX Unicem
1.000 0.001 0.820 0.012 0.574 -
133
Figure 2: SEM micrographs of failed slices. A: The slice that failed
adhesively between root dentin and luting agent. B: The slice representative
of mixed failure. Remnants of luting agent are visible (asterisk).
134
Discussion Thin-slice push-out strength test is considered to be a valid method to
evaluate fiber post adhesion to root canal walls (Goracci et al. 2007). It was
shown to be more reliable than microtensile technique for measuring the
adhesion of fiber posts (Goracci et al. 2004). Thin-slice push-out strength test
is not difficult to handle, it allows fabrication of several specimens out of one
root, as well as testing for regional differences between root sections
(Goracci et al. 2007). On the other side, the manner in which fiber post in 1
mm-thick root slice is exposed to dislodging forces during push-out testing
cannot be directly compared to functional forces that the post needs to
withstand during clinical service. It is also possible that the sectioning
process may induce artefacts that could influence test results. This may partly
serve as an explanation for the relatively high coefficient of variation in some
groups.
In each group, resin cement/adhesive was used with the manufacturer
recommended fiber post. The only exception was made in case of Panavia F
2.0, as no specific fiber post is recommended by the manufacturer (Kuraray).
This experimental set-up has limitations, as it was previously reported that
push-out strength may be influenced by a type of fiber post to a greater extent
than by a luting agent (Kurtz et al. 2003). Nevertheless, it was assumed that
combining all the fiber post system components (resin cement, adhesive and
fiber post) from the same manufacturer would prevent possible
incompatibility between the materials and allow assessing the full potential of
each system in laboratory conditions.
Significant differences were found between experimental groups
which led to the rejection of the null hypothesis. Both self-adhesive groups
were comparable with Calibra and MultiCore Flow etch-and-rinse groups.
135
This finding is in contrast with some previous investigations (Goracci et al.
2005; de Durao Mauricio et al. 2007; Wang et al. 2008). The favourable
push-out strength of RelyX Unicem may be partly explained by the fact that
in the present investigation it was used with RelyX Fiber Post. According to
the manufacturer’s claims, this post-cement system offers both chemical
compatibility and strong micromechanical post/cement interlocking. In
previous investigations RelyX Unicem was used with FRC Postec post
(Goracci et al. 2005; de Durao Mauricio et al. 2007), Aestheti Plus post
(RTD) (Wang et al. 2008) and C-Post (RTD) (Wang et al. 2008), which may
account for the discrepancy in the results. In the study by De Durao Mauricio
et al. (de Durao Mauricio et al. 2007), the vast majority of testing failures
was found between post and cement, and no failures were observed between
dentin and cement, which may imply unsatisfactory RelyX Unicem/FRC
Postec coupling. On the contrary, in the present study the majority of failures
were located between dentin and cement (Table 3). Furthermore, after the
initial 5 min period of self-curing RelyX Unicem was light-cured in the
present study, whereas in the previous investigations it was used only in the
self-cure mode (de Durao Mauricio et al. 2007; Wang et al. 2008). It was
reported that light curing significantly increased bond strength of RelyX
Unicem to various types of ceramics (Piwowarczyk et al. 2004; Piwowarczyk
et al. 2005). Taking into account the low degree of conversion of this cement
when it is self-cured (Kumbuloglu et al. 2004), it might be advisable to use it
in dual-cure mode.
Retention of quartz fiber posts cemented with dual-cure resin cement
RelyX ARC in combination with an etch-and-rinse adhesive was comparable
to the retention obtained with RelyX Unicem (Bateman et al. 2005) and these
findings are in accordance with the present investigation. Push-out strength
of Panavia F was significantly lower than RelyX Unicem push-out strength
136
and this result is consistent with previous reports (Bitter et al. 2006; Huber et
al. 2007). It is interesting to notice that cohesive failures within the luting
agent were only seen in the Panavia F 2.0 group. This may be the result of the
unfavourable cohesive strength of this cement.
MultiCore Flow is the material which is formulated to be used both as
the cement and core material. Its push-out strength in the present
investigation was comparable to Calibra. Having in mind the favourable
adhesion of this material to silanized FRC Postec post (Magni et al. 2007), its
clinical use could offer advantages. Besides the procedure being easier and
faster, it also results in less interfaces between different types of materials
and therefore in less potentially critical areas where failure could occur.
Although FluoroCore 2 is a core build-up material, it was included into this
investigation following the suggestion of the manufacturer, in order to
explore its potential use in luting fiber posts. However, its push-out strength
was significantly lower in comparison with Calibra (Table 3), even though
both materials were used with the same adhesive (XPBond). It may be
speculated that the application mode and higher viscosity of FluoroCore 2 in
comparison with Calibra precluded its close adaptation to root canal walls, as
FluoroCore 2 was applied to the post only, whereas Calibra was firstly
introduced into post space by a lentulo spiral.
This study assessed push-out strength of fiber posts after 24 hours of
water storage. It is possible that longer storage and/or thermal cycling would
give different results. Within the limitations of the present investigation, it
may be concluded that 24 h push-out strength of fiber posts was significantly
influenced by luting agents. The study findings do not allow favorizing any
of the three investigated adhesive approaches with certainty. Nevertheless, in
the test arrangement used, the self-etching approach may offer less
137
favourable adhesion to root canal dentin in comparison to etch-and-rinse and
self-adhesive approaches.
138
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Chapter 4: Light transmission through fiber post
4.1. Light transmission through fiber post: The effect on adhesion, elastic
modulus and hardness of dual-cure resin cement
Ivana Radovic, Gabriele Corciolani, Elisa Magni, Goranka Krstanovic,
Vladimir Pavlovic, Zoran R. Vulicevic, Marco Ferrari. Dental Materials
2009; 25(7): 837-844.
Introduction
The use of fiber post and core systems has been extensively investigated and
supported by clinical (Bitter and Kielbassa 2007; Cagidiaco et al. 2008) and
laboratory studies (Bitter and Kielbassa 2007; Goracci et al. 2007). In order
to allow for optimal retention and favorable stress distribution inside the root
canal (De Santis et al. 2000), resin-based luting agents are indicated for fiber
post cementation (Goracci et al. 2007).
Light curing resins are not recommended for fiber post cementation
because of inadequate depth of cure in the apical portions of the root, even if
translucent posts are used (Roberts et al. 2004). Therefore, dual-cured and
self-cured resin cements have been advised for fiber post cementation. Dual-
cured resin cements have been widely used by the clinicians and were
investigated in a number of clinical studies (Ferrari et al. 2000; Monticelli et
al. 2003; Grandini et al. 2005; Naumann et al. 2005a; Naumann et al. 2005b;
Cagidiaco et al. 2007; Ferrari et al. 2007; Naumann et al. 2007). These
cements are expected to adequately polymerize in areas which cannot be
entirely reached by light as well as in complete absence of light.
Nevertheless, it was reported that in the absence of light some dual-cured
145
cements may not reach an adequate degree of conversion (Caughman et al.
2001; Kumbuloglu et al. 2004). Therefore, light curing was recommended for
dual-cured resin cements. Having in mind the depth of post space
preparations, translucent fiber posts were introduced in order to facilitate
light curing. Adequate curing is considered to be especially important in the
apical portions of the root canals which have presented impaired adhesion in
the vast number of studies that dealt with differences in adhesion along the
post space (Goracci et al. 2007).
Recent investigations pointed out that the amount of transmitted light
differs between different fiber posts. Limited or no light transmission was
recorded through some fiber posts that were claimed to be translucent by the
manufacturers (Teixeira et al. 2006; dos Santos Alves Morgan et al. 2008;
Goracci et al. 2008). A significant reduction of the quantity of transmitted
light as the depth increased was also reported (dos Santos Alves Morgan et
al. 2008). Concern was raised regarding the ability of fiber posts to transmit
light in the amount sufficient for polymerization of dual-cured resin cements
in the apical portion of the post space.
No attempt was made in the literature so far to investigate the effect
of fiber post light transmitting ability to the adhesive potential of dual-cured
resin cements used for post cementation. One study investigated the influence
of fiber post translucency on the degree of conversion of dual-cured resin
cement (Faria e Silva et al. 2007). The use of non light transmitting carbon
fiber post resulted in lower degree of conversion at medium depth of the post
space in comparison to translucent fiber post (Faria e Silva et al. 2007). It
may be assumed that the amount of light transmitted through the post affects
dual-cured resin cement’s coupling to root dentin and fiber post, as well as
micromechanical properties of the cement itself. Therefore, the aim of this
study was: 1. to determine the light transmission at different post levels and
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at the apical tip through two fiber posts that differ in light-conducting aspect
by taking spectrophotometric measurements; 2. to investigate whether the
type of fiber post influences the continuity of resin cement-root dentin (C-
RD) and resin cement-fiber post (C-FP) interface, keeping all other variables
constant; 3. to investigate whether the type of fiber post influences the elastic
modulus and hardness of the cement layer. The null hypothesis was that there
are no statistically significant differences in the continuity of C-RD/C-FP
interface and in elastic modulus/hardness of the cement layer following the
cementation of two fiber posts with different light transmitting properties.
Materials and methods
Measurements of light transmission through the posts
A pilot investigation was firstly conducted in order to select two fiber posts
that differ in light transmission. Several fiber posts that are claimed by the
manufacturers to transmit light were used. Each post was placed
perpendicular through a black cardboard taken from the Q-14 color
separation scale (Kodak Co, Rochester, USA). The distance between the card
and the apical tip of each post was set at 10 mm and light curing unit
(L.E.Demetron 1, Kerr, Danbury, CT, USA) was placed on the opposite end
of the post. Two fiber posts that appeared to differ the most in the amount of
light that could be visually observed below the black cardboard were then
selected for further investigation.
Two groups were formed according to the fiber post investigated. Ten
posts were used in each group.
Group 1: Tech 21 X-OP fiber post #12 (Isasan, Rovello Poro, Italy) which
consists of silica-zirconia fibers (55%), diphenilpropane and methyloxirane
(45%). Its coronal diameter is 1.2 mm and its apical diameter is 0.8 mm.
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Group 2: DT Light Post #2 (RTD, St Egreve, France) which consists of
epoxy resin (40%), and quartz fibers (60%). Its coronal diameter is 1.8 mm
and its apical diameter is 1 mm.
Each post was placed through a black cardboard in the same manner
as in pilot investigations. The system light-curing unit/post was positioned on
a stand. A 50 �m fiber optic (P50-2-UV-VIS, Ocean Optics, FL, USA)
connected to a Spectrophotometer (PSD1000, Ocean Optics, FL, USA) was
oriented perpendicular to the post and stabilized. The fiber was placed at
three different levels along the post - 2mm, 5 mm and 8 mm from the apical
tip (Figure 1 A), and at the tip of the post (Figure 1 B). These distances were
always verified by an electronic digital caliper with a 10 �m resolution (1651
DGT, Beta, Milan, Italy).
The spectrophotometer was connected to a computer running
spectrum analyzer software (OOIBase 32, Ocean Optics, FL, USA). The
software was set in “Scope” mode, in order to evaluate the light counts that
correlated to the amount of photons received from the Charge Coupled
Device detector of the spectrophotometer. At 470 nm, for each count 30
photons were received from the detector of the instrument.
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Figure 1: Schematic drawing of the test set-up for the measurements of light
transmission through the posts. Each post was placed through a black
cardboard. The distance between the card and the apical tip of each post was
set at 10 mm and light curing unit was placed on the opposite end of the post.
A 50 �m fiber optic connected to a Spectrophotometer was oriented
perpendicular to the post and stabilized. The fiber was placed at three
different levels along the post - 2mm, 5 mm and 8 mm from the apical tip
(A), and at the tip of the post (B).
Counts were recorded at each level. In both groups a radiometer was used
prior to measurements (Optilux Radiometer, sds/Kerr, Orange, CA, USA) in
order to check that the output of the light tip (Light Guide Curved 11mm
1020898, Kerr, Danbury, CT, USA) remained over 700 mW/cm2.
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Specimen preparation for interface observations
Twenty intact single-rooted human premolars, extracted due to orthodontic
reasons, were selected for the study. The teeth were stored in 1% chloramine
T at 4°C for no more than six months until use. The crown of each tooth was
removed at 1mm above the cement-enamel junction, using a slow speed
diamond saw (Isomet, Buehler, Lake Bluff, IL, USA) under water-cooling.
A crown-down preparation technique was followed, using stainless
steel K-files (Union Broach, New York, NY) combined with 2.5% sodium
hypochlorite irrigation. The canals were filled with gutta-percha and a sealer
(Acroseal, Septodont, Saint Maur Des Fosses, France; batch R1 077, R1 081)
following the lateral condensation technique. The filled roots were coronally
sealed with glass ionomer cement (Fuji IX, GC Corporation, Tokyo, Japan;
batch 0711071) and stored in water for 48 hr to allow the sealer to set. The
roots were then divided into two experimental groups (n=10) according to the
fiber post used.
Group 1: Tech 21 X-OP fiber post #12
Group 2: DT Light Post #2.
After removing the temporary coronal seal, 8-mm post space was
prepared in each root with drills provided by post manufacturers. In both
groups, XPBond Dual Cure adhesive system was used (XPBond and Self-
Cure Activator; Dentsply Caulk, Milford, DE, USA; batch 0604001288) in
combination with the dual-cure resin cement Calibra (Dentsply Caulk; batch
base 060112, batch catalyst 060605). Caulk 34% Tooth Conditioner Gel
(34% phosphoric acid; Dentsply Caulk) was applied to the post space through
a needle, and after 15 seconds it was completely rinsed off with water carried
into the canal with an endodontic syringe. Excess water was removed from
the post space with a gentle air blast. Paper points were used to remove
residual moisture. XPBond was mixed with Self-Cure Activator following
150
the manufacturer’s instructions. The adhesive/activator mixture was applied
to post preparation with a microbrush, maintaining the contact of
adhesive/activator with tooth structure for 20 seconds. The adhesive/activator
solution in excess was absorbed from the post space by a paper point and
light-cured for 40s (L.E.Demetron 1). Resin cement components were mixed
and introduced into the post preparation with a lentulo spiral. The post was
seated immediately and the excess was removed. Light-curing was performed
through the post for 40 seconds. The exposed dentin along the coronal part of
the root was covered with flowable composite (Tetric Flow, Ivoclar
Vivadent, Schaan, Liechtenstein; batch G08479). All the post-cemented roots
were placed in water at room temperature.
After 7 days each root was longitudinally cut through the post using a
low speed diamond saw (Isomet). Only one section per root was randomly
selected and used for interface evaluation, in order to allow that the sections
can be treated as independent statistical units. Sections were polished with
silicon carbide papers (600, 800, 1000, 1200) under running water and gently
decalcified for 15 seconds with silica-free phosphoric acid gel (Uni-Etch,
Bisco, Schaumburg). After rinsing with water and air drying, polyvinyl
siloxane (Elite HD+, Zhermack, Badia Polesine, Italy; batch 47233)
impressions of the surfaces to be observed were taken. Positive replicas were
then obtained using epoxy resin (i-pox plus, AuDent AG, Triesenberg,
Liechtenstein).
SEM interface observations
Each replica was mounted on a metallic stub, sputtered with gold (BAL-TEC
SC-RD 005, BAL-TEC AG, Balzers, Liechtenstein), and observed under a
scanning electron microscope (JSM-6390 LV, JEOL, Tokyo, Japan) at
different magnifications. Measurements were made using the JEOL’s image
151
analysis software directly on the sections in the microscope. Firstly the exact
length of the entire cement-dentin (C-RD) and cement-post (C-FP) bonding
interface was measured. The bonding interface on each side of the post was
further divided into coronal, middle and apical third. In each third gaps and
discontinuities at the C-RD and C-FP interface were measured. The integrity
of the interface in each third was then expressed as the percentage of the
continuous (gap-free) interface. The percentage of the continuous interface
along the entire C-RD and C-FP interface was also calculated.
Elastic modulus and hardness measurements
Three sections were randomly selected per group for the analysis of the
micromechanical properties of the cement layer in each third of the post-
space. The specimens were fixed to glass slabs with methacrylate resin
(Technovit 4004, Heraeus Kulzer, Wehrheim, Germany), with the flat surface
to be tested parallel to the slab. Prior to testing, the surfaces were polished
with 1 �m-polycrystalline diamonds (DP-Spray, P; Struers) under water
cooling. Modulus of elasticity (E) and Vickers hardness (VH) of the cement
layer were assessed. The measurements were performed by means of a micro
hardness indenter (Fischerscope H100C; Fischer, Sindelfingen, Germany). A
constant distance of 200 �m was maintained between the measurement
points, which were located from the most coronal to the most apical limits of
the post-space. The test procedure was carried out force controlled. The test
load increased and decreased at a constant speed between 0.4 mN and 500
mN. The force application time can be non-standardly varied. The force
increased from 0.4 mN to 500 mN in 20s, the maximal force of 500 mN was
kept constant for 5s, then the force decreased from 500 mN to 0.4 mN in 20s
and the minimal force of 0.4 mN was kept constant for 5s. The load and the
penetration depth of the indenter (Vickers pyramid: diamond right pyramid
152
with an angle �=136° between the opposite faces at the vertex) were
continuously measured during the load-unload-hysteresis.
The Universal Hardness is defined as the test force divided by the
apparent area of the indentation at maximal force. From a multiplicity of
measurements stored in a database supplied by the manufacturer, a
conversion factor between Universal Hardness and Vickers hardness (VH)
was calculated and implemented into the software, so that the measurements
were expressed in Vickers hardness units.
The indentation modulus was calculated from the slope of the tangent
of the indentation depth-curve at maximal force and is comparable with the
modulus of elasticity of the material (E).
Statistical analysis of the interface continuity data
Since the interface continuity data were not normally distributed
(Kolmogorov–Smirnov test, p<0.05), non-parametric statistical tests were
selected to assess significant differences. Mann Whitney U-test was applied
to compare DT Light Post to Tech 21 X-OP in the percentage of continuous
C-RD and C-FP interface in each third as well as in the percentage of
continuity along the entire two interfaces. Wilcoxon signed ranks test was
used to compare the percentage of continuous interface among the thirds for
each fiber post separately. Wilcoxon signed ranks test was also used to
compare C-RD to C-FP interface in each third and along the entire interface
for each of the two posts separately.
Statistical analysis of the elastic modulus and Vickers hardness data
Since the elastic modulus (E) and Vickers hardness (VH) data were normally
distributed (Kolmogorov–Smirnov test, p>0.05), parametric statistical tests
were selected. Repeated measures analysis of variance (ANOVA) was used
153
to compare E and VH measurements between the post space thirds for each
fiber post. Independent samples t-tests were used to compare E and VH
measurements between DT Light Post and Tech 21 X-OP in each post space
third. In all the statistical tests, the level of significance was set at p<0.05 and
calculations were handled by the SPSS 15.0 software (SPSS Inc.; Chicago,
IL, USA).
Results
Light transmission
No light transmission was detected through Tech 21 X-OP. For DT Light
Post light intensity decreased from the coronal to apical portion and peaked at
the apical tip (Table 1).
Table 1: Light transmission through Tech 21 X-OP and DT Light Post
Level Mean (counts)
Standard deviation (counts)
Tech 21 X-OP Coronal 0 0
Middle 0 0
Apical 0 0
Tip 0 0 DT Light Post Coronal 900 14.9
Middle 820 15.6
Apical 620 12.3
Tip 4096 0.0
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Interface continuity at C-RD interface
When two fiber posts were compared, Tech 21 X-OP specimens presented
significantly lower percentage of the continuous interface in the apical third
and along the entire interface (Table 2). The comparisons between the post
space thirds revealed that in Tech 21 X-OP apical third exhibited lower
percentage of continuous interface than coronal third. In DT Light Post group
no differences were found among the interface thirds. In both groups the gaps
at the C-RD interface were mostly located between the adhesive and the
cement (Figure 2 A). In some Tech 21 X-OP specimens conglomerates of
poorly polymerized adhesive and resin cement could be seen, particularly in
the apical third (Figure 2 B).
Interface continuity at C-FP interface
When two fiber posts were compared, Tech 21 X-OP specimens presented
significantly lower percentage of the continuous interface in the apical third
and along the entire interface (Table 2). DT Light Post specimens presented
no gaps at the C-FP interface (Table 2 and 3, Figure 3). The comparisons
between the post space thirds revealed no significant differences for neither
of the posts.
Comparisons between C-RD and C-FP interface for each fiber post
For Tech 21 X-OP, C-FP interface had a significantly higher percentage of
continuity than C-RD interface in middle and coronal third (Table 3). In DT
Light Post specimens, percentage of continuous C-FP interface along the
entire interface and in coronal third was significantly higher than the
percentage of the continuous C-RD interface.
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Table 2: Percentage of the continuous C-RD and C-FP interface. Numbers
are means; values in brackets are standard deviations. Groups marked with
the same superscript letters/symbols are not statistically significantly
different. Upper case letters indicate statistically significant differences at the
C-RD interface between two fiber posts for each root third and for the entire
cement-dentin interface (Mann-Whitney U test, p<0.05). Symbols indicate
statistically significant differences at the C-FP interface between two fiber
posts for each root third and for the entire cement-dentin interface (Mann-
Whitney U test, p<0.05). Lower case letters indicate statistically significant
differences within the column, i.e. between the post space thirds for each
fiber post, at C-RD and C-FP interface (Wilcoxon signed ranks test, p<0.05).
C-RD interface (%) C-FP interface (%)
Tech 21 X-OP DT Light Post Tech 21 X-OP DT Light Post Coronal third 87.56 (24.01)Aa 94.47 (4.73)Aa 93.69 (13.85)�a 100.00 (0.00)�a Middle third 68.96 (19.10)Aab 81.61 (25.65)Aa 92.97 (11.69)�a 100.00 (0.00)�a Apical third 58.47 (29.02)Ab 94.97 (8.52)Ba 75.97 (31.58)�a 100.00 (0.00)�a Entire interface 71.66 (22.60)A 90.35 (11.02)B 87.54 (12.50)� 100.00 (0.00)�
156
Table 3: Percentage of the continuous C-RD and C-FP interface. Numbers
are means; values in brackets are standard deviations. Groups marked with
the same superscript letters are not statistically significantly different. Letters
indicate statistically significant differences within the row, i.e. between C-RD
and C-FP interface in each root third and at the entire interface for each of the
two fiber posts (Wilcoxon signed ranks test, p<0.05).
C-RD interface (%)
C-FP interface (%)
Tech 21 X-OP
Apical third 58.47 (29.02)A 75.97 (31.58)A
Middle third 68.96 (19.10)A 92.97 (11.69)B
Coronal third 87.56 (24.01)A 93.69 (13.85)B
Entire interface 71.66 (22.60)A 87.54 (12,50)B
DT Light Post
Apical third 94.97 (8.52)A 100.00 (0.00)A
Middle third 81.61 (25.65)A 100.00 (0.00)A
Coronal third 94.47 (4.73)A 100.00 (0.00)B
Entire interface 90.35 (11.02)A 100.00 (0.00)B
157
Figure 2: SEM micrographs of Tech 21 X-OP specimens. A: the gaps at the
C-RD interface were most often located between the adhesive and the cement
while resin tags could be seen in dentinal tubules. B: In some Tech 21 X-OP
specimens areas of poorly polymerized adhesive and cement could be seen,
especially in the apical third. c: resin cement; d: dentin; r: resin tag.
A
B
158
Figure 3: SEM micrographs of DT Light Post specimens. A: In DT Light
Post specimens all the gaps were located at the C-RD interface (asterisk)
whereas C-FP interface was 100% continuous. c: resin cement; d: dentin; p:
fiber post.
B
A
159
Elastic modulus and Vickers hardness
E and VH decreased from coronal to apical for both fiber posts. Significant
differences in E and VH were found between the post space thirds (Table 4).
In Tech 21 X-OP specimens E and VH in middle and apical third were
significantly lower than in coronal third. For DT Light Post, no differences
were found between coronal and middle third in E and VH measurements,
whereas significantly lower E and VH were found in apical third. When two
fiber posts were compared, E was significantly lower in Tech 21 X-OP
specimens in all post space thirds. VH in coronal third did not significantly
differ between two fiber posts, while it was significantly lower in middle and
apical third in Tech 21 X-OP specimens (Table 5).
Table 4: Elastic modulus and Vickers hardness. Numbers are means; values
in brackets are standard deviations. Groups marked with the same superscript
letters are not statistically significantly different. Letters indicate statistically
significant differences within the column, i.e. between the post space thirds
for each fiber post (repeated measures ANOVA, p<0.05)
Tech 21 X-OP DT Light Post
Elastic modulus (GPa)
Vickers hardness (N/mm2)
Elastic modulus (GPa)
Vickers hardness (N/mm2)
9.60 (1.53)A 59.23 (15.32)A 10.75 (1.51)A 63.12 (13.79)A
8.70 (2.40)B 42.27 (11.36)B 10.91 (1.18)A 61.57 (12.58)A
5.88 (1.60)C 37.62 (11.57)B 9.69 (1.18)B 49.09 (11.80)B
160
Table 5: Elastic modulus and Vickers hardness. Numbers are means; values
in brackets are standard deviations. Groups marked with the same superscript
letters are not statistically significantly different. Letters indicate statistically
significant differences within the row, i.e. between Tech 1 X-OP and DT
Light Post in each post space third (independent samples t-test, p<0.05).
Post space third Tech 21 X-OP DT Light Post
Elastic modulus (GPa)
Coronal 9.60 (1.53)A 10.75 (1.51)B
Middle 8.70 (2.40)A 10.91 (1.18)B
Apical 5.88 (1.60)A 9.69 (1.18)B
Vickers hardness (N/mm2)
Coronal 59.23 (15.32)A 63.12 (13.79)A
Middle 42.27 (11.36)A 61.57 (12.58)B
Apical 37.62 (11.57)A 49.09 (11.80)B
161
Discussion
SEM method used in this study has been widely used for investigation of
adhesion in root canals following cementation of fiber posts (Vichi et al.
2002a; Vichi et al. 2002b; Grandini et al. 2004). In order to avoid possible
influence of shrinkage under vacuum in the SEM chamber on the presence of
gaps along the investigated interfaces, epoxy resin replicas were made.
Significant differences were found in the percentage of the continuous C-RD
and C-FP interface between the experimental groups. Likewise, elastic
modulus and microhardness of the cement layer were significantly influences
by the fiber post used. Therefore, the null hypothesis had to be rejected.
Both investigated fiber posts are claimed to transmit light by the
manufacturers. Nevertheless, no light transmission was detected through
Tech 21 X-OP. It is possible that the presence of silica-zirconia fibers in Tech
21 X-OP fiber post adversely influenced its light transmitting properties. In
the previous investigation of fiber post light transmission that used the same
spectrophotometric method as the present study, somewhat lower readings
were recorded for DT Light Post (Goracci et al. 2008). Nevertheless, the
same trend of reduction in light transmission from coronal to apical, followed
by the increase at the tip of the posts was found. Previous study investigated
DT Light Post size 1, whereas size 2 was used in the present study. The
difference in sizes as well as variations in composition of posts originating
from two different batches may clarify the difference in spectrophotometric
counts that were recorded.
The occurrence of gaps in general may be related to the high C-factor
in bonded root canals (Tay et al. 2005). The lower percentage of continuous
C-RD and C-FP interface in Tech 21 X-OP specimens may be the
consequence of the lack of light transmission through this fiber post. The
162
absence of light may have impaired complete polymerization of the cement
(Figure 2 B), particularly in the apical third, and may have adversely affected
its coupling with root dentin and post surface. Resin cement polymerization
in the apical third relied solely on chemical catalysts. This may clarify the
significantly lower percentage of continuous C-RD interface in Tech 21 X-
OP specimens in comparison to coronal third that was accessible to light
(Table 2).
On the other side, no regional differences were found along the C-RD
interface in DT Light Post specimens. Spectrophotometric measurements
revealed a reduction in light transmission from coronal to apical third of this
fiber post. Nevertheless, a considerably high peak in counts was measured at
the tips of the posts. This may be explained by the unidirectional longitudinal
orientation of the reinforcing quartz fibers that could facilitate the
transmission of light up to the tip of the post. Therefore, light could
participate in resin cement polymerization in the apical third in a manner
similar to coronal third. The presence of light in the apical third may thus
clarify the lack of regional differences along the C-RD interface in DT Light
Post specimens.
The absence of gaps at C-FP interface in DT Light Post specimens
indicates more predictable adhesion at the post-cement in comparison to
cement-dentin level. In Tech 21 X-OP specimens no difference in continuity
of the entire interface was found between C-RD and C-FP interface. Apart
from differences in post surface properties between the two posts that may
have affected adhesion to resin cement, it may be speculated that light
transmission contributed to favorable post-cement coupling in DT Light Post
specimens.
Markedly lower percentage of continuous resin cement-root dentin
interface was reported in the study that investigated cementation of Fibrekor
163
fiber post (Jeneric Pentron Incorporated, Wallingford, CT, USA) with a self-
cured, dual-cured and light-cured resin cement, using a similar method as in
the present study (Bonfante et al. 2008). The authors of the present study
believe that this difference in case of dual-cured and light-cured cement may
be partly attributed to the lack of light transmitting ability of Fibrekor fiber
post (Teixeira et al. 2006). However, it remains unclear why cementation of
Fibrekor post with a self-cured cement did not result in a higher percentage
of the continuous C-RD interface (Bonfante et al. 2008). A reduction in
interface continuity from coronal to apical third was also reported (Bonfante
et al. 2008), which is in accordance with the present study.
Universal occurrence of interfacial gaps was also reported when
carbon fiber posts Tech 2000 (Isasan) and Endopost (RTD) were cemented
using dual-cured resin cements (Pirani et al. 2005). The percentage of
continuous interface was not reported in this study (Pirani et al. 2005) which
precludes direct comparisons with the present study. Nevertheless, it may be
speculated that the lack of light transmission through carbon fiber posts
contributed to the high incidence of gaps.
E and VH decreased from coronal to apical for both fiber posts. This
finding correlates with previous study that evaluated hardness of dual-cured
resin cement used for the cementation of DT Light Post (Teixeira Cda et al.
2008). However, in Tech 21 X-OP specimens, significant differences in
comparison to coronal third were found in middle third of the post space
already. On the other side, coronal and middle third in DT Light Post
specimens were comparable, whereas only measurements in the apical third
were significantly lower. Moreover, E and VH were significantly higher
when DT Light Post was used. Superior micromechanical properties of resin
cement in DT Light Post specimens may be attributed to the enhanced
cement polymerization in the presence of light. It was previously reported
164
that composite resin micromechanical properties may serve as an indicator
for the extent of monomer conversion (Ferracane 1985; Rueggeberg and
Craig 1988; Bouschlicher et al. 2004). Therefore, the results of hardness
measurements performed in this study indirectly indicate that higher degree
of conversion of dual-cured resin cement may be attained by the use of light
transmitting fiber post.
The authors are aware that the specific choice of dual-cured resin
cement might have influenced the results of the present study. It is possible
that adhesion of different resin cement to root dentin in terms of the
percentage of continuous C-RD and/or C-FP interface would not be
influenced by the type of fiber post and its light transmitting ability.
Conclusion
In conclusion, cementation of fiber post with no light transmitting ability
using dual-cured resin cement resulted in lower percentage of continuous C-
RD and C-FP interface in comparison to cementation of light transmitting
fiber post. Elastic modulus and Vickers hardness of the cement layer
significantly decreased from coronal to apical third of the post space
regardless of the fiber post used. However, cementation of light transmitting
fiber post resulted in higher elastic modulus and Vickers hardness of the
cement layer in comparison to cementation of fiber post with no light
transmitting ability.
165
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Summary
This thesis aimed at assessing three aspects related to fiber post cementation:
post surface treatment, the type of resin cement used for cementation and
light transmission through the post. It was hypothesized that these aspects
may influence cementation success. In order to verify author’s assumptions,
several laboratory investigations were performed. The thesis consists of four
chapters in which six studies are presented.
Chapter 1 covers general introduction to the main topic. The use of
fiber posts in endodontically treated teeth was presented. Basic features of
fiber posts, such as composition, elasticity and esthetics were discussed, as
well as clinical benefits that these features provide. Indications in which fiber
posts may show their full potential were described, including the specific
benefits of fiber posts use in pediatric dentistry and traumatology. Even
though all fiber posts available to clinicians consist of same basic
components, mechanical properties and clinical behavior of different brands
may vary substantially. Therefore, some factors that may influence the choice
of fiber post were presented. Besides the three aspects of fiber post
cementation that this thesis focused on, several other factors are believed to
influence the success of fiber post cementation. The following factors were
briefly discussed in Chapter 1: the type of endodontic sealer, the amount of
remaining coronal dentine, ferrule preparation and resin cement thickness.
Fiber post surface preparation and its influence to adhesion between
fiber posts and resin cements were assessed in Chapter 2. This chapter
consists of three studies in which microtensile bond strength between posts
and resin cements was investigated following various treatments of fiber post
surface. SEM observations of treated/untreated fiber post surfaces and
adhesive interfaces were performed as well. The first study evaluated the
170
influence of sandblasting pretreatment and different “chair-side” treatments
of methacrylate based fiber posts on the microtensile bond strength with a
dual-cured resin composite. The focus of the second study was the influence
of surface treatments of epoxy resin-based fiber posts to microtensile bond
strength with resin cement and flowable composite. Dual-cured adhesive was
applied to all posts in this study as this treatment had been shown to
effectively increase bond strength to epoxy resin-based fiber posts. The study
had two objectives: 1. to investigate whether previous sandblasting of the post
surface influences post-composite bond strength; 2. to evaluate the influence
of water storage on adhesive-mediated FRC post-resin cement and FRC post-
flowable composite bonds using a model of accelerated aging. In the third
study of Chapter 2, the aim was to evaluate the influence of an experimental
industrial treatment and conventional “chair-side” treatments of epoxy resin-
based fiber post surface on the microtensile bond strength to luting resin
cements. The experimental industrial treatment comprised two main steps: a
1�m-thick coating of zirconium oxide followed by silanization with 3–
(trimethoxysilyl) propyl methacrylate. This treatment was claimed to keep the
initial surface roughness of the fiber post in order to provide micromechanical
retention and to create a chemical bond between the silane and the adhesive
or cement. Conventional “chair-side” treatments that were performed in this
study were silane coating and adhesive application, whereas no treatment was
performed in the control group. Apart from SEM observations of
treated/untreated fiber post surfaces and adhesive interfaces, the surface of the
industrially coated posts was also examined using Energy Dispersive
Analysis by X-ray (EDAX) in a scanning electron microscope.
Resin cements and adhesive approaches for fiber post cementation
were the theme of Chapter 3, which consists of two studies. Particular
attention was given to self-adhesive cements as the newest and least
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investigated group of materials. The first study of Chapter 3 is a literature
review that aimed at summarizing research conducted on self-adhesive
cements and at providing information on their properties, based on the results
of original scientific full-papers from peer-reviewed journals listed in
PubMed. The results were summarized into the following categories:
adhesion to tooth substrates (enamel, dentin, root dentin), adhesion to
restorative materials (endodontic posts, ceramics, titanium abutments),
marginal adaptation, microleakage, mechanical properties, biocompatibility,
chemical adhesion and fluoride release, ratings in clinical use. The second
study of Chapter 3 investigated the adhesion of fiber posts cemented to root
dentin with luting agents that utilize three currently available adhesive
approaches. It was assumed that the simpler, self-etching and self-adhesive
approaches are equally effective as the clinically proven etch-and-rinse
approach. In order to assess the adhesion of fiber posts, thin-slice push-out
test was used.
In Chapter 4 a study which focuses on importance of light
transmission through the post is presented. This study investigated whether
light transmission through fiber posts influences the adhesive potential of
dual-cured resin cement used for post cementation, as well as
micromechanical properties of the cement itself. Firstly spectrophotometric
measurements were taken to determine the light transmission at different post
levels and at the apical tip through two fiber posts that appeared to differ
substantially in light-conducting aspect based on visual observation. The
measurements detected no light transmission through one of the posts,
whereas for the other one light intensity decreased from the coronal to apical
portion and peaked at the apical tip. Following the measurements, it was
investigated whether the type of fiber post influences the continuity of resin
cement-root dentin and resin cement-fiber post interface, keeping all other
172
variables constant. Moreover, it was assessed whether the type of fiber post
influences the elastic modulus and hardness of the cement layer.
Conclusions
The following conclusions may be drawn from the basic evaluation of the
following aspects related to fiber post cementation - post surface treatment,
the type of resin cement used for cementation and light transmission through
the post:
1. Sandblasting may give an increase in microtensile strength to
methacrylate-based glass fiber posts, eliminating the need to apply
additional ‘‘chair-side’’ treatments. Reducing the number of clinical steps
could contribute to simplify the clinical procedures.
2. Sandblasting followed by adhesive application may improve immediate
bond strength to epoxy resin-based fiber posts in comparison to the
adhesive alone. Fiber post-resin cement and fiber post-flowable composite
bonds may be impaired by accelerated water aging if mediated by
hydrophilic adhesive coatings.
3. The experimental industrial surface treatment and the adhesive application
enhance fiber post to resin cement interfacial strength. Industrial treatment
may simplify the clinical luting procedure. Cementation of epoxy resin-
based fiber posts without any treatment of the post surface is not
recommended.
4. Self-adhesive cements appear to offer a promising new approach in
indirect restorative procedures, including fiber post cementation. However,
the vast majority of available literature data is based on studies that
investigated only one of the cements that are currently available to
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clinicians. More importantly, long term clinical performance of these
materials needs to be assessed prior to making a general recommendation
for their use in fiber post cementation.
5. 24 h push-out strength of fiber posts was significantly influenced by luting
agents. This thesis findings do not allow favorizing any of the three
investigated adhesive approaches with certainty. Nevertheless, in the test
arrangement used, the self-etching approach may offer less favorable
adhesion to root canal dentin in comparison to etch-and-rinse and self-
adhesive approaches.
6. Cementation of fiber post with no light transmitting ability using dual-
cured resin cement resulted in lower percentage of continuous cement-root
dentin and cement-fiber post interface in comparison to cementation of
light transmitting fiber post.
7. Elastic modulus and Vickers hardness of the cement layer significantly
decreased from coronal to apical third of the post space regardless of the
light transmitting ability of fiber post used. However, cementation of light
transmitting fiber post resulted in higher elastic modulus and Vickers
hardness of the cement layer in comparison to cementation of fiber post
with no light transmitting ability.
Sommario e conclusioni
Questa tesi ha avuto lo scopo di valutare tre aspetti relativi alla cementazione
del perno in fibra: il trattamento di superficie del perno, il tipo di cemento
resinoso utilizzato per la cementazione e la trasmissione della luce attraverso
il perno. Allo scopo di verificare l’influenza di questi aspetti sul successo
della cementazione, sono stati condotti diversi studi di laboratorio. La tesi
consiste in quattro capitoli nei quali sono presentati sei studi.
174
Il Capitolo 1 contiene un’introduzione generale all’argomento della
tesi. Viene descritto l’uso dei perni in fibra nei denti trattati
endodonticamente. Le caratteristiche di base dei perni in fibra come la
composizione, l’elasticità e l’estetica sono discusse, così come i benefici
clinici apportati da queste caratteristiche. Vengono descritte le indicazioni
nelle quali i perni in fibra possono mostrare il loro pieno potenziale, compresi
i benefici specifici derivanti dall’uso dei perni in fibra in pedodonzia e in
traumatologia. Nonostante tutti i perni in fibra a disposizione del clinico
presentino gli stessi componenti di base, le proprietà meccaniche e il
comportamento clinico di perni di varie marche possono variare in modo
significativo. Vengono pertanto presentati alcuni fattori che possono
influenzare la scelta del perno in fibra. Oltre ai tre aspetti relativi alla
cementazione del perno in fibra su cui si basa questa tesi, molti altri fattori
sono ritenuti influenzare il successo della cementazione. I seguenti fattori
vengono brevemente discussi nel Capitolo 1: il tipo di cemento endodontico,
la quantità di dentina coronale residua, l’effetto ferula e lo spessore del
cemento resinoso.
La preparazione della superficie del perno e la sua influenza
sull’adesione tra perno in fibra e cementi resinosi sono stati valutati nel
Capitolo 2. Questo capitolo consiste di tre studi in cui è stata misurata la
forza di adesione microtensile tra perni e cementi resinosi in seguito a diversi
trattamenti di superficie del perno in fibra. Sono state condotte anche
osservazioni SEM delle superfici trattate/non trattate così come delle
interfacce adesive. Il primo studio ha valutato l’influenza della sabbiatura
come pretrattamento del perno e di differenti trattamenti “alla poltrona” di
perni in fibra a base di metacrilato sulla forza di adesione microtensile con
una resina composita duale. L’obiettivo del secondo studio è stato quello di
valutare l’influenza di trattamenti di superficie di perni a base di resina
175
epossidica sulla forza di adesione microtensile con cemento resinoso e
composito fluido. Un adesivo resinoso duale è stato applicato su tutti i perni
poiché questo trattamento è risultato essere efficace nell’aumentare la forza di
adesione ai perni epossidici. Lo studio ha avuto due obiettivi: 1. studiare se la
preventiva sabbiatura della superficie del perno è in grado di influenzare la
forza di adesione perno-composito; 2. valutare l’influenza della
conservazione in acqua sui legami mediati dall’adesivo tra perno-cemento
resinoso e perno-composito fluido usando un modello di invecchiamento
accelerato. Nel terzo studio del Capitolo 2, lo scopo è stato quello di valutare
l’influenza di un trattamento industriale sperimentale e di diversi trattamenti
“alla poltrona” della superficie di un perno a base di resina epossidica sulla
forza di adesione microtensile a cementi resinosi. Il trattamento industriale
sperimentale comprendeva due passaggi: un rivestimento di 1�m di ossido di
zirconio seguito dalla silanizzazione con 3-(trimetossisilil) propilmetacrilato.
Questo trattamento aveva lo scopo di migliorare l’iniziale ruvidità di
superficie del perno in fibra in modo da favorire una ritenzione
micromeccanica e di creare un’adesione chimica tra il silano e l’adesivo o il
cemento. I trattamenti convenzionali “alla poltrona” eseguiti in questo studio
erano la silanizzazione e l’applicazione di adesivo, mentre nessun trattamento
è stato eseguito nel gruppo controllo. Oltre alle osservazioni SEM delle
superfici dei perni trattate/non trattate e delle interfacce adesive, la superficie
dei perni rivestiti industrialmente è stata esaminata con analisi EDX (Energy
Dispersive by X-ray) in un microscopio elettronico a scansione.
I cementi resinosi e diverse strategie adesive per la cementazione del
perno in fibra sono stati il tema del Capitolo 3, il quale consiste di due studi.
Un’attenzione particolare è stata data ai cementi auto-adesivi come il più
nuovo e meno studiato gruppo di materiali dentali. Il primo studio del
Capitolo 3 è una revisione della letteratura volta a sintetizzare la ricerca
176
condotta sui cementi auto-adesivi e a fornire informazioni sulle loro proprietà,
in base ai risultati di lavori scientifici originali pubblicati su riviste impattate
presenti su PubMed. I risultati sono stati sintetizzati nelle seguenti categorie:
adesione ai substrati dentali (smalto, dentina, dentina radicolare), adesione ai
materiali da restauro (perni endodontici, ceramica, monconi di titanio),
adattamento marginale, microinfiltrazione, proprietà meccaniche,
biocompatibilità, adesione chimica e rilascio di fluoro, rilevanza clinica. Il
secondo studio del Capitolo 3 ha valutato l’adesione tra perni in fibra
cementati alla dentina intraradicolare con agenti che utilizzano tre attuali e
diverse strategie adesive. Si è stabilito che gli approcci più semplici, auto-
mordenzanti e auto-adesivi sono efficaci quanto la tecnica etch-and-rinse.
Allo scopo di determinare l’adesione dei perni in fibra, è stata usato il test di
push-out.
Nel Capitolo 4 viene presentato uno studio basato sull’importanza
della trasmissione della luce attraverso il perno. Questo studio ha valutato se
la trasmissione della luce attraverso i perni in fibra può influenzare il
potenziale adesivo del cemento resinoso duale usato per la cementazione del
perno, così come le proprietà meccaniche del cemento stesso. In primo luogo,
sono state effettuate misurazioni spettrofotometriche per determinare la
trasmissione della luce a diversi livelli del perno e in zona apicale in due
perni in fibra che sembravano differire in modo sostanziale riguardo alla
conduzione della luce ad un esame visivo. Le misurazioni non hanno
riscontrato alcuna trasmissione di luce in uno dei perni, mentre nell’altro
l’intensità della luce è diminuita dalla parte coronale a quella apicale del
perno, con un decremento significativo nella punta. Continuando le
misurazioni, si è studiato se il tipo di perno in fibra è in grado di influenzare
la continuità dell’interfaccia cemento resinoso-dentina radicolare e cemento
resinoso-perno in fibra, mantenendo costanti tutte le altre variabili. Inoltre, è
177
stato determinato se il tipo di perno in fibra influenza il modulo elastico e la
durezza dello strato di cemento.
Le seguenti conclusioni possono essere tratte dalla valutazione di base di
alcuni aspetti relativi alla cementazione del perno in fibra – trattamento di
superficie del perno, tipo di cemento resinoso utilizzato per la cementazione e
trasmissione di luce attraverso il perno:
1. La sabbiatura può aumentare la forza di adesione microtensile a perni in
fibra a base di metacrilato, eliminando la necessità di eseguire ulteriori
trattamenti “alla poltrona”. La riduzione del numero dei passaggi clinici
può contribuire alla semplificazione delle procedure cliniche.
2. La sabbiatura seguita dall’applicazione di adesivo può migliorare l’iniziale
forza di adesione a perni in fibra a base di resina epossidica rispetto all’uso
del solo adesivo. I legami perno in fibra-cemento resinoso e perno in fibra-
composito fluido possono essere compromessi da un invecchiamento
accelerato in acqua in presenza di adesivi idrofilici.
3. Il trattamento di superficie industriale sperimentale e l’applicazione di
adesivo migliorano la resistenza interfacciale del legame tra perno in fibra
e cemento resinoso. Il trattamento industriale può semplificare la
procedura clinica di cementazione. La cementazione dei perni in fibra a
base di resina epossidica senza alcun trattamento di superficie non è
raccomandata.
4. I cementi auto-adesivi sembrano rappresentare un approccio nuovo e
promettente nelle procedure di restauro indiretto, compresa la
cementazione dei perni in fibra. Tuttavia, la grande maggioranza dei dati
disponibili in letteratura è basata su studi che hanno valutato solo uno dei
cementi attualmente in commercio. Inoltre, il comportamento clinico a
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lungo termine di questi materiali deve essere valutato prima di poterli
consigliare per la cementazione del perno in fibra.
5. La resistenza push-out a 24 h dei perni in fibra è stata significativamente
influenzata dai cementi utilizzati. I risultati di questa tesi non consentono
di favorire con certezza nessuno dei tre approcci adesivi studiati. Tuttavia,
in questo test, l’approccio auto-mordenzante può portare ad una adesione
meno favorevole alla dentina radicolare rispetto agli approcci auto-adesivo
e etch-and-rinse.
6. La cementazione del perno in fibra senza trasmissione di luce usando un
cemento duale è risultato in una più bassa percentuale di continuità
all’interfaccia cemento-dentina radicolare e cemento resinoso-perno in
fibra rispetto alla cementazione di perni in grado di trasmettere la luce.
7. Il modulo elastico e la durezza Vickers dello strato di cemento è diminuita
in modo significativo dal terzo coronale a quello apicale del post space,
indipendentemente dalla capacità del perno nel trasmettere la luce.
Comunque, la cementazione del perno capace di trasmettere la luce è
risultato in un più alto modulo elastico e in una maggiore durezza Vickers
dello strato di cemento rispetto alla cementazione del perno in fibra senza
alcuna capacità di trasmissione di luce.
Sommaire et conclusions
La thèse vise d'examiner trois facteurs de cimentation des tenons
composites renforcés de fibres: préparatifs de la surface des tenons, type du
ciment composite destiné à la cimentation des tenons et la conductivité de
lumière par tenons. L'hypothèse de départ était que ces facteurs pourraient
influencer le succès de cimentation des tenons. Aux fins de vérifier
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l'hypothèse, plusieurs examens de laboratoire ont été effectués. La thèse
comprend quatre chapitres dans lesquels six études publiées sont présentées.
Chapitre 1 comprend une introduction au sujet principal.
L'application des tenons composites après le traitement endodontique des
dents y est présentée. Les caractéristiques fondamentales des tenons
composites, soit leur composition, leur élasticité et leur esthétique, ainsi que
les avantages cliniques fournis par ces caractéristiques. Les indications où les
tenons composites peuvent démontrer leur plein potentiel ont été décrites, y
compris les avantages spécifiques de ces tenons utilisés dans la dentisterie
pédiatrique et la traumatologie. Même si tous les tenons composites
comprennent les mêmes composantes de base, leurs caractéristiques
mécaniques et leur qualité peuvent considérablement varier dans les
conditions cliniques en fonction du producteur. Par conséquent, certains
facteurs pouvant influencer le choix du tenon y étaient présentées. Outre ces
trois aspects développés par la thèse, l'on considère qu'il y encore quelques
facteurs qui peuvent influencer le succès de cimentation des tenons. Dans le
Chapitre 1 la brève discussion concerne les facteurs suivants: le type de la
résine servant d'obturation définitive du canal radiculaire, la quantité restante
de la dentine coronaire, la préparation des viroles et l'épaisseur de la couche
du ciment composite.
Les préparatifs de la surface du tenon et son influence à l'adhérence
entre le tenon et le ciment composite ont été examinés dans le cadre de trois
études présentées dans le Chapitre 2. Dans ces études, après l'application de
différentes modalités de préparation de la surface du tenon, l'on a examiné la
puissance de liaison entre le tenon et le ciment par le teste de résistance à la
traction des micro-échantillons (“microtensile bond strength test”). Les
surfaces des tenons traités et de ceux non-traités étaient prises en
considération, ainsi que les interfaces adhérentes ciment-tenon au microscope
180
électronique à balayage (MEB). Dans la première étude l'on a examiné
l'influence de sablage et de différents procédés dans le cabinet, concernant les
préparatifs des tenons à matrice méthacrylique à la puissance de liaison avec
le composite double-polymérisé. Dans la deuxième étude il a été examiné
l'influence du préparatif du tenon à matrice en résine époxy à la puissance de
liaison avec le ciment composite et le composite liquide. L'adhésif double-
polymérisé était appliqué sur tous les tenons, étant donné qu'il a été déjà
constaté que ce traitement augmente, d'une manière efficace, la puissance de
liaison entre les matériaux composites et les tenons contenant la résine époxy.
Ces deux études ont eu deux objectifs: 1. de définir si le sablage avant
l'application de l'adhésif influence la puissance de liaison tenon-ciment et
tenon-composite liquide; 2. d'examiner l'influence de l'eau à la liaison tenon-
ciment et tenon-composite liquide, en utilisant le modèle de vieillissement
accéléré du matériau. L'objectif de la troisième étude du Chapitre 2 était
d'examiner l'influence des préparatifs expérimentaux industriels et de diverses
modalités des préparatifs au cabinet, de la surface du tenon à matrice en
résine époxy, à la puissance de liaison avec les ciments composites. Les
préparatifs expérimentaux industriels comprenaient deux pas: application de
la couche de l'oxyde de zirconium d'épaisseur de 1 �m et ensuite la
silanisation par 3- (trimethoxysilyl) propylméthacrylate. D'après les
confirmations du producteur, ces préparatifs assurent la rétention
micromécanique, ainsi que la liaison chimique entre le silane et l'adhésif ou le
ciment. Les procédés du cabinet relatifs aux préparatifs des tenons, examinés
dans cette étude comprenaient l'application du silane et l'application d'adhésif,
tandis que dans le groupe de contrôle la surface des tenons n'a pas subi aucun
traitement. Les surfaces des tenons traités et de ceux non-traités, ainsi que les
interfaces adhésives ciment-tenon étaiemt examinées au microscope (MEB).
La surface des tenons industriellement préparés a été également examinée par
181
l'analyse EDAX (Energy Dispersive Analysis by X-ray) au microscope
électronique à balayage.
Le sujet du Chapitre 3 concernait les ciments composites et divers
abords adhésifs qui peuvent être utilisés pour la cimentation des tenons
composites. Ce chapitre comprend deux études. Une attention particulière
était prêtée aux ciments composites auto-adhésifs qui font une catégorie la
plus récente et la moindre étudiée des ciments composites. La première étude
du Chapitre 3 est la revue de la littérature ayant pour objectif de donner les
informations sur les ciments composites auto-adhésifs en vertu d'études
scientifiques originales publiées dans les magasins recensés, indexées dans la
base PubMed. Les résultats sont classifiés dans les catégories suivantes:
adhésion avec les tissues dentaires (émail, dentine, dentine du canal
radiculaire), l'adhésion avec les matériaux de restauration (tenons
endodontiques, céramique, titane), adaptation marginale, micro-perméabilité,
propriétés mécaniques, biocompatibilité, adhésion chimique et échappement
des fluorure, l'évaluation de la qualité pendant utilisation clinique. La seconde
étude du Chapitre 3 a examiné l'adhésion des tenons composites, cimentés par
trois approches actuelles d'adhésion. L'hypothèse de départ était que les
approches simples, auto-adhésifs et automordançants sont aussi efficaces que
l'approche de mordançage total cliniquement confirmée. Aux fins d'examiner
l'adhésion des tenons, il a été fait le mesurage de rétention par le test des
découpes minces transversales (thin-slice push-out test).
Dans le Chapitre 4 il est présenté l'étude qui a examiné l'importance
de la conductivité lumineuse à travers le tenon. Y était examiné l'influence de
la conductivité lumineuse du tenon à l'adhésion du ciment composite à
double-polymérisé, ainsi qu'aux caractéristiques micromécaniques du ciment.
Par les mesurages spectrophotométriques, il a été défini la conductivité
lumineuse de deux tenons et se basant sur les observations visuelles, l'on a
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supposé qu'ils se distinguent essentiellement par cette caractéristique. Les
mesurages étaient effectués aux niveaux différents des tenons et à l'apex. Il a
été constaté l'absence de la conductivité lumineuse à travers un tenon parmi
deux, tandis qu'à travers le second tenon l'intensité de la lumière diminuait à
partir du niveau coronaire vers la région apicale, tandis qu'à la région apicale,
l'intensité était la plus élevée. Après les mesurages, il a été examiné
l'influence du type du tenon à la continuité de liaison adhésive ciment-dentine
et ciment-tenon. Il a été, également, examiné l'influence du type du tenon au
module d'élasticité et à la fermeté du ciment.
Se basant sur l'examen des facteurs suivants de cimentation des tenons
composites: préparatifs de la surface des tenons, type du ciment composite et
la conductibilité lumineuse des tenons, l'on peut faire les conclusions
suivantes:
1. Le sablage permet d'améliorer l'intensité de la liaison des matériaux
composites avec les tenons composites méthacryliques et d'éliminer le
besoin des traitements supplémentaires de la surface du tenon au cabinet.
La diminution du nombre des démarches cliniques donne sa contribution à
la simplicité des procédures cliniques.
2. Le sablage suivi d'application d'adhésif fait l'amélioration de l'intensité de
la liaison entre les matériaux composites (ciment et composite liquide)
avec les tenons composites en résine époxy, mesurée immédiatement après
la cimentation des tenons. La liaison adhésive des tenons préparés par
l'adhésif à ciment composite et le composite liquide peut être abîmée par
vieillissement accéléré dans l'eau.
3. Les préparatifs expérimentaux industriels et l'application des adhésifs
augmentent l'intensité de la liaison entre le ciment et le tenon composite
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avec la matrice en résine époxy. Le traitement industriel peut simplifier le
procédé clinique de cimentation. La cimentation des tenons composites
avec la matrice en résine époxy sans traitement de la surface des tenons
n'est pas recommandée.
4. Les ciments composites auto-adhésifs puissent offrir une nouvelle
approche prometteuse pour procédés indirects de restauration, y compris la
cimentation des tenons composites. Pourtant, la plupart des données de la
littérature sur ces ciments proviennent des recherches aux laboratoires d'un
des ciments étant actuellement à la disposition des cliniciens. Les études
cliniques de ces matériaux à long terme sont indispensables avant de
donner la recommandation générale pour l'utilisation des ciments auto-
adhésifs destinés à la cimentation des tenons.
5. La rétention des tenons composites, mesurée 24 heures après la
cimentation était considérablement différente par rapport aux diverses
ciments composites. En vertu des résultats de la thèse, il n'est pas possible
de constater avec certitude qu'une sur trois approches adhésives donne des
résultats meilleurs par rapport à deux autres approches. Pourtant, la
méthode utilisée a permis de constater une plus mauvaise adhésion des
tenons en utilisant l'approche d'automordançage par rapport à la méthode
autoadhésive et à celle de mordançage totale.
6. Le pourcentage de liaison adhésive continue ciment-dentine et ciment-
tenon été considérablement plus élevé après la cimentation du tenon qui
laisse passer la lumière par rapport au tenon qui ne la laisse pas.
7. Le module d'élasticité et de dureté du ciment d'après Vickers ont
considérablement baissé à partir du niveau coronaire vers la région apicale,
nonobstant la conductivité lumineuse des tenons. Pourtant, le module
d'élasticité et de dureté d'après Vickers étaient considérablement plus
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élevés après la cimentation des tenons à conductivité lumineuse par
rapport au tenon qui n'a pas la capacité de conduire la lumière.
Zusammenfassung und schlussfolgerungen
Diese Dissertation hatte das Ziel drei Aspekte, die mit der Zementierung von
Faserstiften im Zusammenhang sind, festzustellen: die Behandlung der
Oberfläche des Faserstiftes, der Resin-Zement, der für die Zementierung
angewendet wird, und die Lichtdurchlässigkeit durch den Faserstift. Es
wurde angenommen, dass diese Aspekte den Erfolg der Zementierung
beeinflussen könnten. Verschiedene Labor-Studien wurden durchgeführt, um
diese Annahmen zu bestätigen. Diese Dissertation besteht aus vier Kapiteln,
in denen sechs Studien dargestellt wurden.
Im Kapitel 1 gibt es eine allgemeine Einleitung über das Hauptthema.
Die Anwendung von Faserstiften in endodontisch behandelten Zähnen wurde
dargestellt. Die wesentlichen Eigenschaften der Faserstifte - wie die
chemische Zusammensetzung, die Elastizität und die Ästhetik - wurden
diskutiert so wie die klinischen Vorteile, die diese Eigenschaften anbieten.
Die klinischen Indikationen, in denen die Faserstifte ihres totale Potenzial
zeigen können, wurden beschreibt und die spezifischen Vorteile der
Anwendung der Faserstifte in der Kinderzahnheilkunde und in der
Traumatologie wurden aufgenommen. Auch wenn alle Faserstifte, die zur
Verfügung für die Zahnärzte stehen, aus den gleichen wesentlichen
Komponenten bestehen, können die mechanischen Eigenschaften und das
klinische Verhalten verschiedener Arten von Faserstiften beträchtlich
variieren. Daher wurden einige Faktoren, die die Auswahl des Faserstiftes
beeinflussen können, dargestellt. Außer den drei Aspekten der Zementierung
der Faserstifte, auf die diese Dissertation sich konzentrierte, sind andere
185
Faktoren gedacht, den Erfolg der Zementierung der Faserstifte zu
beeinflussen. Die folgenden Faktoren wurden im Kapitel 1 kurz diskutiert:
die Art des Wurzelfüllmaterials, die Menge des restlichen Kronendentins, die
Ferrule-Vorbereitung und die Dicke des Resin-Zementes.
Die Behandlung der Oberfläche des Faserstiftes und ihr Einfluss auf
die Adhäsion zwischen Faserstiften und Resin-Zementen wurden im Kapitel
2 festgestellt. Dieses Kapitel besteht aus drei Studien, in denen die
Microtensile-Verbundfestigkeit zwischen Faserstiften und Resin-Zementen
nach verschiedenen Behandlungen der Oberfläche der Faserstifte erforscht
wurde. Beobachtungen der behandelten/unbehandelten Oberfläche des
Faserstiftes und der adhäsiven Schnittstellen wurden auch mit einem REM
ausgeführt. Die erste Studie hat den Einfluss von dem Sandstrahlen und von
verschiedenen „Chair-Side“ Behandlungen auf die Microtensile-
Verbundfestigkeit zwischen Methacrylat-Faserstiften und einem
dualhärtenden Komposit-Zement bewertet. Das Thema der zweiten Studie
war der Einfluss von den Behandlungen der Oberfläche des Faserstiftes auf
die Microtensile-Verbundfestigkeit zwischen Epoxydharz-Faserstiften und
einem Resin-Zement bzw. einem Flowable-Komposit. Ein dualhärtendes
Adhäsiv wurde in dieser Studie auf allen Faserstiften appliziert, weil es
gezeigt worden war, dass diese Behandlung die Verbundfestigkeit mit den
Epoxydharz-Faserstiften erhöhte. Die Studie hatte zwei Ziele: 1. es zu
untersuchen, ob das Sandstrahlen der Oberfläche des Faserstiftes die
Verbundfestigkeit zwischen Faserstiften und Komposit-Zement beeinflusst;
2. den Einfluss der Wasserlagerung auf die von dem Adhäsiv vermittelte
Verbindung zwischen FRC Faserstiften und Resin-Zement und zwischen
FRC Faserstiften und Flowable-Komposit mit einem „Model of accelerated
Aging“ zu bestimmen. Das Ziel der dritten Studie vom Kapitel 2 war es, den
Einfluss von einer experimentellen industriellen Behandlung und von
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konventionellen „Chair-Side“ Behandlungen der Oberfläche von
Epoxydharz-Faserstiften auf die Microtensile-Verbundfestigkeit mit Resin-
Zementen festzustellen. Die experimentelle industrielle Behandlung bestand
aus zwei Schritten: eine 1�m-dicke Zirkoniumoxid-Schicht, die von der
Silanisierung mit 3-(Trimethoxysilyl) Propyl Methacrylat gefolgt wurde. Es
wurde behauptet, dass diese Behandlung den anfänglichen Rillenabstand des
Faserstiftes erhielt, um mikromechanische Retention anzubieten und um eine
chemische Verbindung zwischen dem Silan und dem Adhäsiv bzw. dem
Zement herzustellen. Die konventionellen „Chair-Side“ Behandlungen, die in
dieser Studie angewendet wurden, waren die Silanisierung und die
Anwendung eines Adhäsives. Dagegen wurde keine Behandlung in der
Kontrolle-Gruppe verwendet. Außer den REM Beobachtungen der
behandelten/unbehandelten Oberfläche des Faserstiftes und der adhäsiven
Schnittstellen wurde die Oberfläche der industriell behandelten Faserstifte
auch mit der „Energy Dispersive Analysis by X-Ray (EDAX)“ in einem
REM bewertet.
Resin-Zemente und adhäsive Techniken für die Zementierung der
Faserstifte waren die Themen vom Kapitel 3, das aus zwei Studien besteht.
Die selbst-adhäsiven Zemente wurden besonders berücksichtigt, weil sie die
neuesten und weniger untersuchten Gruppe von Materialien sind. Die erste
Studie vom Kapitel 3 ist eine Literaturübersicht, die das Ziel hatte, die
Forschung über die selbst-adhäsiven Zemente zusammenzufassen und
Auskunft über ihre Eigenschaften zu geben. Sie stützte sich auf die
Ergebnisse wissenschaftlicher Artikel von „peer-reviewed“ Zeitschriften, die
in Pub-Med gelistet sind. Die Ergebnisse wurden in den folgenden
Kategorien zusammengefasst: Adhäsion mit den Zahnhartsubstanzen
(Schmelz, Kronendentin, Wurzeldentin), Adhäsion mit den Restauration-
Materialien (Wurzelstifte, Keramik, Titanium-Abutments), marginale
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Anpassung, Microleakage, mechanische Eigenschaften, Biokompatibilität,
chemische Adhäsion und Abgabe von Fluorid, Bewertungen der klinischen
Anwendung. Die zweite Studie vom Kapitel 3 erforschte die Adhäsion von
Faserstiften, die in Wurzeldentin mit Zementen, die drei derzeit verfügbaren
adhäsiven Techniken benutzen, zementiert wurden. Es wurde angenommen,
dass die simplifizierten Self-Etch und selbst-adhäsiven Techniken so
wirksam wie die klinisch nachgewiesene Etch-and-Rinse Technik sind. Um
die Adhäsion von Faserstiften festzustellen, wurde den „Thin-Slice Push-out“
Test verwendet.
Im Kapitel 4 wurde eine Studie, die die Wichtigkeit der
Lichtdurchlässigkeit durch den Faserstift scharf umriß, dargestellt. Diese
Studie erforschte, ob die Lichtdurchlässigkeit durch den Faserstift das
adhäsive Potenzial und die mikromechanischen Eigenschaften eines
dualhärtenden Resin-Zementes, der für die Zementierung von Faserstiften
angewendet wurde, beeinflusst. Erstens wurden spektrophotometriche
Messungen gemacht, um die Lichtdurchlässigkeit in verschiedenen Teilen
und in der Spitze des Faserstiftes von zwei Faserstiften, die sich nach einer
visuellen Beobachtung in ihren Lichtdurchlässigkeiten beträchtlich
voneinander zu unterscheiden schienen, festzustellen. Die Messungen zeigten
keine Lichtdurchlässigkeit in einem der Faserstifte, dagegen sank die
Lichtstärke von dem koronalen bis zum apikalen Teil des anderen Faserstiftes
und sie erreichte den Höchstwert in der Spitze. Nach den Messungen wurde
es untersucht, ob die Art des Faserstiftes die Kontinuität der Resin-
Zement/Wurzeldentin bzw. Resin-Zement/Faserstift Schnittstelle beeinflusst,
wenn die anderen Variablen konstant bleiben. Außerdem wurde es
festgestellt, ob die Art des Faserstiftes den Elastizitätsmodul bzw. die Härte
des Zementes beeinflusst.
188
Die folgenden Schlussfolgerungen können aus der Bewertung der folgenden
Aspekte, die mit der Zementierung von Faserstiften korrelieren, -
Behandlung der Oberfläche des Faserstiftes, Art des Resin-Zementes und
Lichtdurchlässigkeit durch den Faserstift – gezogen werden:
1. Das Sandstrahlen kann die Microtensile-Verbundfestigkeit mit
Methacrylat-Faserstiften erhöhen, daher wird die Notwendigkeit
zusätzlicher „Chair-Side“ Behandlungen vermieden. Die reduzierte
Anzahl der klinischen Schritte kann das klinische Verfahren
simplifizieren.
2. Verglichen mit dem Adhäsiv allein, kann das Sandstrahlen gefolgt von der
Anwendung eines Adhäsives die sofortige Verbundfestigkeit mit
Epoxydharz-Faserstiften verbessern. Das „accelerated Water Aging“ kann
den Faserstift/Resin-Zement bzw. Faserstift/Flowable-Komposit
Verbindungen, die von einem hydrophilen Adhäsiv vermittelt werden,
schaden.
3. Die experimentelle industrielle Behandlung der Oberfläche des
Faserstiftes und die Anwendung eines Adhäsives erhöhen die
Verbundfestigkeit zwischen Faserstift und Resin-Zement. Die industrielle
Behandlung kann die Zementierung simplifizieren. Die Zementierung von
Epoxydharz-Faserstiften ohne Behandlung der Oberfläche des Faserstiftes
ist nicht zu empfehlen.
4. Die selbst-adhäsiven Zemente scheinen eine erfolgversprechende neue
Technik für die indirekten Restaurationen inklusiv die Zementierung von
Faserstiften zu sein. Trotzdem stützt sich die Mehrheit der Daten der
Literatur auf Studien, die nur einen der Zemente, die derzeit zur
Verfügung für die Zahnärzte stehen, erforschten. Es wäre noch wichtiger
das langfristige klinische Verhalten dieser Materialien festzustellen, bevor
189
allgemeine Hinweise für ihre Anwendung für die Zementierung von
Faserstiften zu geben.
5. Die 24 St. Push-out Verbundfestigkeit mit Faserstiften wurde von den
Zementen signifikant beeinflusst. Die Ergebnisse dieser Dissertation
ermöglichen nicht, eine der drei untersuchten adhäsiven Techniken mit
Sicherheit zu bevorzugen. Trotzdem zeigt die Self-Etching Technik unter
den ausgewählten experimentellen Bedingungen eine schlechtere
Adhäsion mit dem Wurzeldentin, verglichen mit den Etch-and-Rinse bzw.
Total-etch Techniken.
6. Verglichen mit der Zementierung von lichtdurchlässigen Faserstiften,
zeigte die Zementierung von lichtundurchlässigen Faserstiften mit einem
dualhärtenden Resin-Zement einen geringeren Prozentsatz von Kontinuität
der Resin-Zement/Wurzeldentin bzw. Resin-Zement/Faserstift
Schnittstellen.
7. Elastizitätsmodul und Vickershärte des Zementes sanken signifikant von
dem koronalen bis zum apikalen Drittel des Post-Space unabhängig von
der Lichtdurchlässigkeit des Faserstiftes. Trotzdem zeigte die
Zementierung von lichtdurchlässigen Faserstiften höhere Werte des
Elastizitätsmoduls und der Vickershärte des Zementes, verglichen mit der
Zementierung von lichtundurchlässigen Faserstiften.
Sažetak i zaklju�ci
Cilj ove teze bio je da ispita tri faktora cementiranja kompozitnih ko�i�a
oja�anih vlaknima: priprema površine ko�i�a, vrsta kompozitnog cementa za
cementiranje ko�i�a i svetlosna provodljivost ko�i�a. Radna hipoteza bila je
da ovi faktori mogu uticati na uspešnost cementiranja ko�i�a. Kako bi se ova
190
hipoteza proverila, sprovedeno je nekoliko laboratorijskih istraživanja. Tezu
�ine �etiri poglavlja u kojima je predstavljeno šest publikovanih radova.
Poglavlje 1 obuhvata uvod u osnovnu temu. Predstavljena je primena
kompozitnih ko�i�a u zbrinjavanju endodontski le�enih zuba. Diskutovano je
o osnovnim svojstvima kompozitnih ko�i�a, kao što su sastav, elasti�nost i
estetika, kao i o klini�kim pogodnostima koje ova svojstva pružaju. Opisane
su indikacije u kojima kompozitni ko�i�i mogu u potpunosti ispoljiti svoj
potencijal, uklju�uju�i i posebne prednosti koje primena ovih ko�i�a donosi u
de�joj stomatologiji i traumatologiji. Iako se svi kompozitni ko�i�i sastoje od
istih osnovnih komponenti, njihova mehani�ka svojstva i kvalitet u klini�kim
uslovima mogu zna�ajno da variraju u zavisnosti od proizvo�a�a. Zbog toga
su predstavljena neka od svojstava koja mogu da uti�u na izbor ko�i�a. Osim
tri faktora kojima se bavi ova teza, smatra se da još nekoliko drugih faktora
može uticati na uspešnost cementiranja ko�i�a. U Poglavlju 1 su ukratko
diskutovani slede�i: vrsta paste za definitivno punjenje kanala korena,
koli�ina preostalog kruni�nog dentina, preparacija ferula i debljina sloja
kompozitnog cementa.
Priprema površine ko�i�a i njen uticaj na adheziju izme�u ko�i�a i
kompozitnog cementa ispitivani su u tri rada predstavljena u Poglavlju 2. U
ovim radovima, nakon primene razli�itih na�ina pripreme površine ko�i�a,
ispitivana je ja�ina veze izme�u ko�i�a i cementa pomo�u testa otpornosti
mikrouzoraka na istezanje (“microtensile bond strength test”). Tako�e su
posmatrane površine tretiranih i netretiranih ko�i�a, kao i adhezivni spojevi
cement-ko�i� skening elektronskim mikroskopom (SEM). U prvom radu
ispitivan je uticaj peskiranja i razli�itih ordinacijskih postupaka pripreme
ko�i�a sa metakrilatnim matriksom na ja�inu veze sa dvostruko-
polimerizuju�im kompozitom. U drugom radu ispitivan je uticaj pripreme
ko�i�a sa matriksom od epoksi smole na ja�inu veze sa kompozitnim
191
cementom i te�nim kompozitom. Na sve ko�i�e bio je nanesen dvostruko-
polimerizuju�i adheziv, imaju�i u vidu da je ranije utvr�eno da ovakav
tretman efikasno pove�ava ja�inu veze kompozitnih materijala sa ko�i�ima
koji sadrže epoksi smolu. Rad je imao dva cilja: 1. utvrditi da li peskiranje pre
nanošenja adheziva uti�e na ja�inu veze ko�i�-cement i ko�i�-te�ni kompozit;
2. ispitati uticaj vode na vezu ko�i�-cement i ko�i�-te�ni kompozit koriste�i
model ubrzanog starenja materijala. U tre�em radu Poglavlja 2 cilj je bio da
se ispita uticaj eksperimentalne fabri�ke pripreme i razli�itih ordinacijskih
na�ina pripreme površine ko�i�a sa matriksom od epoksi smole na ja�inu
veze sa kompozitnim cementima. Eksperimentalnu fabri�ku pripremu �inilo
je dva koraka: nanošenje sloja cirkonijum oksida debljine 1�m, a zatim
silanizacija 3-(trimetoksilil) propil metakrilatom. Prema tvrdnji proizvo�a�a,
ovakvom pripremom obezbe�uje se mikromehani�ka retencija, kao i hemijska
veza izme�u silana i adheziva ili cementa. Ordinacijski postupci pripreme
ko�i�a koji su ispitivani u ovom radu obuhvatili su nanošenje silana i
nanošenje adheziva, dok u kontrolnoj grupi površina ko�i�a nije tretirana.
Mikroskopski su posmatrane površine tretiranih i netretiranih ko�i�a, kao i
adhezivni spojevi cement-ko�i� (SEM). Površina fabri�ki pripremljenih
ko�i�a tako�e je ispitivana pomo�u EDAX analize (Energy Dispersive
Analysis by X-ray) u skening elektronskom mikroskopu.
Tema Poglavlja 3 bili su kompozitni cementi i razli�iti adhezivni
pristupi koji se mogu koristiti pri cementiranju kompozitnih ko�i�a. Ovo
poglavlje �ine dva rada. Posebna pažnja posve�ena je samoadhezivnim
kompozitnim cementima, koji �ine najnoviju i najmanje ispitivanu kategoriju
kompozitnih cemenata. Prvi rad Poglavlja 3 je pregled literature �iji je cilj bio
da pruži informacije o samoadhezivnim kompozitnim cementima na osnovu
originalnih nau�nih radova objavljenih u recenziranim �asopisima koji su
indeksirani u bazi PubMed. Rezultati su klasifikovani u slede�e kategorije:
192
adhezija sa zubnim tkivima (gle�, dentin, dentin kanala korena), adhezija sa
restaurativnim materijalima (endodontski ko�i�i, keramika, titanijum),
marginalna adaptacija, mikropropustljivost, mehani�ka svojstva,
biokompatibilnost, hemijska adhezija i otpuštanje fluorida, ocena kvaliteta
tokom klini�ke upotrebe. U drugom radu Poglavlja 3 ispitivana je adhezija
kompozitnih ko�i�a cementiranih pomo�u tri aktuelna adhezivna pristupa.
Radna hipoteza bila je da su jednostavniji, samoadhezivni i samonagrizaju�i
pristup, jednako efektivni kao klini�ki potvr�en pristup potpunog nagrizanja.
Kako bi se ispitala adhezija ko�i�a merena je retencija pomo�u testa tankih
popre�nih preseka (thin-slice push-out test).
U Poglavlju 4 predstavljen je rad koji ispituje važnost svetlosne
provodljivosti ko�i�a. U ovom radu ispitivan je uticaj svetlosne provodljivosti
ko�i�a na adheziju dvostruko-polimerizuju�eg kompozitnog cementa, kao i na
mikromehani�ka svojstva cementa. Spektrofotometrijskim merenjima
utvr�ena je svetlosna provodljivost dva ko�i�a za koje je na osnovu vizuelnih
zapažanja pretpostavljeno da se u ovom svojstvu zna�ajno razlikuju. Merenja
su izvršena na razli�itim nivoima ko�i�a i na apikalnom vrhu. Utvr�eno je
odsustvo svetlosne provodljivosti kroz jedan od dva ko�i�a, dok je kroz drugi
intenzitet propuštene svetlosti opadao od koronarnog ka apikalnom nivou, a
na apikalnom vrhu dostizao najvišu vrednost. Nakon merenja, ispitivan je
uticaj tipa ko�i�a na kontinuitet adhezivnog spoja cement-dentin i cement-
ko�i�. Tako�e, ispitivan je uticaj tipa ko�i�a na modul elasti�nosti i tvrdo�u
cementa.
Na osnovu ispitivanja slede�ih faktora cementiranja kompozitnih ko�i�a:
priprema površine ko�i�a, tip kompozitnog cementa i svetlosna provodljivost
ko�i�a, mogu se izvesti slede�i zaklju�ci:
193
1. Peskiranje može da poboljša ja�inu veze kompozitnih materijala sa
metakrilatnim kompozitnim ko�i�ima i da eliminiše potrebu za dodatnim
ordinacijskim tretmanima površine ko�i�a. Smanjenje broja klini�kih
koraka doprinosi jednostavnosti klini�kih procedura.
2. Peskiranje pra�eno aplikacijom adheziva poboljšava ja�inu veze
kompozitnih materijala (cementa i te�nog kompozita) sa kompozitnim
ko�i�ima od epoksi smole, izmerenu neposredno nakon cementiranja
ko�i�a. Adhezivni spoj ko�i�a pripremljenih adhezivom sa kompozitnim
cementom i te�nim kompozitom može biti ugrožen ubrzanim starenjem u
vodi.
3. Eksperimentalna fabri�ka priprema i aplikacija adheziva poboljšavaju
ja�inu veze izme�u cementa i kompozitnog ko�i�a sa matriksom od epoksi
smole. Fabri�ki tretman može pojednostaviti klini�ki postupak
cementiranja. Cementiranje kompozitnih ko�i�a sa matriksom od epoksi
smole bez pripreme površine ko�i�a se ne preporu�uje.
4. Samoadhezivni kompozitni cementi mogli bi da ponude obe�avaju�i novi
pristup u indirektnim restaurativnim postupcima, uklju�uju�i cementiranje
kompozitnih ko�i�a. Me�utim, najve�i broj podataka iz literature o ovim
cementima poti�e iz laboratorijskih istraživanja samo jednog od više
cemenata koji su trenutno na raspolaganju klini�arima. Neophodne su
dugotrajne klini�ke studije kako bi se mogla dati generalna preporuka za
upotrebu samoadhezivnih cemenata u cementiranju ko�i�a.
5. Retencija kompozitnih ko�i�a merena nakon 24 sata od cementiranja
zna�ajno se razlikovala kod razli�itih kompozitnih cemenata. Na osnovu
rezultata ove teze nije mogu�e sa sigurnoš�u tvrditi da jedan od tri
adhezivna pristupa daje bolje rezultate u odnosu na ostala dva. Ipak,
metodom koji je koriš�en ustanovljena je lošija adhezija ko�i�a
194
koriš�enjem samonagrizaju�eg pristupa u odnosu na samoadhezivni i
pristup potpunog nagrizanja.
6. Procenat kontinualnog adhezivnog spoja cement-dentin i cement-ko�i� bio
je zna�ajno viši nakon cementiranja ko�i�a koji propušta svetlost u
pore�enju sa ko�i�em koji ne propušta svetlost.
7. Modulus elasti�nosti i tvrdo�a po Vikersu cementa zna�ajno su opadali od
koronarnog ka apikalnom nivou nezavisno od svetlosne provodljivosti
ko�i�a. Me�utim, modulus elasti�nosti i tvrdo�a po Vikersu bili su
zna�ajno viši nakon cementiranja ko�i�a sa svetlosnom provodljivoš�u u
odnosu na ko�i� koji ne provodi svetlost.
195
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Curriculum vitae
Dr. Ivana Radovic
Date of birth: April 9th, 1976
Place of birth: Belgrade, Serbia
Civil status: Married (former last name: Davitkov)
Citizenship: Serbian
Work address: Dr Subotica 11, 11000 Beograd, Serbia
Home address: Dr Agostina Neta 24, 11070 Novi Beograd, Serbia
Telephone number: +381 11 2684581
E-mail address: [email protected]
2001: Degree in Dentistry, Faculty of dentistry, University of Belgrade,
Serbia
Research activity
2004: Nova Southeastern University, Fort Lauderdale, Florida, USA
(conducting experiments within the scope of Master thesis).
2002 – 2005: Postgraduate studies at the Faculty of Dentistry, Belgrade,
Serbia. Master thesis “Bond strength, microleakage and SEM investigation of
self-etching adhesive systems” defended on September 27th 2005.
2006: Master of Science in Dental Materials and their clinical applications,
University of Siena.
219
Professional position
2002 – Teaching and research assistant, Clinic for pediatric and preventive
dentistry, Faculty of dentistry, University of Belgrade, Serbia.
Membership in Dental Societies
2002 - Serbian doctors’ society
2004 - International Organization for Dental Research (IADR)
2006 - Serbian Society of Pediatric and Preventive Dentists
2009 - European Academy of Paediatric Dentistry (EAPD)
International publications
Beloica M, Goracci C, Carvalho CAR, Radovic I, Margvelashvili M, Vulicevic ZR, Ferrari M (2010). Microtensile vs microshear bond strength of all-in-one adhesives to unground enamel. Journal of Adhesive Dentistry: In press
Beloica M, Carvalho CAR, Radovic I, Margelashvili M, Goracci C,
Vulicevic ZR, Ferrari M (2008). Efficacy of all-in-one adhesive systems on unground enamel. International Dentistry South Africa 10(5): 12-9.
Cagidiaco MC, Radovic I, Simonetti M, Tay F, Ferrari M (2007). Clinical performance of fiber post restorations in endodontically treated teeth: 2-year results. Int J Prosthodont 20(3): 293-8. Coniglio I, Magni E, Goracci C, Radovic I, Carvalho CA, Grandini S, Ferrari M (2008). Post space cleaning using a new nickel titanium endodontic drill combined with different cleaning regimens. J Endod 34(1): 83-6.
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Dall'oca S, Papacchini F, Radovic I, Polimeni A, Ferrari M (2008). Repair potential of a laboratory-processed nano-hybrid resin composite. J Oral Sci 50(4): 403-12. Ferrari M, Cagidiaco MC, Goracci C, Vichi A, Mason PN, Radovic I, Tay F (2007). Long-term retrospective study of the clinical performance of fiber posts. Am J Dent 20(5): 287-91. Magni E, Coniglio I, Radovic I, Goracci C, Ilie N, Hickel R, Cagidiaco MC (2009). Effect of diagnostic method and operator’s experience on the detection of occlusal caries in posterior permanent teeth: an in vivo pilot study. International Dentistry South Africa 11(1): 32-40. Magni E, Mazzitelli C, Papacchini F, Radovic I, Goracci C, Coniglio I, Ferrari M (2007). Adhesion between fiber posts and resin luting agents: a microtensile bond strength test and an SEM investigation following different treatments of the post surface. J Adhes Dent 9(2): 195-202. Magni E, Radovic I, Coniglio I, Papacchini F, Mazzitelli C, Ferrari M (2007). Bonding of self-etching adhesive/flowable composite combinations to enamel and dentin: a microtensile bond strength evaluation. . International Dentistry South Africa 9(4): 6-18. Mazzitelli C, Magni E, Radovic I, Papacchini F, Goracci C, Ferrari M (2007). The adhesion between FRC posts and resin core materials following different treatments of the post surface. . International Dentistry South Africa 9(2): 30-40. Monticelli F, Osorio R, Sadek FT, Radovic I, Toledano M, Ferrari M (2008). Surface treatments for improving bond strength to prefabricated fiber posts: a literature review. Oper Dent 33(3): 346-55. Papacchini F, Magni E, Radovic I, Mazzitelli C, Monticellia F, Goracci C, Polimeni A, Ferrari M (2007). Effect of intermediate agents and pre-heating of repairing resin on composite-repair bonds. Oper Dent 32(4): 363-71. Papacchini F, Monticelli F, Hasa I, Radovic I, Fabianelli A, Polimeni A, Ferrari M (2007). Effect of air-drying temperature on the effectiveness of silane primers and coupling blends in the repair of a microhybrid resin composite. J Adhes Dent 9(4): 391-7.
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Papacchini F, Monticelli F, Radovic I, Chieffi N, Goracci C, Tay FR, Polimeni A, Ferrari M (2007). The application of hydrogen peroxide in composite repair. J Biomed Mater Res B Appl Biomater. Papacchini F, Radovic I, Magni E, Goracci C, Monticelli F, Chieffi N, Polimeni A, Ferrari M (2008). Flowable composites as intermediate agents without adhesive application in resin composite repair. Am J Dent 21(1): 53-8. Papacchini F, Toledano M, Monticelli F, Osorio R, Radovic I, Polimeni A, Garcia-Godoy F, Ferrari M (2007). Hydrolytic stability of composite repair bond. Eur J Oral Sci 115(5): 417-24. Porciani PF, Vano M, Radovic I, Goracci C, Grandini S, Garcia-Godoy F, Ferrari M (2008). Fracture resistance of fiber posts: combinations of several small posts vs. standardized single post. Am J Dent 21(6): 373-6. Radovic I, Corciolani G, Magni E, Krstanovic G, Pavlovic V, Vulicevic ZR, Ferrari M (2009). Light transmission through fiber post: The effect on adhesion, elastic modulus and hardness of dual-cure resin cement. Dent Mater 25(7): 837-44. Radovic I, Mazzitelli C, Chieffi N, Ferrari M (2008). Evaluation of the adhesion of fiber posts cemented using different adhesive approaches. Eur J Oral Sci 116(6): 557-63. Radovic I, Monticelli F, Cury AH, Bertelli E, Vulicevic ZR, Ferrari M (2008). Coupling of composite resin cements to quartz fiber posts: a comparison of industrial and chairside treatments of the post surface. J Adhes Dent 10(1): 57-66. Radovic I, Monticelli F, Goracci C, Cury AH, Coniglio I, Vulicevic ZR, Garcia-Godoy F, Ferrari M (2007). The effect of sandblasting on adhesion of a dual-cured resin composite to methacrylic fiber posts: Microtensile bond strength and SEM evaluation. J Dent 35(6): 496-502. Radovic I, Monticelli F, Goracci C, Vulicevic ZR, Ferrari M (2008). Self-adhesive resin cements: a literature review. J Adhes Dent 10(4): 251-8. Radovic I, Monticelli F, Papacchini F, Magni E, Cury AH, Vulicevic ZR, Ferrari M (2007). Accelerated aging of adhesive-mediated fiber post-resin composite bonds: A modeling approach. J Dent 35(8): 683-9.
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Radovic I, Vulicevic ZR, Garcia-Godoy F (2006). Morphological evaluation of 2- and 1-step self-etching system interfaces with dentin. Oper Dent 31(6): 710-8. Simonetti M, Radovic I, Vano M, Chieffi N, Goracci C, Tognini F, Ferrari M (2006). The influence of operator variability on adhesive cementation of fiber posts. J Adhes Dent 8(6): 421-5. Vulicevic ZR, Radovic I, Cury AH, Krstanovic G, Mandic J, Ferrari M (2008). Microtensile bond strength of self-etching adhesives to dentin. Metalurgija – Journal of Metallurgy 14(2): 101-9. Zhang L, Magni E, Radovic I, Wang YJ, Chen JH, Ferrari M (2008). Effect of curing modes of dual-curing luting systems and root regions on retention of translucent fiber posts in root canals. J Adhes Dent 10(3): 219-26. Zhang L, Wang YJ, Radovic I, Chieffi N, Chen JH, Ferrari M (2006). Adhesion of two dual-cure core resins to silica fiber posts treated with different bonding agents. International Dentistry South Africa 8(6): 38-47. Abstracts 1. Radovic I, Mazzitelli C, Chieffi N, Ferrari M. Adhesion of fiber posts
cemented using different adhesive approaches. J Dent Res 87(Spec Iss B):(abstract no. 1750), 2008 (www.dentalresearch.org). 86th General Session and Exhibition of the International and Canadian Associations for Dental Research, July 2-5. 2008, Toronto, Canada. Poster presentation.
2. Radovic I, Monticelli F, Papacchini F, Magni E, Cury AH, Vulicevic ZR, Ferrari M. Accelerated aging of adhesive-mediated fiber post-resin composite bonds. J Dent Res 86(Spec Iss B):(abstract no. 0429), 2007 (www.dentalresearch.org). 42nd Annual Meeting IADR-Continental European and Israeli Divisions, September 26-29. 2007, Thessaloniki, Greece. Poster presentation.
3. Papacchini F, Ferrari M, Radovic I, Monticelli F, Toledano M, Osorio R, Garcia-Godoy F, Polimeni A. Effect of thermocycling on composite-to-composite adhesion. J Dent Res 86(Spec Iss B):(abstract no. 0303), 2007
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(www.dentalresearch.org). 42nd Annual Meeting IADR-Continental European and Israeli Divisions, September 26-29. 2007, Thessaloniki, Greece. Poster presentation.
4. Radovic I, Monticelli F, Cury AH, Bertelli E, Vulicevic ZR, Ferrari M. Comparison of Industrial and “Chair-Side” Treatments of Fiber Post Surface. J Dent Res 86(Spec Iss A):(abstract no. 1532), 2007 (www.dentalresearch.org). 85th General Session and Exhibition of the International, American and Canadian Associations for Dental Research, March 21-24. 2007, New Orleans, Louisiana, USA. Poster presentation.
5. Papacchini F, Monticelli F, Radovic I, Polimeni A, Ferrari M. Influenza dell’agente intermedio sulla stabilità idrolitica dell’adesione composito-composito (Effect of the intermediate agent on the hydrolytic stability of the composite-repair bond). XI National Congress SIDOC (Società Italiana di Odontoiatria Conservatrice) "Adesione, estetica e funzione", February 15-17. 2007, Rome, Italy. Poster presentation.
6. Cury AH, Radovic I, Goracci C, Chieffi N, Ferrari M. Strategies to lute
fiber post: immediate and 1week push-out retention. Academy of Dental Materials Meeting 2006, October 23-25. 2006, Sao Paulo, Brazil. Poster presentation.
7. Papacchini F, Radovic I, Magni E, Monticelli F, Goracci C, Chieffi N,
Ferrari M. The effect of intermediate agents in composite repair bond strength. J Dent Res 85(Spec Iss C):(abstract no. 0308), 2006 (www.dentalresearch.org). IADR Pan European Federation 2006, September 13-16. 2006, Dublin, Ireland. Poster presentation.
8. Radovic I, Monticelli F, Cury AH, Goracci C, Cantoro A, Coniglio I,
Ferrari M. Surface treatment influence on fiber post - resin cement bond strength. J Dent Res 85(Spec Iss C):(abstract no. 0245), 2006 (www.dentalresearch.org). IADR Pan European Federation 2006, September 13-16. 2006, Dublin, Ireland. Oral presentation.
9. Radovic I, Cury AH, Vulicevic ZR, Garcia-Godoy F, Ferrari M.
Microtensile bond strength of two- and one-step self-etching systems to dentin. The Third CONSEURO 2006 on Across European Borders Prevention, Restorations and Esthetics, February 9-11. 2006, Rome, Italy. Poster presentation.
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10. Davitkov I, Vulicevic ZR, Garcia-Godoy F. The influence of flowable composite as an initial layer on microleakage of self-etching systems. 10th Congress of the Balkan Stomatological Society, May 12-14. 2005, Belgrade, Serbia and Montenegro. Oral presentation.
11. Davitkov I, Vulicevic ZR, Garcia-Godoy F. SEM investigation of different self-etching systems interface with dentin. J Dent Res 84(Spec Iss A):(abstract no. 0158), 2005 (www.dentalresearch.org). 83rd General Session and Exhibition of the International, American and Canadian Associations for Dental Research, March 9-12. 2005, Baltimore, Maryland, USA. Oral presentation.
12. Davitkov I, Vulicevic ZR. SEM investigation of self-etching primers
influence on unground and ground enamel. 4th Congress of Serbia and Montenegro dentists, October 13-16. 2004, Herceg Novi, Serbia and Montenegro. Poster presentation.
13. Davitkov I, Vulicevic ZR. Microleakage of a total-etch and a self-etch
bonding system under composite resins with various filler content. 7th Congress of the European Academy of Pediatric Dentistry, Jun 10-13. 2004, Barcelona, Spain. Oral presentation.
14. Davitkov I, Vulicevic ZR. Microleakage of three different self-etching
adhesive systems. 9th Congress of the Balkan Stomatological Society, May 13-16. 2004, Ohrid, Macedonia. Oral presentation.
15. Vulicevic ZR, Todorovic A, Davitkov I. Adhesive bridges as space
maintainers. First International Congress of Serbia and Montenegro Orthodontists, October 2-5. 2003, Belgrade, Serbia and Montenegro. Poster presentation.
16. Beloica D, Vulicevic ZR, Davitkov I. FRC Postec in pediatric dentistry.
8th Congress of the Balkan Stomatological Society, May 2003, Tirana, Albania. Poster presentation.
17. Vulicevic ZR, Davitkov I, Todorovic A, Spadijer A. Ribbond reinforced
Class II composite fillings – a case report. 7th Congress of the Balkan Stomatological Society, March 28-30. 2002, Cushadasi, Turkey. Poster presentation.
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18. Vulicevic ZR, Todorovic A, Davitkov I. Occlusal reconstruction with prefabricated ceramic inlays. 8th Symposium of Serbia prosthetitians, Jun 22-23. 2001, Zlatibor, Yugoslavia. Poster presentation.
19. Davitkov I (author), Vulicevic ZR (mentor). Ribbond reinforced composite bridges. 42nd Congress of medicine and dentistry students of Yugoslavia, April 17-21. 2001, Lepenski Vir, Yugoslavia. Oral presentation.
20. Vulicevic ZR, Davitkov I. Composite-compomer sandwich technique
(case report). 3rd Congress of Yugoslavia dentists, September 20-23. 2000, Novi Sad, Yugoslavia. Poster presentation.
21. Davitkov I (author), Vulicevic ZR (mentor). The use of compomers in
pediatric dentistry. 41st Congress of medicine and dentistry students of Yugoslavia, April 25-29. 2000, Zlatibor, Yugoslavia. Oral presentation.
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Acknowledgements
This thesis is respectfully submitted to Prof. Silvano Focardi, Rector of the University of Siena, to Prof. Gian Maria Rossolini, Dean of the Faculty of Medicine of the University of Siena, to Prof. Marco Ferrari, Director of the Department of Dental Science, Dean of School of Dental Medicine, Director of the PhD Program in “Biotechnologies: section of Dental Biomaterials”, University of Siena.
It is also submitted to Prof. Branko Kova�evi�, Rector of the University of Belgrade and to Prof. Dragoslav Stamenkovi�, Dean of the Faculty of Dentistry, University of Belgrade. The Siena PhD program has been one of the greatest adventures and experiences in my life. Having the possibility to take this journey and encounter numerous wonderful people on the way made me feel as a truly rich person. The quality of Siena PhD programme that I appreciated and enjoyed the most was the opportunity to work in a team. This thesis is a result of a joint effort. It would never have become reality without the generous help of my professors and a large supportive network of colleagues and friends. Even though I don’t have the possibility to mention everyone by name, I truly cherish each contribution. I am heartily thankful to my Promoter, Prof. Marco Ferrari, whose encouragement, guidance and clear broad vision have been the continuous source of positive energy and motivation for me. He has always been a strong and supportive advisor to me throughout the program, and at the same time he encouraged me to pursue and implement independent ideas. My Co-Promoter, Prof. Zoran Vuli�evi�, introduced me to the world of science almost 10 years ago. Since then, he has been providing me with various opportunities and challenges in the academic world which have boosted my confidence. I am deeply grateful for his guidance and advice I know I can always count on. I would also like to express gratitude to my committee members for time and attention they put in reviewing my thesis. Prof. Francesca Monticelli taught me how to expand my views and how to build a solid research protocol and put it in clear and concise written form. I am grateful to her for experience and knowledge that she generously shared with me, both in laboratory work and in writing papers.
Prof. Cecilia Goracci introduced the world of statistics to me patiently and clearly. This made all the time I spent in front of seemingly endless data on SPSS screen a stimulating challenge I truly enjoyed and was happy to take.
Dr. Federica Papacchini and Dr. Alvaro Cury welcomed me the first time I visited Siena. Besides providing all the help I needed in the lab, they also made my first stay a joyful memory I often go back to. Throughout the entire time I spent in Siena we shared many hours working and laughing together as colleagues and friends.
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Dr. Elisa Magni helped me many times with clear reasoning and a fast constructive approach when it was needed the most. I am also grateful to Elisa for the hospitality she generously showed during my visits to her beautiful city. It is a pleasure to thank many dear PhD colleagues who have made significant contributions and invested their time, ideas and energy into improving my work: especially Dr. Claudia Mazzitelli, Dr. Gabrielle Corciolani and Dr. Nicoletta Chieffi. I gratefully acknowledge the translations of Summary and conclusions that were made by Dr. Federica Papacchini (Italian) and Dr. Elisa Magni (German). A unique part of Siena living experience had been the stay in Santa Chiara College for PhD students. I thank all the friends I met there for happy times we spent together in small everyday joys of College life and in numerous field trips around Toscana. I owe an exceptional dept to the “Serbian side” of my PhD road. Firstly, to all the Professors and colleagues from the Clinic for pediatric and preventive dentistry. I am deeply grateful for the kind support they showed during the year I spent in Siena, as well as during several shorter leaves of absence that I had to take in order to complete the program. I especially appreciated the instantly positive attitude and confidence in me that the late Prof. Marko Vulovi�, former Clinic director, expressed in the early stages of preparation to apply for the program. I thank the Clinic director, Prof. Mirjana Ivanovi�, for her warmth and for always having time to share caring and encouraging words. Prof. Vuli�evi�’s, Prof. Vulovi�’s and Prof. Ivanovi�’s supportive presence during my Master thesis defence in Siena in December 2006 had a great impact on my self-esteem and created an especially valued page in the book of my Siena memories. Special thanks go to Professor Dragoslav Stamenkovi�, the Dean of the Faculty of dentistry. I appreciate his catching enthusiasm, positive energy and the trust he has been showing me.
I am grateful to Professor Vladimir Pavlovi� for his assistance with Scanning Electron Microscope, as well as for the time we spent in discussions of our findings. I also thank Dr. Goranka Krstanovi�, a very dear friend and colleague, for her precious help that was very important and significant for me in the final stages of this project.
Architect Milan Stefanovi�, my brother in law and a dear friend, made beautiful 3-D schemes and drawings that considerably enhanced the way this thesis is reported. I truly appreciate the time he spent doing this, as well as his infinite kindness and patience.
My sister Nevena and my parents have always been there for me with unconditional love, support and encouragement. My overwhelming feeling of awareness of being blessed with such a family only begins to explain how much I am grateful to them.
I deeply thank my love, Marko, for his patience, sacrifice, understanding, for having faith in me and being proud of me, for listening to my problems and for gladly taking part in resolving them countless times. I thank him for being so perceptive to my dreams and wishes and for enabling me to live them.