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8/10/2019 Effect of Solvent Evaporation Strategies On
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Effect of solvent evaporation strategies on
regional bond strength of one-step self-etch
adhesives to root canal dentine
S. Thitthaweerat1,2,3, M. Nakajima1, R. M. Foxton4 & J. Tagami1,3
1Cariology and Operative Dentistry, Department of Oral Health Sciences, Tokyo Medical and Dental University, Tokyo, Japan;2Department of Operative Dentistry and Endodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand; 3Global
Center Excellence (GCOE) Program, International Research Center for Molecular Science in Tooth and Bone Diseases, Tokyo
Medical and Dental University, Tokyo, Japan; and 4Division of Conservative Dentistry, Kings College London Dental Institute
at Guys, Kings and St Thomas Hospitals, Kings College London, London, UK
Abstract
Thitthaweerat S, Nakajima M, Foxton RM, Tagami
J. Effect of solvent evaporation strategies on regional bond
strength of one-step self-etch adhesives to root canal dentine.
International Endodontic Journal, 46, 10231031, 2013.
Aim To evaluate the efficacy of different solvent
evaporation strategies on bonding of one-step self-etch
adhesives to root canal dentine.
Methodology Two dual-cure resin core systems
(Clearfil DC Bond/Clearfil DC Core Automix and Clear-
fil Tri-S Bond Plus/Clearfil DC Core Plus; Kuraray
Noritake Dental, Tokyo, Japan) were equally applied
in 24 post spaces from extracted human mandibular
premolars. After the adhesive application, specimens
were randomly assigned into four water/solvent evap-
oration strategies as follows (I) insertion of absorbent
paper point for 10 s: P, (II) 10 s air-blowing: A, (III)
as (II) followed by insertion of absorbent paper point:
AP, (IV) as (III) followed by 10 s additional air-
blowing: APA. Then, the adhesives were light cured,
and resin core materials were placed into the post
space, followed by light curing for 60 s. After water
storage for 24 h, 0.6 9 0.6 mm-thick beams were
prepared to measure the regional lTBS. The mode of
failure was also observed. The lTBS values were
statistically analysed using three-way ANOVA andDuncan HSD test (a = 0.05).
Results In the coronal region, there were no signifi-
cant differences in lTBS between each evaporation
strategy (P > 0.05), except P group. However, in the
apical region, APA and AP groups significantly increased
in lTBS compared with A and P groups (P < 0.05).
Only in the APA group of Clearfil Tri-S Bond Plus/
Clearfil DC Core Plus, was there no significant differ-
ence in lTBS between the coronal and apical regions
(P > 0.05).
Conclusion The use of paper points with additional
air-blowing for removing excessive adhesive and
evaporating residual water/solvent would be effective
in producing higher bond strength for the tested one-
step self-etch adhesives and fewer blister formations
in deeper regions of the post space.
Keywords: bonding, micro-tensile bond strength,
one-step self-etch adhesive, root canal dentine, solvent
evaporation.
Received 20 November 2012; accepted 18 February 2013
Introduction
Generally, one-step self-etch adhesives are a mixture
of hydrophilic and hydrophobic resin monomers,
dissolved in water and organic solvents, such as
ethanol, acetone etc. The organic solvents improve the
miscibility of hydrophilic and hydrophobic compo-
nents and the diffusion of monomer into the hydrated
Correspondence: Masatoshi Nakajima, Cariology and Opera-
tive Dentistry, Department of Oral Health Sciences, Tokyo
Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku,
Tokyo 113-8549, Japan (Tel.: +81(0)3 5803 5483; fax:
+81(0)3 5803 0195; e-mail: nakajima.ope@tmd.ac.jp).
2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 10231031, 2013
doi:10.1111/iej.12093
1023
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demineralized matrix. Meanwhile, they play an impor-
tant role in removal of water from the adhesive sur-
face due to azeotropic dehydration (Van Landuyt et al.
2007, Loguercio et al. 2009). Air-drying after adhe-
sive application can facilitate the evaporation of
water/solvent from the applied dentine substrate
(Spreafico et al. 2006) and thin the adhesive layer,leading to diminishing amounts of water/solvent in
the adhesive layer (Zheng et al. 2001). However, com-
plete water/solvent evaporation is difficult to achieve
in the clinical situation because the air-blowing proce-
dure is restricted in the oral environment (Ikeda et al.
2005). Many studies have demonstrated that residual
water and solvent can dilute the monomer and inhibit
the polymerization reaction, resulting in a reduction of
bond strength (Galan et al. 1991, De Munck et al.
2005). Moreover, blister formation and higher perme-
ability of the adhesive layer would occur, leading to a
reduction in the quality of adhesive interface (Hashim-
otoet al. 2005, Ferrari et al. 2008).
To improve the bonding performance of one-step
self-etch adhesives, many studies have investigated
solvent evaporation strategies using flat coronal den-
tine surfaces, such as using warm air stream (Galan
et al. 1991, Klein-Junior et al. 2008, Garcia et al.
2009, Reis et al. 2010), extending the air-drying time
(Furuse et al. 2008, Giannini et al. 2008, Ikeda et al.
2008, Garcia et al. 2009) and increasing the air-
pressure (El-Askary & Van Noort 2011). However, it
has been indicated that these evaporation strategies
were not enough to completely remove residual
water/solvent from the adhesive layer (De Muncket al. 2005, Hashimoto et al. 2006).
Unlike coronal flat dentine surfaces, the root canal
dentine cavity appears to be a challenging bonding
substrate due to various factors, such as attenuation
of the light energy in the deeper region (Foxton et al.
2003, Aksornmuang et al. 2006, 2009, Mao et al.
2011) and limited accessibility to the root canal post
for bonding application and/or solvent evaporation
(Schwartz 2006, Breschi et al. 2009), which could
adversely affect the adhesive performance to root
canal dentine. Moreover, due to the narrower orifice
of the post cavity and/or further distance from the
air-blowing source to deeper region, efficient water/
solvent evaporation would deteriorate in the deeper
region. Spreading of the adhesive by air-blowing
would contribute to better solvent evaporation of the
adhesives and more polymerization (Galan et al.
1991). El-Askary & Van Noort (2011) have men-
tioned that increasing the distance from the dentine
substrate during air-drying significantly decreases
solvent evaporation from one-step self-etch adhesives,
reducing their bond strength. Therefore, the water/
solvent evaporation strategy prior to light curing is
very important for bonding to root canal dentine.
A previous study (Souza et al. 2007) reported that
using a paper point was useful for removing excessadhesive in root canal, leading to an improvement in
the bond strength to bovine root dentine. However,
there was a little information on which is the most
effective water/solvent evaporation strategy for bond-
ing a one-step self-etch adhesive to human root canal
dentine.
Therefore, the aim of this study was to determine
the effectiveness of different solvent evaporation strat-
egies in improving adhesion to human root canal
dentine. The null hypothesis was that applying differ-
ent solvent evaporation strategies had no effect on
the bond strength of one-step self-etch adhesives to
human root canal dentine.
Materials and methods
Preparation of bonded specimens
Twenty-four single-rooted human mandibular premo-
lar teeth extracted from adolescents for orthodontic
reasons, with similar root length and free of cracks,
caries and fractures, were collected following ethnical
approval by the Ethics Committee of Tokyo Medical
and Dental University under protocol No. 725 and
stored in refrigerated distilled water at 4 C beforebeing used. The crown was sectioned 2 mm above the
cementoenamel junction using a low-speed diamond
saw (Isomet; Buehler, Lake Bluff, IL, USA) with water
lubrication. The root canals were mechanically
enlarged using endodontic K-files with distilled water
irrigation until a size 25 file reached the canal
terminus. Then, post spaces were prepared using
Gates-Glidden drills (Matsutani Seisakusho Co. Ltd.,
Takanezawa, Japan) and FiberKor drills (Pentron
Corp., Wallingford, CT, USA) in a low-speed handpiece
under copious water-cooling to a depth of 8 mm from
the sectioned root surface and a diameter of 1.5 mm
at the apical end. Prior to the bonding procedure, the
external surfaces of the roots were built up with a
resin composite (Clearfil Majesty and Clearfil SE bond;
Kuraray Noritake Dental, Tokyo, Japan) to make grips
for testing and to prevent the external curing light,
which could pass through thin portions of the dentine
wall to the adhesive resin during photo-irradiation.
Solvent evaporation on bonding to root canal dentine Thitthaweerat et al.
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Two dual-cure resin core systems (Clearfil DC
Bond/Clearfil DC Core Automix, Clearfil Tri-S Bond
Plus/Clearfil DC Core Plus; Kuraray Noritake Dental,
Tokyo, Japan) were used. Each resin core system con-
sists of a one-step self-etching adhesive and a resin
core material, which the manufacturer suggests
should be used together. The chemical compositionsand bonding procedure of the materials are presented
in Table 1. After applying the adhesives to the walls
of the post spaces using a micro-brush disposable
applicator (Pentron Clinical Technologies), the post
spaces were randomly divided into four groups
according to the solvent evaporation technique, each
consisting of three teeth: Group 1(P): insertion of a
size 60 absorbent paper point (Dentsply Tulsa Dental,
Tulsa, OK, USA) for 10 s into the root canal; Group 2
(A): air-blowing for 10 s; Group 3(AP): Group 2
followed by insertion of an absorbent paper point for
10 s; Group 4 (APA): Group 3 followed by additive
air-blowing for 10 s. Air-blowing the adhesives was
performed using a dental triple syringe from 1 cm
above post orifice, whose air-pressure was approxi-
mately 3.5 kg cm2.
Then, all the adhesives were light cured in accor-
dance with the manufacturers instructions using a
halogen light source (Optilux 501; Demetron Kerr,
Danbury, CA, USA), whose mean light intensity was
550 mW cm2. For Clearfil DC Bond, the manufac-
turers instructions recommend 20 s light curing time
to adhesive, while Clearfil Tri-s Bond Plus is recom-
mended 10 s light curing time. Afterward, all the post
spaces were filled with dual-cure resin core material
using a guide tip ( 1.1 mm.) and light cured for 60 s.
Bond strength testing
After 24 h water storage at 37 C, each bonded speci-
men was sectioned perpendicular to the bonded inter-face using a low-speed diamond saw (Isomet) under
water-cooling to create 8, 0.6-mm-thick slabs. Four
coronal slabs were considered to represent the coronal
portion of the post space corresponding to the coronal
third of root canal, while those of four apical slabs
were considered to represent the apical region
corresponding to the middle third of root canal. Then,
each slab was cut transversely at the central part
of post space in mesio-distal direction to produce
0.6 9 0.6 mm-thick beam (Aksornmuang et al.
2009). One of the two interfaces of each beam was
randomly selected for lTBS testing. The ends of the
beam and the remaining interface were carefully
attached onto a testing device in universal testing
machine (EZ Test; Shimadzu, Kyoto, Japan) using cya-
noacrylate glue (Zapit; Dental Ventures of America,
Anaheim, CA, USA) and subjected to a tensile force at
a crosshead speed of 1 mm min1. After the speci-
mens were fractured, the cross-sectional area of each
beam was measured with digital calipers (Mitutoyo
CD15; Mitutoyo Co., Kawasaki, Japan) to 0.01 mm
accuracy, which was approximately 0.37 mm2. The
value was recorded in kilogram9force (kgf) and trans-
formed to lTBS value in MPa.
Table 1 The chemical compositions and bonding procedure of the materials used in this study
Materials Chemical compositions Bonding procedure
Clearfil DC Core Automix
(Kuraray Noritake Dental;
Tokyo, Japan)
Adhesive(Clearfil DC Bond)
A: 10-MDP, HEMA, Bis-GMA, colloidal silica, CQ, BPO
B: ethanol, water
Resin core material (Clearfil DC Core Automix)
Bis-GMA, TEGDMA, Hydrophobic aromatic dimethacrylate,
silanated barium glass filler, silanated silica, CQ, BPO, accelerators
Apply a mixture of liquid
A&B and leave for 20 s,
strong air blow for 10 s,
Light cured for 20 s
Clearfil DC Core Plus
(Kuraray Noritake Dental;
Tokyo, Japan)
Adhesive(Clearfil Tri-S Bond Plus)
10-MDP, HEMA, Bis-GMA, hydrophilic aliphatic dimethacrylate,
hydrophobic aliphatic methacrylate, colloidal silica, CQ, NaF,
accelerators, initiators, ethanol, water
Resin core material (Clearfil DC Core Plus)
Bis-GMA, TEGDMA, hydrophobic/hydrophilic aliphatic
dimethacrylate, hydrophobic aromatic dimethacrylate, silanated
barium glass filler, silanated colloidal silica, colloidal silica,
aluminum oxide filler, CQ, accelerator, initiator
Apply and leave for 10 s,
mild air blowing for more
than 5 s, light-curing for 10 s
10-MDP, 10-Methacryloyloxydecyl dihydrogen phosphate; HEMA, 2-hydroxyethyl methacrylate; Bis-GMA, 2,2-bis[4-(2-hydroxy-3-
methacryloyloxypropoxy)phenyl]propane; CQ, Camphorquinone; BPO, Benzoyl peroxide; TEGDMA, Triethylene glycol dimethacry-
late.
Thitthaweerat et al. Solvent evaporation on bonding to root canal dentine
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Fracture analysis
After testing, both the resin and dentine sides of the
fractured beams were mounted on brass tablets and
gold sputter-coated. Fracture surfaces were observed
using a scanning electron microscope (JSM-5310;
JEOL, Tokyo, Japan) at magnifications of 150 and500. The failure mode was classified as one of the fol-
lowing: adhesive failure, cohesive failure in resin,
cohesive failure in dentine and mixed adhesive. To
observe the presence of blister formation in each root
canal region within the adhesive layer, adhesive fail-
ure areas in the fractured beams were observed using
SEM at the magnification of 500.
Statistical analysis
Three-way ANOVA was performed to evaluate interac-
tions among the three variables (material tested, sol-
vent evaporation strategy, root region), and the
Duncan post hoc test was used for multiple compari-
sons (a = 0.05). The failure mode data were analysed
using the chi-squared test. All statistical analyses
were performed using SPSS software version 17 (SPSS
Inc., Chicago, IL, USA).
Results
The means and standard deviations of the regional
microtensile bond strengths of the materials and evap-
oration strategies are illustrated in Table 2. Three-
way ANOVA revealed that material tested, solvent evap-oration strategy and root region significantly affected
the lTBS to root canal dentine (P = 0.002,
P < 0.0001 and P < 0.0001, respectively). Significant
interactions between evaporation technique and root
region, material tested and root region were observed
(P = 0.01, P = 0.024, respectively).
For both regions of post space, the P group was
significantly lower lTBS than the other evaporation
strategies (P < 0.05). In the coronal region, the lTBS
of both materials were not significantly different
between the A, APand APA groups (P > 0.05); how-ever, in the apical region, Clearfil DC Core Plus
showed significant differences in the lTBS between
them (P < 0.05), in which the APA group exhibited
the highest bond strength. For Clearfil DC Core Auto-
mix, the AP and APA groups exhibited significantly
higher lTBS compared to the A group (P < 0.05).
Only for the APA group of Clearfil DC Core Plus, was
there no significant difference in lTBS between the
coronal and apical regions (P > 0.05), whereas for
the other experimental groups, the coronal region
were significantly higher lTBS than that of the apical
region (P < 0.05).
There was no pretesting failure during specimen
preparation. Figure 1 presents the failure mode per-
centage of the debonded specimens. In this study,
there was no failure within the dentine substrate.
The predominant failure modes occurred at the
adhesive interface between dentine and adhesive
resin. Chi-square testing revealed significant differ-
ences in failure mode between solvent evaporation
techniques in the apical region of the post space
(P < 0.05). The high incidence of cohesive failure in
resin was found in the A and P groups (41.7% and
33.3% for Clearfil DC Core Automix, respectively;
33.3% and 41.7% for Clearfil DC Core Plus, respec-tively). On the other hand, a notably lower number
of cohesive failures in resin were found in the APA
group (16.7% for Clearfil DC Core Automix, 8.3% for
Clearfil DC Core Plus).
Table 2 The lTBS to root canal dentin in each resin core system, evaporation technique and root region. There were signifi-
cant differences in lTBS between coronal and apical region, except in APAgroup of Clearfil DC Core Plus (P > 0.05).
Materials
Root regions
(n = 12 )
Solvent evaporation technique
P A AP APA
Clearfil DC Core Automix Coronal 28.01 3.971A 38.39 4.282A 38.40 3.422A 38.73 3.502A
P < 0.05 P < 0.05 P < 0.05 P < 0.05
Apical 20.78 2.871a 26.79 3.612a 30.86 3.333a 31.56 3.843a
Clearfil DC Core Plus Coronal 29.15 3.081A 38.43 4.232A 38.72 3.482A 39.00 3.842A
P < 0.05 P < 0.05 P < 0.05 NS
Apical 24.21 2.941b 28.52 4.172a 32.05 3.973a 36.53 3.434b
The same superscript number indicates no significant differences in lTBS for each row, while the same superscript capital and
small letter indicates no significant differences within each column at coronal and apical region ( P > 0.05).
P, paper point; A, air blow; AP, air blow+ paper point; APA, air blow+ paper point+ air blow.
Solvent evaporation on bonding to root canal dentine Thitthaweerat et al.
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The SEM micrographs of the adhesive and/or mixed
failure in the apical region of each material are presented
in Fig. 2, which show different amounts and sizes of
blisters within the adhesive layer in each experimental
group. Numerous blisters and large blisters were
observed in Clearfil DC Core Automix. On the other
hand, for Clearfil DC Core Plus, few blisters formed and
small blisters were found. Regarding the solvent evapo-
ration strategy, the APA group produced less blister
formation than the other experimental groups.
Discussion
Clinically, the placement of a post is critical for the
restoration of root filled teeth (Schwartz & Robbins
2004). However, post placement was not performed
in this study because the focus was on evaluating the
bonding performance of one-step self-etch adhesives
to root canal dentine. Aksornmuang et al. (2011)
recently reported that post placement decreased the
bond strength due to the increase of C-factor and
increased the number of pretesting failure specimen
comparing with no post placement.
Push-out tests and microtensile tests have been used
for the assessment of bonding to root canal dentine.
Push-out tests are useful to evaluate the retention of
posts luted in root canals (Van Meerbeek et al. 2010),
but the measured value includes a friction effect as well
as the bonding effect (Goracci et al.2005, Faria-e-Silva
et al. 2008). On the other hand, microtensile tests can
accurately measure the bond strength between resin
and dentine or post and resin (Bouillaguet et al. 2003,
Aksornmuanget al. 2011). However, sometimes there
are pretesting failures of specimens during specimen
preparation, which makes it difficult to investigate the
bonding performance (Goracci et al. 2004). In this
study, there were no pretesting failures. Therefore, in
this study, bonding efficacy between resin and dentine
could be evaluated.
For both materials used in this study, the apical
region exhibited lower lTBS than the coronal region.These results can be attributed to attenuation of the
light energy in deeper regions of the post space due to
increasing distance from the light source (Le Bell et al.
2003, Wu et al. 2009, Beriat et al. 2012). Previous
studies have demonstrated that the reduced light
energy in deeper regions reduced the bond strength of
dual-cure one-step self-etch adhesives in the apical
region because of incomplete polymerization of the
adhesive (Foxton et al. 2003, Aksornmuang et al.
2009), and it was suggested that extending the light
irradiation time and/or using a higher light-output
power unit can increase the bond strength to the apical
region by increasing the degree of polymerization of the
adhesive. Insufficient light energy would be one of the
factors responsible for a reduction in the bond strength
values of the one-step self-etch adhesives in the deeper
region. Furthermore, the occurrence of tubular sclero-
sis in the root canal may be the other factor affecting
the lower bond strength in the apical region of a post
Figure 1 The percentages of failure modes for each root region in different evaporation techniques. There were significant
differences in failure mode among different evaporation techniques at the apical regions in both materials.
Thitthaweerat et al. Solvent evaporation on bonding to root canal dentine
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space. Tubular sclerosis is the physiological deposition
of increasing amounts of peritubular dentine, which
increases from the apex towards the coronal direction
with age and is more prominent in mesial and distal
root aspects (Vasiliadis et al. 1983, Paqueet al. 2006).
Some studies have demonstrated that the obliteration
of dentinal tubules and the hypermineralized surface
layer is more resistant to demineralization by acidic
monomer than normal dentine (Tay & Pashley 2004,
Lopeset al.2011), preventing optimal resin infiltration
(a)
(b)
(c)
(d)
Figure 2 Representative SEM micrographs of the adhesive and/or mixed failure among solvent evaporation strategies at the
apical region of post space in Clearfil DC Core Automix (left) and Clearfil DC Core Plus (right); a) The paper point application
only [P]; b) The air-blowing only [A]; c) The use of paper point without additional air-blowing [AP]; d) The use of paper point
with additional air-blowing technique [APA]. Numerous blisters formation could be found when the adhesive was air blown
solely and only the paper point was used, while the use of paper point with additional air-blowing produced few blister forma-
tion within adhesive layer. The smaller size of blister formation was found in Clearfil DC Core Plus comparing to Clearfil DC
Core Automix.
Solvent evaporation on bonding to root canal dentine Thitthaweerat et al.
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into the dentinal tubules and subsequently lowering
the apical bond strength.
In the present study, the solvent evaporation strate-
gies except use of the absorbent paper point only
significantly affected the bond strength in the apical
region, but did not exert an affect at the coronal
region. Therefore, the null hypothesis that solventevaporation strategies did not affect the regional bond
strength to root canal dentine was partially rejected.
For water/solvent containing adhesives, water and solvents
should be completely eliminated from the adhesive
layer prior to light curing, because any residual
water/solvent may have an adverse effect on polymeri-
zation of the adhesive layer (Jacobsen & Soderholm
1995, Carvalho et al. 2003, Reis et al. 2003). Never-
theless, in the root canal, water/solvent evaporation
would be limited because of its configuration. Even
when using flat dentine surfaces, increasing the air-
blowing distance and reducing air-pressure caused a
reduction in the bond strength of one-step self-etch
adhesive (El-Askary & Van Noort 2011). Reducing the
air-pressure at the deeper region in the root canal
would cause further insufficient water/solvent evapo-
ration, resulting in a reduction in bond strength in the
apical region. These speculations are supported by the
failure modes in this study, in which there were a
large number of cohesive failures in resin, and numer-
ous blister formations were observed within the adhe-
sive layer (Fig. 2). Excess water/solvent may dilute the
concentration of co-monomer in the hybrid layer
(Galan et al. 1991, Hashimoto et al. 2005) and con-
tribute to the growth of non-uniformity in the adhe-sive layer, resulting in a reduction in bond strength
(Cho & Dickens 2004). Residual water/solvent within
the adhesive layer would be another responsible factor
for the reduction in bond strength values of the one-
step self-etch adhesives in the deeper regions.
In addition, the narrow and deep configuration of
the root canal would also cause the pooling of excess
adhesive in the apical region. The thick adhesive layer
pooled at the apical region in the root canal would
contain higher amounts of water/solvent, which
would increase the difficulty of solvent/water evapora-
tion (Zhenget al. 2001, De Munck et al. 2007). In this
study, additional usage of the paper point after air-
blowing significantly increased the bond strength in
the apical region compared with only air-blowing and
using the paper point solely. Souza et al. (2007) also
demonstrated that the use of a paper point after air-
blowing the adhesive could improve the bond strength
to bovine root canal dentine. These results would indi-
cate that only air-blowing the adhesive was not
enough to evaporate water/solvent from the adhesive
layer at the apical region. The paper point application
could minimize pooling of the adhesive layer at the api-
cal region, facilitating further residual solvent/water
removal. However, using only a paper point without
air-blowing produced the lowest bond strength at bothcoronal and apical region of post space. This result
indicates the importance of air-blowing to evaporate
solvent from adhesive layer. Previous studies have
demonstrated that increasing the air-blowing pressure
could improve solvent evaporation from adhesive layer
when the adhesive surface was further away from air-
blowing source (Shinkai et al. 2006, El-Askary & Van
Noort 2011). Therefore, in the apical region, higher
air-blowing pressure would be effective in evaporating
solvent evaporation from the adhesive layer, removing
the pooled adhesive. However, using a higher pressure
might adversely affect bonding at the coronal region,
because it might cause incomplete envelopment of the
collagen fibrils due to excessive removal of the adhesive
resin (Shinkai et al. 2006, Spreafico et al. 2006).
Therefore, the paper point application might be useful
for bonding to root canal dentine.
When additional air-blowing was applied after using
the paper point, cohesive failure in resin decreased and
fewer blisters at the adhesive surface were found
compared with the other experimental group (Figs 1
and 2). These results would indicate that for both mate-
rials, additional air-blowing was effective in evaporat-
ing solvent from the adhesive layer. However, Clearfil
Tri-S Bond Plus with Clearfil DC Core Plus significantlyincreasedlTBS to the apical region, whereas for Clear-
fil DC Bond with Clearfil DC Core Automix, the additive
air-blowing could not improve lTBS to the apical
region. These results might be due to different chemi-
cal-polymerization systems for Clearfil Tri-S Bond Plus
and Clearfil DC Bond. With both materials, lTBS were
lower in the apical region than the coronal region
although Clearfil Tri-S Bond Plus exhibited no signifi-
cant difference in lTBS between the coronal and apical
regions. These results would indicate that the apical
region was not exposed to sufficient light energy for
light-polymerization of the adhesive, and its lTBS was
dependent upon a chemical-polymerization reaction.
Clearfil DC Bond is a two-bottle self-etch dual-cure
adhesive system containing a chemical initiator and
accelerator in different bottles, which slowly chemical-
polymerizes after mixing. On the other hand, Clearfil
Tri-S Bond Plus is developed as one-bottle self-etch
light-cure adhesive with a Touch-cure system, which
Thitthaweerat et al. Solvent evaporation on bonding to root canal dentine
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can rapidly chemical-polymerize in combination with a
chemical accelerator in the adhesive and a specific
chemical initiator in Clearfil DC Core Plus of resin core
material after contact with the adhesive and resin core
material. This different chemical-polymerization behav-
iour might affect lTBS to the apical region. Addition-
ally, Clearfil Tri-S Bond Plus contains multifunctionalhydrophilic monomers as well as 2-hydroxyethyl meth-
acrylate (HEMA), while Clearfil DC Bond contains
HEMA only as hydrophilic monomer. This might con-
tribute to less blister formation in Clearfil Tri-S Bond
Plus than Clearfil DC Bond in each experimental group.
Blister formation would affect the quality of the
adhesive interface to dentine. In this study, it is diffi-
cult to compare quantitatively the blister formation
between each experimental group in the failure analy-
sis because the existence or non-existence of the blis-
ter formation could be confirmed only in the adhesive
failure specimens, but not in the cohesive failure spec-
imens. However, blister formation area would be the
weakest point in the specimen because of less poly-
merization due to residual water content. Therefore,
most of the specimen with the blister formation would
fail in the regions with this area. Further research
should be established to quantitate the blister forma-
tion in adhesive interface between one-step self-etch
adhesive and root canal dentine.
Conclusion
Within the limitations of this study, it can be
concluded that the use of paper points with additionalair-blowing for removing excessive adhesive and
evaporating residual water/solvent would be effective
in producing higher bond strength for one-step self-
etch adhesives (Clearfil Tri-S Bond Plus and Clearfil
DC Bond) and fewer blister formations in deeper
regions of the post space.
Acknowledgements
The authors gratefully acknowledge the financial support
received from the Japanese Ministry of Education, Global
Center of Excellence (GCOE) Program, International
Research Center for Molecular Science in Tooth and
Bone Diseases, Tokyo Medical and Dental University.
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T h i s d o c u m e n t i s a s c a n n e d c o p y o f a p r i n t e d d o c u m e n t . N o w a r r a n t y i s g i v e n a b o u t t h e
a c c u r a c y o f t h e c o p y . U s e r s s h o u l d r e f e r t o t h e o r i g i n a l p u b l i s h e d v e r s i o n o f t h e m a t e r i a l .
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