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Post and Core
Dr. Saritha L.M.
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CONTENTS
Introduction
History
Key words and definitions
Post
Core
Ferrule
Pins
Pretreatment evaluation
Endodontic consideration
Restorative evaluation
Periodontal considerations
Esthetic evaluation
Prosthodontic evaluation
Consideration in restoring endodontically treated teeth
1. Effects of endodontic treatment
a. The role of moisture loss on the nature of dentin
b. Alterations of strength due to architectural changes in the morphology
of the teeth.
c. Concepts of biomechanical behavior of tooth structure under stress.
d. Nature of dentin toughness in pulpless teeth.
e. Changes in the nature of the collagen alignment in pulpless teeth.
2. Anatomic and biologic considerations
a. The amount of remaining tooth structure
b. The anatomic position of the tooth.
c. The functional load on the tooth.
d. The esthetic requirements for the tooth.
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Restoration design and selection
1. Provide a good coronal seal
2. Protect/ conserve remaining tooth structure
3. Satisfy functional and esthetic considerations
Criteria that determine long term prognosis in restoration of endodontically
treated teeth
Timing of tooth restoration
Indications
Anterior
Posterior
Contraindications
Post/ dowel
Definition
Ideal requirements of post and core
Classification of post core.
Factors affecting retention of post systems
1. Post length
2. Post diameter
3. Post design
4. Luting agents
5. Luting methods
6. Canal shape
7. Location in the arch
8. Venting
9. Surface roughness
Retention triad
Post length
Post style
Luting agent
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Resistance triad
Crown bevel
Vertical remaining tooth structure
Antirotation
Factors affecting selection of post and core systems
Types of posts
Custom made post and core
Prefabricated
Custom made post and core
Indications
Contraindications
Advantages
Disadvantages
Prefabricated post
Indications
Contraindications
Advantages
Disadvantages
Clinical procedures for post and core systems
Post space preparation
Removal of gutta percha
Chemical removal
Mechanical removal
Thermal removal
Cast post core fabrication technique
- Direct technique
- Indirect technique
- Fabrication of multiple posts and cores using a thermoplastic material
and indirect technique
- Split cast technique
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Prefabricate dowels and cores
Prefabricated precision plastic dowel
Prefabricated metal dowel core
Prefabricated dowel/ composite resin core
Threaded dowel
Core
Requirements
Materials used: Cast gold
Amalgam
Composite resin
Glass ionomer
RMGIC
Alternative prefabricated post and core systems utilizing material available
Provisional restorations for endodontically treated teeth
Functions
Esthetic role
Protects the tooth from further damage
Prevents migration of adjacent contacting teeth
Provides occlusal function
Different provision restorative materials
Polycarbonate Crown
Clear Plastic Shell
Cementation
Zinc phosphate cement
Polycarboxylate cement
Glass ionomer cement
Resin modified glass ionomer cement
Resin cement
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Stress analysis methods used for post and core
Photoelastic stress analysis
Finite element stress analysis
Post removal
Masserann technique
The Little giant post puller
Kanematsu dowel removing plier
S.S White post extractor
Post puller
Gonon post removing system
Saca Pino post extractor
Ultrsonics
Recent advances
Future trends
Conclusion
Bibliography
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INTRODUCTION
“Teeth and artificial dentures, fastened with posts and gold wire, hold setter than
all others. They sometimes last fifteen to twenty years and even more without
displacement . . .”
Piree Fauchard – 1747.
Endodontic treatment saves the tooth from extraction but only adequate
restoration will reinstate it as a long-term functioning member of the mouth. The
restoration of a tooth by root canal treatment is of limited value unless the crown of tooth
is satisfactorily restored. The manner in which a root canal filled tooth is restored is
therefore considerable importance.
The restoration of endodontically treated tooth is complicated by the fact that
much or all of the coronal tooth structure which normally would be used in the retention
of the restoration has been destroyed by caries, previous restorations, trauma, and the
endodontic access preparation itself.
The endodontically treated tooth is a unique subset of teeth requiring restoration
because of several factors such as dehydrated dentin, decreased, decreased structural
integrity and impaired neurosensory feed back mechanism when compared to a vital
tooth. However, the treatment goal must be based upon a multitude of factors specific for
each patient, so that the strategic architectural aspects that have/greatest impact on the
ultimate strength of the pulpless tooth can be restored/reinforced.
Solution to this problem has challenged the inventiveness and ingenuity of
dentists for centuries.
The endodontically treated tooth must be fortified in such a way that it will
withstand both vertical and lateral forces and not be subjected to fracture. Amalgam as
routinely used to restore a tooth is not considered the best choice, since the cusps are left
unprotected and are subjected to vertical fracture. The use of a crown over an
endodontically treated tooth, by itself is not recommended. Further reduction of already
undermined walls may render the treated tooth subject to horizontal fracture at or near the
gingival line. An inlay, in so far as it too is an intracoronal restoration, leads to same
weakness as the amalgam. This leaves the consideration an onlay, which covers the cusps
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and protects against vertical fracture. Still the potential for horizontal fracture remains,
since the pulp chamber is usually undermined. For these reasons vertical support must be
added to all of the restorations mentioned so that they may be strong enough to protect
the treated tooth from horizontal fracture.
Reinforce the treated tooth and protect against vertical fracture, some type of
stabilization is required that will fasten the restoration to the remaining tooth structure.
This is accomplished by using a post (also referred to a dowel), preferably with a core or
coping and a crown or onlay as superstructure to give coronal-radicular stabilization. A
post and core is a restoration consisting of a post that fills a prepared root canal and a
core inserted into the pulp chamber that establishes the proper coronal tooth preparation.
The post and core is made with a rigid material which, when cemented into the root canal
and pulp chamber provides a solid foundation restoration that is well retained in the
tooth. So the primary function of a post is to aid in retaining a core to restore lost tooth
structure for retention of a restoration and not to provide strength or resistance to fracture.
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HISTORY
Restoration of endodontically treated tooth by a post to retain a crown dates back more
than 250 years.
1728 – Pierre Fauchard described the use of “TENONS”
which were metal posts screwed into the roots of teeth to retain
the prosthesis
1745 – Claude Mouton published his design of a gold crown
with a gold post that was to be inserted into the root.
1830-1870 –Wood replaced metal as the material of choice for
posts.
1839 Harris in proposed that gold and platinum were superior to brass, silver and copper
which tended to corrode.
1849- Tomes proposed the principles of post dimension.
1849 –Dr.F.H.Clark – developed “spring loaded dowel” a retentive device consisting of
a metal tube in the canal & a split metal dowel which was inserted into it. It was designed
to allow for the easy drainage of suppuration from within the canal or apical areas.
G.V. Black developed porcelain fused to metal crown held in by a screw inserted into a
canal filled with gold foil.
1871 – Harries introduced wooden posts. However, they swelled & caused roots fracture.
“Pivot crown” – a wooden post fitted to an artificial crown and to root canal
1884 – Logan crown
1888 – Richmond crown
Later 19th century, single piece post crown.
1930 – custom cast post & core replaced the one piece post crowns or Richmond crown.
1960’s – Prefabricated post – core systems introduced
1990’s (Shillinburg 1997) – widely used prefabricated post – core systems.
1990 Duret et al described a non metallic material for the fabrication of posts based on
carbon fibres reinforcement principle.
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Key words and definitions
Post or dowel: The dowel is a post or other relatively rigid, restorative material placed in
the root of the non-vital teeth. The foremost purpose of the dowel is to provide retention
for the core and coronal restoration.
Core: Is defined as properly shaped and wall restored substructure which replaces
missing coronal structure and retain the final restoration.
Ferrule: Is Defined as a 3600 metal collar of the crown, surrounding the parallel walls of
the dentin extending coronal to the shoulder of the preparation which resists stress
exerted during post insertion.
Pins: Used alone or in combination with posts to provide retention for core material.
Final restoration: The form of crown given after post / core.
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Gutta percha
Post
Core
Final restoration
PRETREATMENT EVALUATION
Before initiation of restorative therapy the tooth must be thoroughly evaluated to ensure
success of all ultimate treatment goals. The tooth should be examined individually and in
the context of its contribution to the overall treatment plan12.
1. Endodontic consideration
2. Restorative evaluation
3. Periodontal considerations
4. Esthetic evaluation
5. Prosthodontic evaluation
Endodontic consideration:
Quality of endodontic treatment is of immense importance prior to restorative procedure,
it is essential that endodontic treatment be successful.
Dense, uniform, three dimensional obturation (fluid impervious seal) of the root
canal system, 0.5 to 1 mm from the radiographic apex of the root/roots is necessary.
Previous endodontic treatment requires evaluation. Should the tooth exhibit signs or
symptoms indicating failure, re-treatment procedures should be accomplished prior to
restoring the tooth. If incomplete root canal fillings, poorly instrumented or condensed
canals, poorly adapted fillings (voids) and untreated canals are evident in the absence of
clinical signs and symptoms indicative of failure, they also should be corrected prior to
the restorative procedures12.
Restorative evaluation
It is essential to determine if the tooth is restorable before endodontic treatment is
performed. Restorative evaluation is mandatory before any definitive therapy.
Successful endodontic treatment is of no value if a tooth is too extensively damaged from
caries, fracture, previous restorations, or periodontal disease to be reliably restored.
Strategic importance of a tooth should be determined before a final plan is formulated.
The reliability and prognosis of a tooth should be considered before the final treatment
plan. The tooth to be retained must be able to withstand the functional forces placed
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upon it after reconstruction. Missing tooth structure can be replaced with a cast
restoration, a core and a dowel.
A critical amount of solid coronal dentin is required, which must encase a coronal
restoration for structural integrity of the restored tooth. The ferrule (i.e. a band of metal
that encircles the external dimension of the residual tooth) has been shown to
significantly reduce the fracture in the endodontically treated teeth.
If insufficient solid tooth structure to accommodate a restoration with ferrule is not
available, the tooth should first be treated periodontally or orthodontically and then
restored. Ferrule effect using a contra bevel in preparation of dowel core acts as an
antirotational device and as positive occlusal seat for the post system12.
Periodontal Considerations
A very important consideration when restoring an endodontically treated tooth is the
periodontium because the ultimate prognosis for a given tooth is dependant on its
periodontal status
Periodontal disease should be treated prior to placement of
definitive restorations.
1. A healthy periodontium provides the best prognosis for
the tooth and will make the procedures such as
placement of margins and making of an impression
easier and more accurate.
2. Whenever there is a substantial loss of tooth structure,
crown lengthening will be required to:
a. Provide adequate isolation for endodontic
therapy
b. Re-establish the biologic width and
c. Provide coronal tooth structure to incorporate a ferrule into the cast
restoration.
2. Dimensions of the attachment apparatus range from 1.77 mm to 2.43 mm. This
means that there should be an absolute minimum of 2.5 mm distance between the
restoration margin and the crest of bone.
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3. Biologic width relates the amount of tooth structure coronal to the osseous crest to
the gingival attachment apparatus.
4. As a general rule, a minimum of 3 mm of sound tooth structure coronal to the
osseous crest will be necessary to accommodate the connective tissue attachment,
the junctional epithelium, and the margin of the crown.
Esthetic evaluation 12 :
Potential esthetic complications should be investigated before initiation of endodontic
therapy.
1. Thin gingiva may transmit a shadow of dark root colour through the tissue.
2. Metal or dark, carbon fibre dowels or amalgam placed in the canal can result in
unacceptable gingival discolouration from the underlying spot.
3. The translucency of all ceramic crowns must be considered in the selection of
dowel and build up materials.
4. Tooth coloured carbon cores, fibreglass reinforced composite resins, or zirconia
dowels can be used in esthetic areas.
5. Similarly tooth coloured, rather than opaque, composite resins should be selected
for the esthetic cases.
6. The colour and translucency of most uncrowned teeth will be adversely affected
by opaque substances.
7. Discolouration from gutta-percha can be visible in the coronal aspect of an
endodontically treated tooth and thus should be limited to an apical level in the
root.
8. Endodontic and restorative materials in these esthetically critical cases must be
selected to provide the best health service with the minimum of esthetic
compromise.
Accurate assimilation of endodontic, periodontal, restorative, and esthetic variables
will contribute to a rational successful treatment outcome.
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Prosthodontic evaluation 12
1. Additional factors affecting prognosis are tooth type, morphology, arch position,
the occlusal and prosthetic forces applied to the tooth and the periodontal support
of the tooth.
2. Tooth structure may be lost due to a variety of reasons: caries, previous
restorative treatment, traumatic injury, attrition, erosion, abrasion, and resorption.
3. Extent of tooth destruction is very important in deciding the restorative technique.
4. Contrary to the popular belief, posts do not strengthen the tooth. Primary function
of the post is to provide retention for the core.
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CONSIDERATIONS IN RESTORING ENDODONTICALLY
TREATED TOOTH
The restoration of endodontically treated teeth has been
the focus of considerable controversy and empiricism. Time-
tested methods have been highly successful in some respects,
but failure is still apparent. Regardless of the system there
should be a through understanding of the anatomy, and biology
of dentin and root supporting the restoration on the part of the
practitioner to support the contention that endodontically
treated teeth have special needs that exceed the requirements of
teeth with vital pulp. These unique aspects include,
A) Effect of endodontic treatment on teeth
B) Anatomic and biologic considerations.
EFFECT OF ENDODONTIC TREATMENT ON TEETH 32
a) The role of moisture loss on the nature of dentin
b) Alterations of strength due to architectural changes in the morphology of
the teeth.
c) Concepts of biomechanical behavior of tooth structure under stress.
d) Nature of dentin toughness in pulpless teeth.
e) Changes in the nature of the collagen alignment in pulpless teeth.
Role of moisture loss:
The moisture content of the coronal dentin is approximately 13.2%. As the age
increases the moisture content decreases due to increased deposition of peritubular dentin
which contains more organic content and water.
Two major components of water content in any calcified tissues are,
1) Outside the calcified matrix,
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2) Within the calcified matrix.
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Water within the calcified matrix is divided in to,
i) Free water to hydrate inorganic ions thus being involved in their
movement – But this water can be removed at between 1000C and 1100C.
ii) Firmly bound water, this doesn’t participate in the movement of ions.
This firmly bound water is called the “water of hydroxyapatite crystal” and is not
substantially reduced until temperature of 6000C is reached.
It is demonstrated that the pulpless tooth contains 9% less moisture than the vital
tooth and this water loss is a irreversible damage and can not be recoverable even in
saturated atmosphere and at body temperature.
Architectural changes:
The decreased strength seen in endodontically treated teeth is primarily because
of the loss of coronal tooth structure. Endodontic procedures reduced tooth stiffness by a
mere 5% attributed primarily by access opening. While a MOD cavity preparation
reduces tooth stiffness by more than 60% with loss of marginal ridge contributing the
greatest loss of tooth strength. With the reduction of the inner cuspal slopes that
unite and support, or exposure of acute cuspal angles a greater chance of fracture exists.
Conversely the excessive removal of radicular dentin during cleaning and shaping
or post space preparation compromises root strength.
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Photoelastic models showing concentration of stress increases at the base of the cusps when the roof of the pulp chamber is
removed
Biomechanical behavior:
The behavior of teeth under load has been investigated and has provided
information into the changes occurring in the pulpless tooth. Tidmarsh described an intact
tooth as a hollow laminated structure that deforms under load. This laminated structure
may shorten, its sides may bulge, and its cusps may be wedged apart by opposing cusps.
Although under physiological loads, complete elastic recovery takes place, permanent
deformation may follow very high / excessive on sustained loads. Therefore the tooth
appears to respond like a prestressed laminate. It is characteristic of such a structure that
it can withstand greater loads in the prestressed rather than in the unstressed state because
in the prestressed state it can flex with the varying degree and angle of load.
How does this prestressed state come about in the tooth?
One hypothesis suggests that as the crown develops, the outward movement of the
ameloblasts and the inward movement of the odontoblasts set up the stressed condition,
which is then frozen or stabilized by mineralization of the matrix.
The significance of this phenomenon is that any cavity preparation, however
small, destroys the prestressed state and releases the stresses.
This phenomenon is crucial if the cuspal inner slopes are removed during
endodontic access preparation or cavity preparation thus destroying the prestressed state.
Subsequently, stress is released, accompanied by a slight shift in cuspal structure.
However, the tooth can deform to a greater extent under applied loads and thus be more
susceptible to fracture. This concept would apply to teeth with endodontic cavity
preparation and would be integrated in the nature of cuspal anatomy, its bucco-lingual
width, and the angle of inclination.
Dentinal toughness:
The toughness is measured by the total energy required to fracture a material.
Another technique to determine the toughness of a material in micro indentation imprints
made in a material with specific loads and the depth of indentation indicates a measure of
hardness of material.
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Dentin exhibits considerable plastic deformation beyond the yield point, it is a
weak biologic ductile material in which strength and toughness may vary.
The shear strengths and toughness values of dentin from endodontically treated
teeth is lower and significantly different from the values for dentin of vital teeth. It is
demonstrated that 14% reduction in the strength and toughness is seen in endodontically
treated teeth.
Collagen alteration:
Dentinal collagen consists of large fibrils characteristic of type I collagen. The
intermolecular cross linking of collagen fibers achieve their characteristic physical
properties of rigidity, resistance of strength and remarkably high tensile strength. It is
verified that there are more immature and fewer mature cross links in root filled teeth –
Accounting for decrease in tensile strength and brittleness of pulpless teeth.
When all above five aspects of dentinal changes are integrated a reasonable
explanation for the changes in the strength of the tooth structure are pulpless teeth can be
formulated. These are fundamental, irreversible changes in the anatomy, biochemistry
and biomechanical properties of dentin which makes up the bulk of remaining tooth
structure after pulpal loss and endodontic treatment. Dentin of pulpless teeth undergoes
alteration in its inherent structure, reducing is tensile strength and flexibility. Because of
the moisture loss and architectural changes of tooth structure – root filled teeth require
unique restorative procedures related to their radicular anatomy and supporting bone.
ANATOMIC AND BIOLOGIC CONSIDERATIONS
Other than the alterations made by endodontic therapy some other important
considerations during post endodontic restorations they are,
a) The amount of remaining tooth structure
b) The anatomic position of the tooth.
c) The functional load on the tooth.
d) The esthetic requirements for the tooth.
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The various combinations of these factors will determine the selection of posts,
cores, crowns and the technique of the treatment procedure.
a) The amount of remaining tooth structure:
The amount of tooth structure damage is one of the most important aspects in
restoration of endodontically treated tooth. The amount of remaining dentin is far more
significant to the long term prognosis of the restored tooth than in the selection of
artificial post, core or crown materials.
Teeth with minimal remaining tooth structure present several clinical problems,
these include.
i) An increased root fracture risk.
ii) A greater potential for recurrent caries.
iii) Greater chance of restoration dislodgement or loss.
iv) An increased incidence of biologic width invasion during preparation.
b) The anatomic position of the tooth:
Anterior teeth:
A nonvital anterior tooth that has lost significant tooth structure requires a crown.
The crown is supported by and retained by the post and core. Desired physical properties
of Posts will determine the selection of materials for the crown, core, post, esthetic post
and core materials are preferred here.
Posterior teeth:
Posterior teeth carry greater occlusal loads than anterior teeth, and restorations
must be planned to protect posterior teeth against fracture. The functional forces against
molars required crown or onlay protection.
c) Functional load of the tooth and prosthetic needs:
The horizontal and torquing forces endured by abutments for fixed or removable
partial dentures dictate more extensive protective and retentive features in the restoration.
Abutment teeth for long span fixed bridges and distal extension, removable partial
denture absorb greater transverse load and require more protection than do abutments of
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smaller bridges or tooth supported removable, partial dentures. Similarly teeth that
exhibit extensive wear from bruxism, heavy occlusion or heavy lateral function require
the full complement of post, core and crown.
d) Esthetic requirements of the tooth:
Esthetic changes occur in endodontically treated teeth. Biomechanically altered
dentin modifies light refraction through the tooth and modifies its appearance. Inadequate
endodontic cleaning and shaping of coronal area also contribute to this discoloration.
Anterior teeth, premolars and often the maxillary first molar inhabit the esthetic zone of
the mouth. These teeth are framed by the gingiva and lips to create an esthetically
pleasing smile. Teeth in the esthetic zone require careful selection of restorative materials
and careful handling of tissues.
ANATOMIC CONSIDERATIONS
Radicular considerations:
There remains a tremendous dependency on the radiograph as the essential
diagnostic aid for determining the anatomy of the root to be restored. While routine
periradicular radiographs provide only two-dimensional cross-sectional anatomy of the
radicular tissues from mesial to distal, supplemental, views from proximal or occlusal
angulation will supply additional information regarding the curvature or extra roots.
However, since the exact facio-lingual dimensions or the mesiodistal shape
including the presence of invaginations or laminations of the roots between the facio-
lingual dimensions of the root cannot be accurately ascertained, it is imperative to have a
thorough knowledge of the root anatomy before reconstructing the tooth.
In teeth that need a post to retain a core build up careful attention must be directed to the
root anatomy for selecting the appropriate post design, including shape, length, and
method of placement.
- Maxillary central and lateral incisors – have sufficient bulk of root to
accommodate most post systems.
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- Care must be exercised in using posts with excessive length if the root tapers
rapidly to the apex – because the thinner the root walls at the depth of the post
placement, the greater the chance for root fracture.
- Maxillary canines – have wide faciolingual roots & root canal spaces that
commonly necessitate a custom cast post for desired adaptation to the root walls
and there is a possibility of proximal root invaginations.
- Restoration of maxillary premolars – presents a variety of problems when one
anticipates a post-retained core. Root walls are commonly thin, and root tapers
rapidly to the apex, especially when two distinct roots are present.
- Proximal invaginations and canal splitting are common during preparation of the
canal from the coronal to apical root structure.
- Root curvatures to the distal are common-preclude using long posts.
- The curvatures of the palatal root can be facial, results in root perforation during
post space preparation or cementation.
- Thinness of these roots – removal of dentin for the placement of a post results in a
weakened root wall which in turn leads to fracture either cementation or during
function.
- Same observations are true for the second premolars, but these teeth generally
have greater bulk of tooth structure.
- Maxillary molar: Suitable root = Palatal root.
Even this root presents restorative problems. 85% of the palatal roots curve
facially and when invaginations are present they are located on the palatal and facial
surfaces. This combination of root curvature and radicular invaginations predisposes the
root walls to weakening or perforation during placement of long or thick posts.
As a result palatal roots can be fractured, requiring root resection, tooth extraction
or surgical endodontics to repair the perforation.
Placement of posts in the MB and DB roots is contraindicated.
Mandibular incisors: Difficult teeth to restore with a post and core – and success rates
have been higher without a post root walls are thin and proximal invaginations are
common.
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Placement of a post is commonly compromised by multiple canals with
significant bone loss, precluding the placement of a post in an unsupported root. This
problem was identified by Reinhardt et al – in teeth restored with a post and core having
diminished bone support of 4-6mm, stress concentration occurs both at the post apex and
on the adjacent root periphery in a relatively narrow band of remaining dentin-potential
for fracture in greater.
Mandibular canines: similar as maxillary canines.
23
Mandibular premolars:
Have sufficient bulk of root structure.
Care must be exercised to ensure that the entire root canal has been managed
become there is a proclivity for multiple canals.
One area of concern: with first premolar is the angle of the crown to the root.
Often the root will be lingual inclined and active drilling of a post space perpendicular to
the occlusal surfaces will result in a perforation along the facial wall of the root.
Mandibular molars: Major problem due to mesiodistal thinness of the mesial and distal
roots. Along the root curvatures, there are commonly invaginations and perforations that
are invisible radiographically.
The roots may be substantially weakened if they are prepared for prefabricated
circular posts – because the roots are externally wide facio-lingually and narrow
mesiodistally. In these cases, fracture may occur during post cementation or patient
function. These types of fractures have been termed “ODONTLATROGENIC” in origin
and should be recognized by the dentist.
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RESTORATIVE DESIGN AND SELECTION
Factors to be considered in design and selection
1. provide a good coronal seal
2. protect/ conserve remaining tooth structure
3. satisfy functional and esthetic considerations
Coronal Seal
Ingress if oral fluids and bacteria leads eventually to sealer dissolution, which
reestablishes a pathway of communication between oral environment and the periapical
tissues. Coronal leakage of bacteria from saliva into root canal fillings material is a
potential cause of failure. This problem may be more pronounced when only a small
volume of obturating materials remain in the canal, such as after post preparation. Hence,
it is necessary that the post endodontic restoration must provide a good coronal seal.
Conservation of tooth structures
A more conservative tooth preparation minimizes the risk of crown an root fracture. With
narrow single rooted teeth such as mandibular incisors preservation of tooth structure is
especially important, and custom cast post, have been reported to offer better retention
and resistance to fracture compared with parallel sided serrated posts. Strict adherence to
the guideline of parallelism of the post space may result in over preparation of the apical
termination of the post preparation that can also concentrate stresses where the radicular
dentin is thinned and weakened. Slightly tapered posts are easier to prepare and more
conservative, because most roots are tapered. The gutta percha filling is removed to the
desired depth and residual endodontic sealer or undercut are eliminated. The resultant
slightly tapered post is designed to fit the available space.
Reinforcement and retention
Pulpless teeth frequently remain relatively intact after endodontic treatment with
conservative access. Although, it has never been adequately demonstrated that an
endodontically treated tooth is more brittle than a vital tooth, fracture s of pulpless teeth
25
during mastication have occurred. Restoration and reinforcement ofpupless teeth is an
important preventive measure in endodontic treatment since, failure to do so may invite
future problems or embarrassing mishaps.
26
CRITERIA THAT DETERMINE LONG-TERM PROGNOSIS IN
RESTORATION OF ENDODONTICALLY TREATED TEETH: Journal of
Esthetic Dentistry 1998; 10(2): 75-83
CRITERIA PARAMETER VARIABLE
Force Intensity Area of mouth, Jaw angle, Muscle
strength, Parafunctional habits, Type of
contact/food, crown to root ratio,
periodontal support tooth mobility.
Frequency Chewing, Clenching, Grinding
Parafunctional
Duration, Direction
(lateral/rotational/
compressive/
retentive )
Tooth, cusp, Occlusal table, inclination,
position, Size
Restoration
Component
Interface
Operative
Restoration
Core, Post, Cement,
Tooth
Restoration to core, to
post, to cement, to
Material strength: Compression,
shear/tensile, elasticity modulus, modulus
of deformation, yield strength, pre-stress
effects, thermal coefficient of expansion,
internal stress, stability and fatigue.
Surface area: Overall height, width,
length, cross sectional shape, box
formation, micro/macro mechanical
contact, chamber shape, box formation,
pins.
Mechanical contact: size of contact,
position and type (flat, point, wedge).
Interaction of material:
Wetability, chemical interaction,
oxidation, electrolysis, mechanical wear,
stress, mechanical wedging, thermal
27
tooth coefficient of expansion
Timing of tooth restoration:
1. Until an endodontically treated tooth is restored to full function, treatment is
incomplete.
2. Coronal leakage is a significant etiology in endodontic failure.
3. If obturated canal is exposed to saliva, leakage will occur and compromise the
gutta-percha seal, and the tooth may require re-treatment.
4. Unrestored endodontically treated tooth is more susceptible to fracture.
5. Modern endodontic therapy achieves a predictably high success rate; postponing
restoration for extended periods of time to be certain of endodontic success is
unnecessary and could place the tooth at risk.
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INDICATIONS
Anterior
1. Where the natural crown of root-filled teeth either has been lost / extensively damaged.
2. If complete coverage restoration is indicated for endodontically treated teeth for
esthetics or functions.
3. Functional requirements- if there is a doubt regarding the adequacy of the resistance
form of the coronal portion of the tooth to support the crown
4. Malaligned teeth
5. Loss of two proximal surfaces with a lingual endodontic access opening which
weakens the tooth.
6. Where the root-filled tooth is to be used as bridge abutment.
7. Where a change in axial position greater than 1mm is required.
Posterior
1. When other more conservative retention and resistance features cannot be used for core
like chamber retention, amalgam pins etc
2. When a tooth is to serve as an abutment for a removable partial denture
3. In premolars if the remaining coronal tooth structure is inadequate, the clinical crown
is tall in relation to its diameter at the point where it enters the alveolar bone, or if the
tooth receives significant lateral stresses
4. In case of malposed teeth, when preparation of tooth would cause exposure of the
pulp- of choice for aligning coronal portion of the tooth.
29
CONTRAINDICATIONS
1. Severe curvature of the root-eg: Dilacerations of the root.
2. Persistent periapical lesion
3. Poor periodontal health
4. Poor crown to root ratio
5. Weak / fragile roots
6. Teeth with heavy occlusal contacts
7. Patients with unusual occupational habits
8. Economic factor & inadequate skill
30
POST
Dowel/Post: The dowel is a post or other relatively rigid, restorative material placed in
the root of the non-vital teeth. The foremost purpose of the dowel is to provide retention
for the core and coronal restoration.
The dowel is especially important in restoration of non-vital teeth that have suffered
significant damage and have insufficient sound tooth structure remaining above the
periodontal attachment to secure a coronal restoration. The dowel itself does not strength
a tooth, on the contrary, the tooth is weakened if dentin is sacrificed to place a large
diameter dowel.
Ideal properties of the dowel:
1. Maximum protection of the root.
2. Adequate retention within the root.
3. Maximum retention of the core and crown.
4. Maximum protection of the crown-margin- cement seal
5. Pleasing esthetics, when indicated.
6. High radiographic visibility.
7. Retrievability.
8. Biocompatibility.
9. Material compatibility with core.
10. Minimum stress during placement and cementation tissue.
11. Ease of use, safety, reliability
12. Distribution of functional stresses evenly along the root surfaces.
13. Physical properties similar to dentin
14. Reasonable cost.
31
CLASSIFICATION OF POSTS
I. A. Custom cast Posts:
1. Endopost2. Endowel3. ParapostB. Prefabricated posts:
1. Parallel sided – serrated and vented. Eg. Para post.2. Tapered self threading systems. Eg. Dentatus.3. Tapered smooth sided systems. Eg. Kerr, Ash.4. Parallel sided threaded post systems.Eg.Radix Anchor, Kurer Anchor post system.5. Parallel sided, threaded, split shank systems. Eg. Flexi post.
II. A. Passive retention posts:
1. Cast posts2. Smooth tapered posts3. Serrated parallel postsB. Active retention posts:1. Flexi posts2. Kurer Anchor posts
III. Types of non-metal posts:
A. Based on composite materials:1. Carbon Fibre posts:
a. Composipost b. Carbonite c. Endopost d. Mirafit carbon
2. Silica Fibre posts:a. Aesthetipost b. Aesthetiplusc. Light post d. Snow post e. Parapost fibre whitef. Fibre-kor
3. Light transmitting posts:a. Light post b. Luscent anchor post
4. Ribbon fibre posts
B. Based on ceramics:
1. Cosmopost
32
Wedge or conically shaped posts:A. Threaded and taperedB. Smooth conical with groovesC. Serrated and conical
Parallel sided posts:A. Threaded and parallelB. Parallel and self threadingC. Parallel and serrated
33
NEW RESTORATIVE CLASSIFICATION OF ENDODONTICALLY TREATED
TEETH : By Paul R. Chalifoux
The classification is based on the number of canals, amount of coronal tooth structure,
chamber space, canal quality, and orientation.
Classes 1,2 &3 refer to teeth with one, two or three canals. Each of these
classifications is further subdivided into complete (c), partial (p) & no (n) coronal tooth
structure. Complete coronal tooth structure comprises a range of 66-100%, partial, 33 to
65% and no.0 to 32%. The percentage of remaining coronal tooth structure, after root
canal and restoration preparation is defined as the least of the two percentages:
Class Tooth structure
1 (one canal) Complete (C), partial (P), No (N)
2 (two canals) Complete (C), partial (P), No (N)
3 (three canals) Complete (C), partial (P), No (N)
C = 66-100%, P = 33-65%, N = 0-32%
Sub classification :
Chamber space Present Interlocking, limited interlocking, non-interlocking
Absent
Canal quality Shape Segmented: straight, curve Uniform: straight, curved
Size Diameter: uniform, segmented Length: straight, normal, long
Taper Uniform: parallel, tapered Segmented: parallel, tapered
Canal orientation Parallel interlocking
Canal-canal, canal-component
34
FACTORS AFFECTING RETENTION OF POST SYSTEMS
(Journal of prosthetic dentistry 1999, 81(4): 380-385
1. Post length:
a. Should be longer than crown.
b. At least 1/3rd the length of crown.
c. Should be a certain fraction of the root length: such as 1/2, 2/3.
d. End halfway between the crestal bone and root apex.
e. As long as possible without disturbing apical seal.
2. Post diameter:
a. Increasing diameter does not provide significant retention.
b. Increases stiffness of the post at the expense of the remaining dentin and the
fracture resistance of the root decreases.
c. Goodacre-post diameters should not exceed 1/3rd of the root diameter at any
location.
d. Post diameter must be controlled to preserve radicular dentin, reduce the
potential for perforation and permit the tooth to resist fracture.
Three different philosophies regarding post diameter:
1. Conservative approach: Advocated by Mattison – to restrict the diameter of the
post to conserve the remaining tooth structure. Increase in post diameter-elevates
stress in the radicular surface.
2. Proportionist approach: Advocated by Stern and Hirschfeld – optimal diameter
one-third the diameter of the root. It preserves sufficient tooth structure.
3. Preservationist approach: advocated by Halle et al – proposed the preservation of
at least 1.75 mm of sound dentin around the entire circumference of the post-
sufficient to resist fracture of the tooth.
35
For selecting the post diameter – suggested that the proportionist and
preservationist approach be applied.
3. Post design:
Tapered posts produced the greatest stress at the coronal shoulder, & parallel
posts generated greatest stress at the apex of the canal preparation. Of the threaded
designs, the tapered screw produced the greatest wedging effect & highest stress levels.
The parallel sided, serrated, vented post produced stresses that were distributed most
uniformly along its length and appeared best able to protect the dentin. Parallel sided
threaded posts that are tapered may be considered when additional retention is needed.
4. Luting Agents:
a. Luting agents, including zinc phosphate, polycarboxylate, glass ionomer & filled
and unfilled resin cements have been investigated extensively.
b. Both zinc phosphate and glass ionomer cements are frequently used because of
their ease of manipulation along with their history of success in luting procedures
5. Luting methods:
Methods of applying luting agent into the canal space
a. Lentulospiral, b.Paper point,
c.Endodontic explorer. d.Needle tube
After luting agent is placed in the canal, post is coated with the luting agent & inserted.
6. Canal shape:
Predominant canal shape is ovoid and the walls of prefabricated posts are
parallel.
Preparation of the canal space and tooth
a. Methods used are: rotary instruments, heated instruments and solvents.
b. Minimum of 3 to 5 mm of gutta-percha must remain to preserve apical seal.
36
c. For each prefabricated system, the accompanying twist drill is then used to shape
the canal following the direction and depth created by the hand instruments.
d. Stops should be placed on engine driven drills at the desired depth as an added
precaution.
7. Location in the dental arch:
The location of the tooth in the dental arch necessitates different restorative
requirements to ensure the longevity of endodontically treated teeth.
8. Venting
Because of intraradicular hydrostatic pressure created during cementation of the
post, a means for cement to escape must be provided. A vent may be incorporated in the
pattern before casting or cut into the post with a bur prior to cementation.
9. Surface roughness
Surface roughening, such as air abrading or notching, of the post increases post
retention
37
Retention Triad68
Retention is defined as the force that resists a tensile or pulling force.
Retention can be gained in three ways
1. Adequate post length in the canal
2. post style if canal length is inadequate to retain the post in the canal then the
active post should be used
3. luting agent used to cement the post
Resistance Triad68
Resistance can be achieved by
1. Crown bevel- the bevel is that part of the crown margin that extends past the post
and core margin onto the natural tooth structure.
- to be effective it should encircle the tooth(360degrees) and ideally extend at
least 1.5mm onto the tooth structure below the post and core margin
2. Vertical remaining tooth structure- leaving as much as natural vertical
remaining tooth structure as possible will significantly increase the resistance of
the final restoration
3. Antirotation- an oblong or elongated canal orifice can provide the antirotation
- auxillary pins and keyways, prepared in the face of the root
1. The first feature of the resistance triad is the ferrule :
The Ferrule is a metal ring or cap intended for strengthening. The word probably
originates from combining the Latin for iron (ferrum) and bracelets (viriola) (Brown,
1993).
Ferrule = ferrum + viriola (Latin term)
A dental ferrule is an encircling band of cast metal around the coronal surface of
the tooth. It has been proposed that the use of a ferrule as part of the core or artificial
crown may be of benefit in reinforcing root-filed tooth.
38
A protective, or “ferrule effect” should occur owing to the ferrule resisting
stresses such as functional lever forces, the wedging effect of tapered posts and the lateral
forces exerted during the post insertion.
Rosen proposed the concept of an “extracoronal brace” subgingival collar or
apron of gold which extends as far as possible beyond the gingival seat of the core and
completely surrounds the perimeter of the cervical part of the tooth. It is an extension of
the restoration crown, which by its hugging action prevents shattering of the root.
The collar significantly reduced the incidence of root fracture.
To be effective – it must encircle the tooth (3600) and ideally extend at least
1.5mm onto tooth structure below the post and core margin.
2. Vertical remaining tooth structure :
Traditionally, it was thought that the face of the root should be flattened prior to
the construction of the post and core. However, it has been shown that leaving as much
natural remaining tooth structure as possible will significantly increase the resistance of
the final restoration. Unfortunately, because of caries, trauma, or iatrogenic removal,
vertical remaining tooth structure is not always available.
3. Antirotation :
Every post & core must have an antirotation feature incorporated in the preparation.
An elongated or oblong canal orifice can serve as an antirotation for post and core.
However, as the canal becomes more round, the need for incorporation of
antirotation features becomes more important. This is especially true for anterior
teeth. Auxillary pins and keyways are prepared in the face of the root prior to
construction of the post and are most common antirotation devices.
39
FACTORS AFFECTING SELECTION OF POST AND CORE SYSTEM
1. Root length
2. Tooth anatomy
3. Post width
4. Canal configuration and post adaptability
5. Coronal structure
6. Stress
7. Torsional force
8. Role of hydrostatic pressure
9. Post design
10. Post material
11. Material compatibility
12. Bonding ability
13. Core retention
14. Retrievability
15. Esthetics
40
CUSTOM CAST POSTS:
Currently, the clinician can choose from a variety of post system for different endodontic
and restorative requirement. However, no single system provides the perfect restorative
solution for every clinical situation and it requires an individual evaluation.
The traditional customs cast dowel core can be made by reliving a plastic sprue with
acrylic or a metal pin with wax to form the post. The same material can be used for core
formation.
Advantages
1. They are custom fit to the root configuration.
2. Provide a better geometric adaptation to excessively flared, elliptical, tapered,
noncircular or irregular shape canals.
3. Excellent core retention.
4. Greater strength in the sections.
5. This two-step procedure improves the marginal adaptation and allows for a
variation in the path of insertion of the crown.
6. It almost always requires minimum tooth structure removal
7. Custom cast post and cores adapt well to extremely tapered canals or those with a
non-circular cross-section or irregular shape, and roots with minimal remaining
coronal tooth structure
Disadvantages
1. Root fractures - the modulus of elasticity of cast metal is 10 times greater than that of
dentin leading to greater stress concentration and subsequent root fracture.
2. The transmission of occlusal forces thorugh the metal cores can focus stresses at
specific regions of the root, causing root fracture
41
2. Aesthetics – metal post alter the light transmission through the tooth and may show
through the root especially where the gingiva is thin.
a.The corrosion products may pass into the root, discolouring the tooth
b. Metal core will also alter the optical properties of overlying ceramic restoration.
3. Biocompatibility – non precious metals show corrosion with in the root which has been
implicated as a cause of root fracture.
4. This method requires two-appointment visits and a laboratory fee.
Indications for custom cast post
1. When multiple cores are being placed in the same arch- It is more cost effective to
prepare multiple post spaces, make an impression & fabricate the posts in
laboratory.
2. When post & cores are being placed in small teeth (mandibular incisors). In these
circumstances, it is often difficult to retain the core material on the post.
3. When the angle of the core must be changed in relation to the post, prefabricated
posts should not be bent; therefore, the custom– cast best fulfills this requirement.
4. When an all-ceramic non-core restoration is placed it is necessary to have a core
that approximates the color of natural tooth structure. If a large core is being
placed in a high-stress situation, resin composite may not be the material of
choice due to the fact that it tends to deform under a load. In this circumstance,
the post & core can be cast in metal, & porcelain can be fixed to the core to
simulate the color of natural tooth structure.
42
PREFABRICATED POSTS AND CORES
The prefabricated dowel may be a metal dowel to which a custom core is cast. It can be a
dowel which can be cemented into the canal with an amalgam or composite core formed
around it. Finally, the dowel may be standardized precision plastic pattern to which a
custom core is added before investing and casting.
The principle employed is to make the canal fit the post rather than making the post fit
the canal.
ADVANTAGES OF PREFABRICATED POSTS:
Simple to use
Less time consuming
Single appointment procedure.
Easy to temporize.
Cost effective
Strong
DISADVANTAGES OF PREFABRICATED POSTS:
- Root is designed to receive the post, rather than post being designed to fit the root.
- Application is limited when considerable tooth structure is lost.
- Chemical reactions are possible when post and core are made of dissimilar metals.
- Attachments for removable prosthesis cannot be applied to post core unless a separate
casting is fabricated to be placed over it.
- Loss of retention of post and core.
Considering the major drawbacks of the metal post systems (Custom and
prefabricated post system), researchers have evolved with the fiber reinforced composite
post systems. These serve to alter not only the procedures, but the very paradigms of
treatment. These include
-> Minimal invasiveness of the remaining post endodontic dentin.
The biocompatibility of restorative materials (Posts, cores and cements) to the
remaining natural tooth structures
The esthetic compatibility of both the post and the core and easy retrievability.
43
Some prefabricated post and core systems available are
1. Prefabricated precision plastic dowel
a. parallel
b. tapered
2. Prefabricated dowel/ cast core
3. Prefabricated dowel/ composite core
4. Prefabricated parallel threaded dowel
5. Parallel self threading dowel
6. Amalgam pin core
7. Composite resin core
44
GUTTA PERCHA REMOVAL
Chemical removal
Solvents such as oil of eucalyptus, oil of turpetine and chloroform have been used to
soften gutta-percha for removal, with the latter two being the most efficient. However,
some of these materials and especially chloroform are hazardous to use as they are toxic
and potentially carcinogenic. Oil of turpentine is less toxic, but there is concern that
solvents in general lead to a dimensional change in the gutta-percha, leading to increased
microleakage.
Disadvantages –
1. difficult to control the depth of softening of the gutta-percha
2. potential leakage of the solvents into the periradicular tissues
Thermal removal
A heated instrument such as a lateral compactor can be inserted into the gutta-percha to
the desired length to soften and remove the guttapercha. However, in narrow canals, fine
instruments lose their heat quickly and gutta-percha removal can be difficult. A System B
spreader is ideal for removal or gutta-percha.
Procedure-
From a pre-operative radiograph a plugger should be chosen of the correct dimensions
that is likely to bind at the desired post length and this position should be marked on the
plugger with a rubber stop. The tip should be placed in the gutta-percha and with the heat
applied driven slowly to the desired post length in about 2-3 seconds. The heat should be
removed and the plugger allowed to cool, for about 7-10 seconds, twisted and then
removed with the coronal gutta-percha. Alternatively, a short burst of heat to the plugger
will allow for easy removal. It is important that the plugger is sufficiently hot to
completely soften the gutta-percha. If too cool it will result in the gutta-percha remaining
sticky with the risk of dislodging the apical gutta-percha. An instrument such as a
Buchanan plugger can then be used to vertically compact the softened gutta-percha.
45
Mechanical removal
Mechanical removal of gutta-percha is efficient and probably the most commonly used
technique, but it is a technique that can result in the most damage to tooth tissue. If
done incorrectly it can weaken the root unnecessarily, damage the periodontium and in
some cases lead to root perforation. A non-end cutting; bur such Gates Gliden or Peeso
reamer should be used for gutta-percha removal, as these will cut and remove the
relatively softer gutta percha preferentially to the dentine of the canal walls.
The sequence in which the burs are used is be important so that a rise in temperature
at the root surface, which could damage periodontal cells, is avoided and the risk of
preferentially cutting away root dentine to one side of the root canal is reduced.
Temperature rise on the root surface has been investigated in a number of studies. The
Gates-Glidden bur rotating at 8000rev/min results in a small rise in temperature at the
root surface.
However, both tapered and parallel-sided post star drills produce a significant increase
in temperature in -excess of 17◦C. Peeso reamers also generate significant rises in
temperature, higher than that reached with Gates-Glidden burs and Parapost twist drills.
46
INSTRUMENTATION
A wide variety of instruments can be used for enlarging the root canal for a post:
Safe-ended reamers
Hand file
Standard burs with long shanks.
The preparation is begun by placing a hot endodontic plugger approximately half the
length of the canal. This is followed by the actual post preparation. Peeso reamers or
Gates Glidden drills are widely used for preparing the post space. Begin with the largest
size that will fit easily into the canal. Prepare the canal to the complete predetermined
length. Then switch to the next largest instrument in the graduated series and repeat the
process. Do this until the desired diameter has been attained. The instrument is leaned
over lightly as it is withdrawn from the mouth of the canal. This will result in an essential
parallel-sided preparation with a tapered orifice.
Gates Glidden drill
- a non-cutting tip
- numbered 1-6, range in diameter from 0.5 to 1.5 mm in
graduated increments of 0.2 mm.
- shorter cutting flutes (1.5-4.0mm)
- instruments measure 18 mm from the cutting end
- ISO standardization – 50-150.
Advantages of using gates glidden drills-
- Cutting portion is smaller and more maneuverable
- Easier to use in starting very small canals - Shorter cutting flutes and more
flexible shafts
Peeso reamer
- non-cutting tip
- numbered 1-6, range in diameter from 0.7 to 1.7 mm in
graduated increments of 0.2 mm.
- Longer cutting flutes (7.5-8.5mm).
47
- instruments measure 18 mm from the cutting end
- ISO standardization – 70-170.
Advantages
- have a sharp, but noncutting tip, they will follow the path of least resistance
- conform more consistently to the original canal in the apical region than will
other types of instruments
Peeso Reamer Sizes:
Reamer
Number
Diameter Teeth
1 0.7mm Mandibular incisor
2 0.9mm Maxillary first premolar
Maxillary second molar (DF)
Mandibular first molar (ML)
Mandibular second molar (MF, ML)
3 1.1mm Maxillary second premolar
Maxillary first molar (MF, DF)
Maxillary second molar (MF)
Mandibular first molar (MF, D)
Mandibular second molar (D)
4. 1.3 mm Maxillary lateral incisor
Mandibular premolar
Maxillary molar (L)
5 1.5mm Canine
6 1.7 mm Maxillary central incisor.
48
Custom Post-Core :
Custom post-core can be fabricated in two techniques :
Direct - fabricated directly in the mouth on the prepared tooth.
Indirect- utilizes an impression and stone die of the tooth for pattern fabrication. The
pattern from either the direct or indirect technique is then invested and cast with gold or
any other crown and bridge alloy.
Direct technique
The direct custom post core is made by fabricating a resin or wax pattern in the
prepared tooth in the patient’s mouth. Some form of plastic post or thin metal post is used
as the central reinforcement around which the resin or wax pattern is formed.
The pattern can be made of wax reinforced with a plastic rod, a bur, a metal pin or
a paper clip. Acrylic resin can also be used for this purpose or wax and acrylic can be
combined. The use of resin allows the pattern to be formed into a well adapted solid post
that can be manipulated easily in the mouth without becoming distorted or loose in the
canal.
After removing as much gutta-percha as possible with a hot endodontic plugger,
begin the actual canal preparation with the largest reamer which will fit into the canal.
Make a radiograph to check the accuracy of the preparation depth. Use the radiograph
to make any necessary adjustments in the reamer length.
A keyway is placed in the orifice of the canal to provide anti-rotational stability to the
post. One or more vertical grooves are cut in the walls of the canals, extending 3-4
mm down the canal. The same effect can be achieved on a multi rooted tooth by
placing a short post into a second canal.
The keyway should be cut to the depth of the diameter of a No. 170 bur (nearly 1.0
mm) in the area of greatest bulk. A second opposing keyway is placed in larger root.
Add a prominent contrabevel to provide a collar around the occlusal circumference of
the preparation. It will aid in holding the tooth together and preventing fracture. This
49
serves as a safeguard on a precision fitting post, which can exert lateral forces during
cementation.
The post-core pattern will be fabricated with a plastic screw and resin . Once the
preparation is ready for the fabrication of direct pattern, wrap a cotton pellet tightly
around a No.1 Peeso reamer and dip it into the duralay lubricant. The cotton should
be completely coated with the lubricant.
Insert the peeso reamer to the entire length of the post preparation. Then pump the
reamer in and out to make sure that the entire canal is well coated. Some of the
lubricant should be on the coronal part of the preparation as well.
Use 14 gauge plastic sprues for the pattern. They are hard enough to reinforce the
pattern and they will burnout cleanly. Plastic tooth picks are softened by the monomer
and often are separated from the pattern during removal.
Trim the sprue with a garnet disc so that it will fit into the canal easily. It must reach
the apical end of the post preparation. Cut a small notch in the facial portion of the
occlusal end of the plastic sprue to aid in orienting the pattern in subsequent steps.
Coat the plastic sprue with monomer.
Mix the duralay monomer and polymer to a thin, runny consistency in a dappen dish
and fill the mouth of the lubricated canal as completely as possible with a plastic
filling instrument.
Coat the plastic sprue with the acrylic while it is still fluid.
Seat the resin covered sprue in the canal until it has touched the apical end of the post
preparation. Make sure that all the external contrabevel is covered at this time.
More resin is added to the coronal portion of the pattern to provide the bulk for the
core. It can be added while the post is still polymerizing or it can be added as a fresh
mix to the polymerized post.
When the resin on the post itself becomes doughy, pump the pattern up and down to
prevent its being locked into any undercuts in the canal.
Remove the post from the canal and see if it extends the full length of the prepared
canal. Fill any voids with soft utility wax and replace the pattern.
Shape the coronal portion of the pattern to form it into a crown preparation for the
final restoration.
50
Remove the pattern from the mouth end roughly shape the axial surface with a garnet
disc. Replace it in the tooth from time to time to ensure that the contours being
shaped are consistent with the remaining coronal tooth structure. Be sure that the
finish line of the final crown preparation is on tooth structure and not on the core.
After complete finishing of core pattern, it is cast in gold or nickel –chrome alloy.
The core portion of the casting should be smoothened to a satin or matte finish.
Use a carbide no:34 bur to cut a V-shaped cement escape vent on the side of the post.
This groove should help greatly to prevent damaging lateral stresses during
cementation. While using the hard nickel-chrome alloys, this task can be made easier
and faster by placing the groove in the acrylic pattern and retouching it in the finished
casting.
Prepare a thin mix of zinc phosphate cement and insert some into the mouth of the
dried, isolated canal. Cover the blade of the instrument with cement a second time
and hold it incisal to the mouth of the canal. Insert slowly rotating lentulo spiral paste
filler through the mass of the liquid cement to carry the cement into the canal. Apply
more cement to the mouth of the canal until no more will move into the canal.
Liberally coat the post with the fluid cement and insert the post into the canal.
Seat the post slowly with finger pressure, allowing the cement to escape ahead of the
post. If the incisal edge of the core is uncomfortable against the finger, cushion it with
a cotton roll. Never mallet the post to place. The close fitting hydraulic chamber
formed by a custom post moving through a viscous liquid in a parallel walled canal
can produce considerable stress in the lateral walls of the tooth, and fracture could
result.
When the cement has set , go over the axial surfaces of the core and tooth structure
with a fine grit diamond as it is important to remove any minor undercuts in the axial
surfaces near the margin of the post-core. If allowed to remain, any defects in the
axial surface could present obstacles to the successful completion of the final
restoration.
The tooth can now be restored with a crown. The portion of the coronal tooth form
that has been built up with the core can be treated as though it were tooth structure
when the final restoration is fabricated.
51
52
Post space preparation
Fabrication of Wax pattern
Indirect technique
A custom post-core can also be fabricated by making wax or resin pattern on a
cast of the prepared tooth.
An impression can be made by injecting impression material into the canal and
then using a lentulo spiral paste filler to ensure the elimination of entrapped air and voids
in the impression of the canal. The impression is reinforced with some type of rigid post.
The items that have been used for this purpose are paper clips, short lengths of wire,
plastic sprues, and a root canal instrument.
These reinforcing devices not only strengthen
the impression when it is made, but also when it
is poured and separated.
A custom acrylic post can also be made in the tooth to serve as the impression of
the canal in transferring it to a cast for fabrication of the core and restoration. When the
indirect technique is used with one of the prefabricated precision plastic patterns, a post
pattern is placed into the canal, and it is picked up in the impression. The post then
creates its own space in the cast when the impression is poured.
While any impression material with which the operator is familiar can be used, light
body elastomeric materials which are more flexible is preferred.
Once the cast is poured, a removable die should be fabricated. The cast is mounted in
a Di-Lok tray. This permits the use of a
removable die without any possible
interference between a post pin on the
bottom of the die and the post core
preparation deep within the die.
The wax pattern can now be fabricated on
the die and working cast.
53
Lubricate the die copiously with a die lubricant. Make sure the post preparation is
well filled.
Dead soft,12 gauge round wax forms can be used to form the post. It is placed into
the bottom of the canal in the lubricated die. Cut it off flush with the top of the
coronal tooth structure with a sharp laboratory knife.
Grasp a piece of wire such as a straightened paper clip in cotton pliers and heat it in
the flame of a Bunsen burner. Plunge the hot wire into the canal until it touches the
bottom, melting all the wax in the canal. Hold it steady until the wire cools and the
wax solidifies.
Gently pump the wire and soft wax post in and out a few times to make sure that it is
easily removable from the die.
Use regular inlay wax to build up the core portion of the wax pattern.
Finish the margins of the core with a warm beaver tail burnisher to produce as well
fitting a casting as possible.
The completed wax pattern will have the paper clip protruding from the incisal edge
or lingual surface. The wire will serve as the main support of the sprue. Soft wax is
added to the wire to thicken it to the diameter of a 10 or 12 gauge sprue.
Investing and casting can be done in the regular way. Place the completed post -core
in the die, making sure that it is completely seated.
Relubricate the die and lubricate the core. Then wax a coping for the porcelain fused
to metal crown.
Seat the cast coping back on the post core in
the die. The marginal adaptation should be
good and the fit of the coping over the post
core and die should be passive, i.e., there
should be no binding.
Porcelain fused to metal restoration is
fabricated.
54
CUSTOM DOWEL CORE (TWO PIECE) :
However, if a severely damaged tooth is to be subjected to the stresses of acting
as an abutment for a fixed bridge or removable partial denture, more resistance and
retention are required. Because of the root divergence found in most molars, using a
dowel-core with two or three parallel dowels extended into multiple roots can be quite
hazardous. Therefore a multi-piece dowel core with separate dowels should be employed.
The dowel-core for a mandibular molar is usually divided into mesial and distal
segments. The maxillary molar dowel –core is composed of facial and lingual
components with the dowels in the two facial canals paralleling each other. When the
mesiofacial and distofacial canals are too divergent to permit parallel dowels, a separate
third dowel is required.
For a two piece dowel-core to achieve maximum strength and retention from the
dowels in divergent canals, the pieces must be rigidly bound together after insertion. A
number of indigenious methods have been proposed for accomplishing this. The core can
be made in two halves, held together by interlocking lugs, which can be formed from a
commercially available non-rigid connector pattern or by cutting a keyway or dovetail in
one half of the core pattern.
A commonly used solution for the problem is the fabrication of the core with an
integral dowel and a channel in the core through which an accessory dowel is cemented.
The hole for the interlocking accessory dowel is aligned with a preparation in another
diverging canal. The accessory dowel acts as a dowel-core within a dowel-core and its
divergent direction helps to nail the core in place. The secondary dowel can be a
prefabricated post or wire, or it can be a cast custom dowel. A variation on this theme
uses a core with no attached dowel. It is pierced with channels for two or three diverging
separate dowels which, when inserted and cemented, will hold the core firmly in position.
Finally the core be fabricated in two halves with pin holes in the first half and
interlocking pins in the second half. The core is pinned together when both halves have
been cemented in the tooth.
55
Any of these interlocking methods can be fabricated by the direct technique or by
the indirect technique of which the latter technique seems to be far more expeditious and
simple.
In indirect technique, it is important to obtain an accurate impression of the canal
preparation. A short segment of wire (paper clip) is placed in each canal to
reinforce the impression dowel . Once the cast is ready, the wax pattern for the
facial half of the dowel core will be fabricated first. On a mandibular tooth, it
would be mesial half.
Gauged, plastic sprues are tried into the two facial canals. Trim them with coarse
garnet discs so they will fit easily to the bottom of their respective dowel
preparation.
After sufficient lubrication, place soft round wax forms into each of the two facial
canals. Cut them off flush with the root face of the tooth.
Plunge a hot PKT no.1 instrument to the bottom of each of the canals, melting the
soft wax completely. While the wax in the facial canals is still soft, insert the
trimmed solid plastic sprues into the wax and shove each of them to the bottom of
its respective canal.
To provide the locking mechanism for tying the two halves of the core together
after cementation, pin holes are drilled in the facial half of the core.
The facial half of a core is then produced. The external axial contours of the facial
half will be consistent with the axial walls of a full crown preparation. The lingual
surface will be flat smooth surface, which parallels the path of insertion of the
palatal canal. Use an enamel hatchet for core and 1.5 mm wide ledge or shoulder
in the occlusal third of the lingual surface.
Carefully align a 0.7 mm drill with the path of insertion of the palatal canal.
Drill the pin holes in the ledge, making them parallel with each other and the path
of insertion of the palatal canal. For maximum effectiveness, they should extent
the full length of the core.
A short section of thin pencil lead is placed in each pinhole before investing. This
will keep the holes patent during burnout and casting. About 2 mm of graphite
56
should show at each end of the pin hole to ensure that the rods will be held
securely by the investment.
The pattern is invested, burned out, and cast .A gold alloy should be used because
graphite rods are employed to maintain the pin holes. The contamination of a
chromium containing alloy with carbon will increase brittleness and decrease
corrosion resistance. Use the 0.7 mm drill to remove the graphite from the pin
holes. Once the casting for the facial half of the dowel core has been fabricated,
the lingual half can be made against it on the cast.
Seat the completed facial of the dowel-core into the facial canals. Check to make
sure that the lingual surface and the two pin holes are parallel with the dowel
preparation in the palatal canal.
Insert nylon bristles into each of the pin holes and lubricate the lingual surface of
the facial core. Relubricate the palatal canal profusely.
Try a 14 gauge plastic sprue into the palatal canal. Trim the sides of the spring
with a coarse garnet disc to allow the sprue to slip easily to the bottom of the
canal.
Wax or acrylic resin can be used to build the pattern. A fresh mix of resin is
placed in the mouth of the canal, and the trimmed plastic sprue is seated to place.
When the acrylic is near polymerization, pump the sprue in and out several times
to ensure that it will not lock into any undercuts.
Use a second mix of acrylic to build-up the required bulk for the lingual half of
the core. The resin should surround the nylon bristles projecting from the facial
core, and it should overlay the occlusal aspect of the facial core.
Use garnet discs and carbide burs to shape the axial contours and occlusal planes
of the lingual core. The core should now resemble a tooth preparation for a full
crown.
Use inlay wax to touch up any voids in the acrylic pattern. Margins should be well
adapted and axial surfaces should be free from undercuts.
After the lingual half is invested and cast, finishing is done with abrasive discs
and rubber wheels.
57
The two halves of the dowel core are assembled in the working cast to ensure that
they will fit together in the tooth.
The two piece dowel -core is now ready to be cemented in the tooth to rebuild it
for placement of the final restoration. The facial half will be cemented first
following immediately by the lingual half .On a mandibular tooth the mesial
would be first, followed by the distal.
Cut a v-shaped cement vent down the length of each dowel to assist complete seating
and the prevention of damaging stresses. The cemented dowel-core is now ready for
completion. The finish line is touched up with a chamfer diamond to provide space for
the bulk of metal adjacent to the acute margin in the final crown. The margin of the final
restoration will be placed on solid tooth structure to provide a marginal seal and to
provide a band of reinforcing metal apical to the core
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CAUSES FOR FAILURE OF METAL POST SYSTEM
The failure of post retained crowns has been documented in several studies as-
- Secondary caries
- Periradicular pathosis
- Periodontal disease
- Post dislodgement
- Cement failure
- Post- core separation
- Crown -core separation
- Loss of crown retention
- Corrosion of metallic posts
- Core fracture
- Post distortion
- Root fracture
59
60
Loss of retention of the post due to inadequate length
Bending at the post core interface
Fracture at post core interface
Loss of retention of the post due cementation failure
Loss of final restoration
Fracture of the tooth
PREFABRICATED DOWELS AND CORES
Prefabricated dowels and core combinations are an appropriate choice for most clinical
situations, particularly for posterior teeth. Though there are many variations, most
systems contain preformed metallic dowel's corresponding to the instrumentation used in
refining the dowel space.
1. Prefabricated Precision Plastic Dowel
a. Parallel b. Tapered
2. Prefabricated Dowel Cast core.
3. Prefabricated Dowel Composite resin core.
4. Prefabricated Parallel Threaded (Pretapped) Dowel.
5. Parallel Self-Threading Dowel.
6. Tapered Self-Threading Dowel.
7. Amalgam Pin core.
8. Composite resin Pin core.
PREFABRICATED PRECISION PLASTIC DOWEL
The fabricated precision plastic dowel forms part of a system in which the dowel
is designed to fit a canal space shaped by a specific instrument of matching size and
configuration. This differ from the custom dowel core because the canal is prepared to fit
the dowel rather than a pattern being made as an impression of the internal aspect of the
tooth. Precision plastic dowels are available in two configurations:
Parallel
Tapered.
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PRECISION PARALLEL PLASTIC DOWEL
Parallel dowels exhibit superior retention: studies have found them to be 1.9 times,
3.3 times, and 4.5 times as retentive as prefabricated tapered dowels of equal length. If
the surface is. serrated, retention will be improved even more.
Para post
Para Post is a prefabricated
precision serrated surface with a parallel sided
geometry. It is designed to be used with one or
more parallel pins set in dentin peripheral to
the canal. The pins act primarily as
antirotational features, although they may add
some retention and resistance to dowel cores
which are lacking those qualities because of tooth size or morphology. Conditions that
permit the use of a serrated parallel plastic dowel pattern include a fairly bulky root and a
canal, which is essentially straight. Because a parallel dowel does not follow the natural
taper of most roots, it may not be possible to choose a pattern and drill for every tooth.
The dowel picked must be large enough to leave an adequate thickness of dentin at the
apical end. If the coronal portion of the canal has been enlarged excessively, a small
dowel may fit too loosely, and a larger dowel may cause insufficient tooth structure to be
left in the apical portion.
In considering a tooth for restoration with this system, it is also necessary to
evaluate the tooth structure available for pin placement. If there is insufficient bulk to
accommodate pins, keyways can be prepared in the walls of the canals.
The most important factor in the retention of a precision parallel dowel, as with
any dowel, is length. Since no part of the dowel preparation developed by the standard
Para Post drill is rounded over or tapered, the dowel space tends to come closer at its
apical extension. An assessment of the length of the dowel space should take this into
account. The dowel should be at least as long as the clinical crown of the tooth, or as long
as possible without encroaching on the apical 4 mm of the endodontic filling
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Color coded plastic posts are available in diameters of:
1.25 mm (red)
1.50 mm (black).
1.75 mm (green)
Diameters of 0.9 mm and 1.0 mm can also be obtained. There is a paralleling jig for each
of the diameters to be used in conjunction with a 0.7 m Paramax drill. Plastic pins are
used for an impression if the indirect technique is employed, and iridoplatinum pins are
used in the direct technique for the wax pattern and casting done
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PRECISION TAPERED PLASTIC DOWEL
Most of the precision plastic dowel systems, which are marketed today, are
tapered, with the taper ranging from 1.10 to 6.2°. Some authors advocate the use of a
taper because it more nearly approximates the tapered configuration of roots, thereby
lessening the chance of a lateral perforation during dowel preparation.
To match the tapered plastic pattern to the dowel preparation with accuracy, it may
be necessary to cut a little length from the small end of the pattern, or reinstrument the
canal to enlarge it slightly, depending on whether the dowel is too loose of too tight. This
must be done with great care, comparing the depth of the dowel preparation and the
length of the dowel pattern. Other wise, it is possible to wedge a tapered dowel into the
canal, making contact with its walls short of full seating of the dowel. The operator may
misinterpret the slight 'tug back' that he feels as a manifestation of an accurate fit.
The use of a tapered precision plastic dowel with a matched reamer of same size
obviates the need for relining the dowel in the canal when the dowel core is fabricated.
The most commonly used tapered plastic dowel are:
a. Endowel System.
b. P-D Posts.
c. Coloroma kit.
d. Calibrated Instrumentation kit.
ENDOWEL SYSTEM
This system has smooth dowel patterns that are matched to hand instruments i.e
the standardized endodontic files and reamers. Therefore, they exhibit 1.1 ° taper of
standardized endodontic instruments. The dowels are available in eight sizes.
Size 1 - 70 (0.7 - 0.9 mm)
Size 2 -80 (0.8 - 1.0 mm)
Size 3 - 90 (0.9 - 1.1 mm)
Size 4 - 100 (1.0 - 1.2 mm)
Size 5 - 110 (1.1 - 1.3 mm)
Size 6 - 120 (1.2 - 1.4 mm)
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Size 7 - 130 (1.3 - 1.5 mm)
Size 8 - 140 (1.4 - 1.6 mm)
In each pair of numbers, the first designates diameter at the tip, while the second
represents the diameter 10-mm from the tip.
P-D POSTS
These are smooth sided plastic dowel patterns with a uniform convergence angle of 1.6°.
The dowel space is prepared with reamer of like taper and diameter. Each reamer has an
adjustable sliding metal stop that is held in place with a set screw. The patterns are
available in six sizes.
Size 1 - 0.9 - 1.3 mm
Size 2- 1.1 -1.5 mm
Size 3 - 1.3 - 1.7 mm
Size 4 - 1.5 - 1.9 mm
Size 5 - 1.7 - 2.1 mm
Size 6 - 1.9 - 2.3 mm.
COLOROMA KIT
There are five sizes of patterns in the Coloroma kit. The smooth sided dowel
patterns are actually a combination of tapered and parallel sided, with the tapered portion
increasing in length from 5 mm of the smallest dowel to 9 mm on the largest. The tapered
portion has a convergence angle of 6.2°. The dowel preparations are accomplished with a
color coded engine reamer of a matching size, which is tapered near the tip and parallel
sided adjacent to the shank.
Size 1 - 0.8 mm - 1.3 mm
Size 2 - 0.9 mm - 1.4 mm
Size 3 - 1.0 mm -1.6 mm
Size 4 - 1.0 mm - 1.8 mm
Size 5 - 1.1 mm - 2.0 mm
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THE CALIBRATED.INSTRUMENTATION (C.I) KIT
This kit consists of three rotary instruments. The dowel preparation is begun with
a bibevel twist drill. When the initial channel has been prepared, it is enlarged with a
pointed reamer. The final diameter and taper is achieved with a tapered fissure bur whose
size and taper match those of dowel pattern. The smooth sided patterns have a taper of
2.60 and they are available in two sizes.
Size 1 - 1.0 mm -1.3 mm
Size 2 - 1.2 mm - 1.6 mm
The two numbers in each set indicate the diameter at the tip and 10 mm from the
tip. There is a separate set of instruments for each dowel size. To match the tapered
plastic pattern to dowel preparation with accuracy, it may be necessary to cut a little
length from the small end of the pattern, or reinstrument the canal to enlarge it slightly
depending on whether the dowel is too loose or too tight.
PREFABRICATED METAL DOWEL-CAST CORE
Another approach to the fabrication of dowel cores has been one in which a
precision made prefabricated dowel is matched in size to a bur or hand reamer. After the
dowel preparation is completed, the prefabricated dowel is fit in the canal. A core is then
made of resin or wax by the direct or indirect technique. The metal dowel and its core
pattern are invested, and the core is burned out.
Then the core is cast in metal.
The use of a prefabricated metal dowel with a cast core offers the advantage of
having part of the dowel core already completed before the procedure is even begun. It
has also been promoted because of the superior strength of a wrought or drawn dowel
compared with a cast one56, especially when the dowel is less than 1.5 mm in diameter.
The prefabricated dowels have been made of a variety of materials including gold,
gold-platinum-palladium, iridoplatinum, platinized wire, nickel-cobalt-chromium and
stainless steel. The core can be fabricated by the direct or the indirect technique.
The commonly used system is the Endopost which utilizes a noble metal smooth
tapered dowel which is matched to the standard used endodontic hand f1les and reamers.
The Endopost system utilizes a noble metal dowel which exhibit the slight taper of the
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standardized endodontic instruments. It is available in eight sizes which matches the size
of the endodontic files
Size 1 - No. 70 (0.7 - 0.9 mm)
Size 2 - No. 80 (0.8 - 1.0 mm)
Size 3 - No. 90 (0.9 -1.1 mm)
Size 4 - No. 100 (1.0 - 1.2 mm)
Size 5 - No. 110 (1.1 -1.3 mm)
Size 6 No. 120 (1.2 - 1.4 mm)
Size 7- No. 130 (1.3 - 1.5 mm)
Size 8 No 140 (1.4 - 1.6 mm)
A resin core is fabricated around the incisal end of the prefabricated dowel which extend
from the tooth. The dowel can also be used for making an impression of the dowel in
order to fabricate the core indirectly.
PREFABRICATED DOWEL/COMPOSITE RESIN CORE
Perhaps the simplest and most efficient method for the fabrication of a dowel core
restoration is the composite resin core in combination with a prefabricated stainless steel
dowel core. The entire procedure from completion of the endodontic obturation through
the finished crown preparation, can be accomplished in a single appointment.
This system can be used succesfully in a wide range of clinical situations. At one
extreme, this type of dowel has been shown to significantly strengthen teeth with no
coronal destruction other than the endodontic access preparation. At the other end of the
spectrum, the prefabricated dowel/ composite core can be used to restore both anterior
and posterior teeth that have little or no intact coronal tooth structure.
Composite resin is easily and quickly placed as a core material, and it has the
added advantage of being completely polymerized within minutes, allowing work on the
core preparation to progress immediately. Preparations on amalgam cores, on the hand,
often must be delayed until a subsequent appointment. In addition, the resin requires less
bulk of core material, making it the material of choice for anterior teeth where there is
often minimal space around the dowel.
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The prefabricated dowel composite core is adequate for the restoration of single
anterior tooth. However, most anterior bridge abutments should have cast dowel-cores.
On molars with excessive destruction of coronal tooth structure or with very deep finish
lines, amalgam may be the material of choice rather than the composite resin core.
The dowel portion of the dowel composite resin core acts to resist any lateral
forces placed on the crown. Care is taken to extend the finished lines for the final
restoration well below the composite resin core. When this is done, the crown will grasp
the tooth, creating a 'ferrule' effect to resist any vertical forces. Auxiliary pins are used
routinely to resist any rotational forces placed on the restoration. In addition, there is
some evidence that pins embedded in core material across a tooth may have a 'buttressing
effect' and resist splitting forces on the root.
The prefabricated dowel composite core can also be used to restore a previously
crowned tooth that has been endodontically treated. The head of the dowel is trimmed to
fit within the confines of the access preparation and the dowel is cemented. The space
around the head is then restored with amalgam or composite.
The prefabricated dowel systems used are:
1. CI (Calibrated instrument) kit
2. Coloroma kit.
3. P.D Crownpost sytem.
4. Para Post system.
5. BCH system.
6. Ellman Nubond Fast posts.
CALIBRATED INSTRUMENT (C.I) KIT
This kit consists of three rotary instruments. The dowel preparation - is begun with
a bibevel twist drill. When the initial channel has been prepared, it is enlarged with a
pointed reamer. The final diameter and taper is achieved with a tapered fissure bur whose
size and taper match those of dowel pattern. The corrugated stainless steel dowels have a
taper of 2.60 and they are available in two sizes.
Size 1 - 1.0 mm -1.4 mm
Size 2 - 1.2 mm -1.7 mm
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The two numbers in each set indicate the diameter at the tip and 10 mm from the
tip. There is separate set of instruments for each dowel size.
COLOROMA KIT
Coloroma dowels were meant to use for fabricating temporary crowns, but they
can be used with auxiliary pins and composite resin cores. There are five sizes of patterns
in the coloroma kit. The smooth sided dowel patterns are actually a combination of
tapered and parallel sided, with the tapered portion increasing in length from 5 mm of the
smallest dowel to 9 mm on the largest. The tapered portion has a convergence angle of
6.2°. The dowel preparations is accomplished with a color coded engine reamer of a
matching size, which is tapered near the tip and parallel sided adjacent to the shank.
Size 1 - 0.8 mm - 1.3 mm
Size 2 - 0.9 mm -1.4 mm
Size 3 - 1.0 mm -1.6 mm
Size 4 - 1.0 mm -1.8 mm
Size 5 - 1.1 mm - 2.0 mm
P-D CROWN POSTS
These are stainless steel serrated dowel patterns with a uniform convergence angle
of 1.6°. The dowel space is prepared with reamer of like taper and diameter. Each reamer
has an adjustable sliding metal stop that is held in place with a set screw.
The patterns are available in six sizes.
Size 1 - 0.9 - 1.3 mm
Size 2 - 1.1 - 1.5 mm
Size 3 -7 1.3 -- 1.7 mm
Size 4 - 1.5 -1.9 mm
Size 5 -7 1.7 - 2.1 mm
Size 6 -7 1.9 - 2.3 mm.
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PARA POST SYSTEM
This is a serrated, parallel sided, stainless steel dowel which is used with a large
color coded twist drill of matching size. The dowels are available in five diameters:
Size 1 -7 0.9 mm.
Size 2 -7 1.0 mm.
Size 3 -7 1.25 mm.
Size 4 -7 1.50 mm.
Size 5 -7 1.75 mm.
Auxiliary pin holes for minim pins are placed in the root face with a. 0.5 mm
Kodex drill. Para Post is also available in a tapered end parallel sided dowel.
BCH SYSTEM
This system is comprised of two or three lengths in each of five diameters, for a
total of 14 sizes. They are meant to be used with peso reamers and come in the following
diameters:
Type I -7 0.8mm
Type II -7 1.0 mm
Type III -7 1.2 mm
The dowel are serrated and parallel sided, with tapered tips and a round button on
the occlusal end.
ELLMAN NUBOND FAST POSTS
These are serrated stainless steel posts with a 1.6° taper. The canal is prepared with
tapered reamers of matching sizes. There are Six Sizes:
Size I -7 0.9 - 1.2mm.
Size II -7 1.1 - 1.4 mm.
Size III -7 1.3 - 1.6 mm.
Size IV -7 1.5 -1.8 mm.
Size V -7 1.7 - 2.1 mm.
Size VI -7 1.9 - 2.3 mm
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THREADED DOWELS
PARALLEL THREADED DOWEL (PRETAPPED)
This dowel employs threads on its parallel sides for retention and it is inserted into
a canal whose walls are prethreaded with a special tap. It differs from other types of
dowels, because it is not passively inserted into the canal and held in place entirely by the
cement. Whether this threaded dowel is retained by mechanical interaction, or simply by
increasing the surface area two or threefold, it demonstrates superior retention to other
types of dowels. It was found to be 2 to 3.4 times as retentive as parallel serrated dowels
in one study, and 5 times as retentive in another.
Threaded dowels are not without controversy, however. Concern has been
expressed over increasing the potential of root fracture by threading dowels into the
canal. The stresses generated by threaded dowels are greater than those generated by
dowels retained by cement alone. However, mechanical testing has shown that when the
tap is used properly, fracture cannot be induced. Frequent cleaning of the tap is essential
to reduce stress and prevent resultant root fracture.
The commonly used parallel threaded dowels (pretapped) are:
Crown anchor.
Kurer fin lock
Kurer Crown Saver
CROWN ANCHOR
The original crown anchor consists of a stainless steel threaded shank (dowel)
with a slotted machine brass head (core). The canal is enlarged with an elongated engine
reamer, and its orifice is countersunk with a root facer. A tap is then used to thread the
canal for insertion of the anchor.
KURER FIN LOCK
The Kurer fin lock utilizes a threaded 'root face fin' or lock nut to snug against the
countersunk root face. A narrow collar near the slotted end serves as additional retention
for the composite resin core, which will be, added after cementation of the anchor.
71
KURER CROWN SAVER
The Kurer crown saver is s simple threaded dowel that has neither a head nor a
lock nut, and therefore, does not require the use of a root facing instrument. It consists of
a parallel threaded dowel, which is cemented, in the canal and serves as the retention for
a composite resin build up.
PARALLEL SELF THREADING DOWEL
This system offers a retentive device, which is intermediate between the stainless
steel dowel composite resin core and the pretapped parallel threaded crown anchor. The
retention afforded by this type of dowel, whose threads are widely separated and
shallow, is 94% greater than that of serrated stainless steel post of the same size. The
self threading anchor is 17% to 45% less retentive than similar sizes of pretapped
threaded anchors.
As these dowels utilize threads for much of its retention, it is capable of
producing stress in the root. Continuing to thread the anchor after resistance is
encountered could result in root fracture or stripping of the threads. If the dowel apex is
allowed to engage the supporting tooth structure, high apical stresses are generated. High
stress concentrations will develop in the coronal portion of the root if the coronal flanges
of the head come in contact with the root face. In order to avoid these problems, it is
recommended that the dowel be reversed or 'backed off a half turn when slight resistance
to threading is felt during cementation.
RADIX ANCHOR
The Radix anchor utilizes threads for much of its retention. They are made in three
diameters (dowel size exclusive of threads):
Type I - 1.1 mm
Type II -1.35 mm
Type III - 1.6 mm
The anchors consists of a low prof1le retentive,
spiral head with five rows of fms or lamellae which retain
the composite resin core that is built around it. The
72
shallow threaded spiral on the coronal 60% of the dowel is interrupted by four cement
vents which run the length of the dowel. The anchor drives the wrench used for threading
the dowel into the canal, has four prongs firmly engaging four slots in the sides of the
head. The Radix Anchor works best in teeth whose clinical crowns have some length and
volume.
TAPERED SELF THREADING DOWEL
This style of dowel has been in use for over 50 years. It is the simplest of all
threaded dowels. The use of this type of dowel is the prime example of use of the root
canal as the ultimate pin hole. An amalgam or composite resin core is usually fabricated
around the dowel after it is cemented. Because of its dowel size and the bulky head, self
threading dowels are generally restricted to use in molars.
It is frequently used on teeth with a minimum of coronal tooth structure and multiple
divergent canals. The non-parallel relationship adds to it the retentive qualities of the self
threading dowel. Its most obvious advantage is that dowel core can be placed in a single
appointment.
The tapered self threading dowel is simple and easy to use. The fact that it engages
dentin with its threads unquestionably provides excellent retention. However, this type of
dowel also produces high stress concentrations, with its wedge like action producing
stress concentrations more severe than those seen in other types of threaded dowels.
Translated into practical terms, there is a danger of cracking a root. The danger of root
fracture is more acute when excessive torque is applied, or when the dowel is over
twisted. Torqure required to seat the dowel increases with diameter, but dowel length
seems to exert no influence. Larger diameter dowels have been observed to cause root
fractures, especially in teeth with ovoid canals. Dowels which are oversized for their
prepared canal also represent a hazard to the tooth. A dowel that is too large compresses
the dentin and increases the risk of root fracture.
Durney and Rosen found that the torque required to insert a tapered, self threading
dowel was approximately one fourth of the torque needed to fracture a root
experimentally. They suggested that these dowels should be turned slowly and delicately
without leverage. This would seem to be an adequate safety margin, but clinically it has
73
not always proven to be so. It may simply be that this type of dowel has been used in too
many poorly selected weak roots by careless operators. Whatever the cause, the
recommendation has been made that tapered, self threading dowels be passively
cemented in slightly over sized canals. In a slight modification of that technique,
Tidmarsh has suggested that a dowel with a 'snug, sliding fit' be cemented, engaging the
threads no more than a single turn during seating.
Tapered self threading dowels have been implicated in corrosion which could
result in root fracture. Rud and OmnelP54 examined 468 teeth with vertical or oblique
fractures and concluded that 72% of the fractures resulted from corrosion. It was
theorized that galvanic reactions caused the formation of corrosive products that fractured
the teeth. It is also possible that the teeth were fractured at the time of insertion, or
subsequently, with the fracture remaining undetected for a ling time. The fracture
however minute would permit the free passage of saliva and / or serum into contact with
the dowel and crown, causing corrosion products to be formed after the fracture.
Nonetheless, it is recommended that the dowel be examined prior to insertion.
Confirm that the electroplated gold surface is still intact, protecting the brass body which
is 60% copper and 40% zinc. Further, that portion of the dowel to be placed in the canal
should not be cut or prepared. Derand38 recommends that the core be placed during the
same appointment at which the dowel is cemented. This will prevent the cement around
the dowel from being exposed to the fluids of the oral cavity for any prolonged period.
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DENTATUS SCREW POST
The Dentatus screw post is the most commonly used of this style of dowel. It is
marketed in a stainless steel and gold plated brass dowel (60% copper and 40% zinc).
Dentatus screw posts are available in six diameters:
DI 1.0 mm
D II 1.2 mm
D III 1.3 mm
DIV 1.5mm
D V 1.6 mm
D VI 1.8 mm
There are four lengths of dowels:
L I - 7.8 mm, L II -9.3 mm, L III - 11.8 mm, L IV - 14.2 mm
The head of each screw post is square, with two
seating wrenches. One wrench is designed to fit
internally into the head of the dowel to allow placement
of the dowel in tight areas. It also permits insertion of a
dowel whose head shape and size have been altered. A
second wrench fits over the head of the dowel. It is
useful on severely broken down teeth in which the
dowel head is unaltered.
An amalgam core or composite resin core can
be placed over the dowels. The dowel head should
not be too close to the outer perimeter of the
projected axial contours of the prepared core.
Neither, should they be closer than 2 - 2.5 mm from
the opposing occlusion. They should be altered, if
necessary. and the space between the two heads should also allow bulk of core material.
75
CORE
The core consists of restorative material placed in the coronal area of a tooth. This
material replaces carious, fractured, or otherwise missing coronal structure and retains the
final crown.
The core is anchored to the tooth by extending into the coronal aspect of the canal
or through the endodontic post. The attachment between tooth, post and core is
mechanical, chemical or both as the core and post are usually fabricated of different
materials.
The remaining tooth structure can also be altered to enhance retention of the core.
Although, pins, grooves and channels can be placed in the dentin, these modifications all
increase the core retention and resistance to rotation at the expense of the tooth structure.
In most cases the irregular nature of the residual, coronal tooth structure and the normal
morphology of the pulp chamber and canal orifices eliminate the need for these tooth
alterations. Using restorative materials that bond to tooth structure enhances retention and
resistance without necessitating the removal of valuable dentin. Therefore, if additional
retentive or antirotation form for the core is deemed necessary, dentin removal should be
kept to a minimum.
Core materials: Requirements:
1. Stability in wet environment
2. Ease of manipulation
3. Rapid, hard set for immediate crown preparation
4. Natural tooth color
5. High compressive strength
6. High tensile strength
7. High fracture toughness
8. Low plastic deformation
9. Inert (no corrosion)
10. Cariostatic properties
11. Biocompatibility
76
12. Inexpensiveness.
Materials used: 1. Cast gold
2. Amalgam
3. Composite resin
4. Glass ionomer
5. RMGIC
77
Alternative pre fabricated post and core systems utilizing materials available:
Quintessence International 1998, 29: 305-312
Application of selected criteria (Biomechanical) to evaluate core materials for pre
fabricated post and core systems (Q.I. 1998; 29: 305-312)
78
Ease of use Setting time Strength
Resin compositeAmalgam
Glass ionomer
Resin compositeGlass ionomer
Amalgam
AmalgamResin compositeGlass ionomer
Dimensional stability
Microleakage Bonding mechanism
AmalgamGlass ionomer
Resin composite
AmalgamGlass ionomer
Resin composite
Resin compositeGlass ionomer
Amalgam
CORE MATERIAL
CAST GOLD: Type III and Type IV cast gold alloys are used.
Advantages:
1. Offers good strength
2. Resistance to leakage derived from luting agent
3. Does not absorb water
4. close to that of dentin.
5. Cast gold buildups require post for retention and substantial degree of coronal
destruction to be used.
Disadvantages:
1. Time consuming
2. Expensive
AMALGAM: Material of choice in high stress situations
Advantages:
1. Simple to use
2. Radiopaque
3. High compressive strength & fracture toughness in both static & dynamic loading.
4. High contrasting color to the tooth
5. Dimensionally stable
6. Antimicrobial
7. Acceptable long-term performance as documented in the literature.
Disadvantages:
1. High thermal conductivity
2. High co-efficient of thermal expansion than the tooth
3. Does not adhere to the tooth substance
4. Low early strength –requires separate appointment for crown preparation
5. Dark color of Amalgam – potential to lower the value of all – ceramic restorations
causing a gray halo at the gingival margin.
79
COMPOSITE RESIN:Possess satisfactory physical properties for core buildup material.
Advantages:
1. Reliable bond to tooth structure
2. Command set nature – allows immediate crown preparation
3. Adequate fracture toughness & compressive strength in static & dynamic loading.
Disadvantages:
1. High coefficient of thermal expansion – potential for microleakage
2. Not dimensionally stable in wet environment
3. Water sorption – absorbs water = core expands, composite dries = core shrinks.
GLASS IONOMER CEMENT: used in posterior teeth with more than 50% of tooth
structure remaining.
Advantages:
1. Adhesion
2. Fluoride release
3. Co-efficient of thermal expansion similar to tooth
4. Radiopaque
5. Contrasting color to tooth
Disadvantages:
1. Low compressive strength and fracture toughness
2. Low flexural strengths.
RESIN MODIFIED GLASS IONOMER CEMENT: Newest available core material.
Advantages:
1. Adhesion
2. Fluoride release
3. Easy to manipulate
4. Intermediate physical properties – lie between GIC and composite resin.
Disadvantages:
Low flexural strength and fracture toughness
Volume in stability – severe expansion during initial setting reaction.
80
CEMENTATION
Dowel and core materials have changed much in recent years. The ability to bond
to dentin has significantly expanded. The options available to the restorative dentist has
altered every phase of dowel and core restoration. Dowel can be cemented with:
Zinc phosphate cement
Polycarboxylate cement.
Glass ionomer cement.
Resin Composite cements
Resin modified Glass Ionomer
The general cementation procedures for insertion of dowel and core restorations
are very similar, regardless of cement type. Once mixed, the cement is delivered to the
dowel space with a lentulo spiral, to ensure that all walls are coated. At the same time, the
dowel and core are coated with a thin layer of cement. Retention is greatest when both
the dowel and the root are coated, rather than either alone. The restoration should slide
slowly and easily into place with light finger pressure. Excess cement must escape
coronally as the dowel nearly fills the dowel space. Once the restoration is fully seated, it
should remain untouched until the cement has passively set.
LUTING AGENTS
ZINC PHOSPHATE CEMENT
Zinc phosphate cement sets by an acid base reaction initiated on mixing a powder
composed of 90% ZnO and 10% MgO with a liquid that consists of approximately 67%
phosphoric acid buffered with aluminum and zinc. The water content (33%) is significant
because it controls the ionization of the acid, which in turn influences the rate of the
setting reaction. This is important to the clinician because an uncapped liquid bottle will
permit loss of water resulting in retarded set. Water evaporation should be suspected if
the liquid appears cloudy on dispensing.
Zinc phosphate cement has been in use for more than 90 years. If" properly mixed,
the cement exhibits adequate mm thickness to comply with ADA specification No 8. The
mixing technique is critical in developing the optimal cement and should be completed
on a cool slab, over a wide area, to incorporate small increments of powder into the liquid
81
for approximately "1 minute and 30 seconds. The post should be seated promptly after
mixing the cement, because the viscosity of most cement is known to increase rapidly
with time. Optimal crown seating requires proper mixing and a constant heavy
cementation force. The cement strength is almost linearly dependent on the powder:
liquid ratio; thus, the more powder the better strength. Compressive (80to 110 Mpa) and
tensile strengths (5 to 7Mpa) of properly mixed zinc phosphate are adequate to resist
masticatory stress. The set cement is extremely stiff and exhibits a high modulus of
elasticity of 13 Gpa, which permits the cement to resist elastic deformation in regions of
high masticatory stress or in long span prostheses.
Zinc phosphate does not chemically bond to any substrate and provides a retentive
seal by mechanical means only. Thus, the taper, length and surface area of the tooth
preparation are critical to its success. Several studies have demonstrated significant linear
penetration of silver nitrate from the external margin along the restoration tooth interface
after crown cementation. Microleakage, aggravated by degradation in oral fluids and an
initial low setting pH, may affect its biocompatibility in clinical use. Of utmost
importance, however, is the long clinical track record of this cement. Its inherent stability
was reported in a study that analyzed the chemical structure of zinc phosphate cement
samples obtained from 27 fixed prostheses that were in clinical service from 2 to 43
years. Whereas a fresh, 48 hours - old cement contained mainly amorphous zinc
phosphate and unreacted zinc' oxide and phosphoric acid, older cements were found to be
profoundly chemically stable over time. The proven reliability of this cement validates its
use in long term luting of well- fitting, prefabricated and cast posts, metal inlays, onlays,
crowns, FPDs, and aluminous all ceramic crowns to tooth structure, amalgam, composite
or glass ionomer core buildups.
POLYCARBOXYLATECEMENTS
Polycarboxylate cements, first introduced in the 1960s, set by a fast acid - base
reaction that occurs when zinc oxide and magnesium oxide powders are rapidly
incorporated into a viscous solution of high molecular weight polyacrylic acid.
Fortunately, these cements exhibit thixotropic or pseudoplastic behavior where an
apparently viscous mix flows readily under pressure. However, they exhibit an early,
82
rapid increase in f1lm thickness that may impede the proper seating of a casting. During
setting, the cement passes through a rubbery stage and at this time, it should remain
undisturbed to prevent it from being pulled away from under the margins.
Polycarboxylate cements have lower compressive (55 to 85Mpa) and higher
tensile (8 to 12Mpa) strengths than zinc phosphate. Polycarboxylate cements are
hydrophilic and capable of wetting dentinal surfaces. They exhibit chemical adhesion to
tooth structure through the interaction of free carboxylic acid groups with calcium. One
should hypothesize that a truly adhesive cement would be less susceptible to
microleakage, but 2 studies have shown a similar degree of marginal leakage for both
polycarboxylate and zinc phosphate cements. In addition, their adhesion to tooth structure
is reported to be of minor importance for the retention of well- fitting cast restorations,
because polycarboxylates exhibit interfacial adhesive failures at the cement - metal
interface.
Cohesive failures, within the cement, were noted only with film thicknesses greater than
250/J.m.
After hardening, polycarboxylate cements exhibit significantly greater plastic
deformation than zinc phosphate cement; thus, the cement is not well suited for use in
regions of high masticatory stress or in the cementation of long span prostheses. Some
formulations contain stannous fluoride, but its release of fluoride ion is small when
compared with glass ionomer cement. Perhaps the strongest clinical merit of this cement
lies in its reported biocompatibility with the dental pulp, which could be due to a rapid
rise in pH after mixing and / or lack of tubular penetration from the large and poorly
dissociated polyacrylic acid molecule. This cement is warranted for the cementation of
single metal units in low stress areas on sensitive teeth.
GLASS IONOMER CEMENT
This cement type is a descendant of the silicate and polycarboxylate cements and was
introduced for clinical use as a luting agent in the early 1908. The cement sets by 'and
acid base reaction between aluminum fluorosilicate glass particles and a liquid, which
consists of copolymers of relatively weak polyalkenoic acids, including itaconic, maleic
and tricarboxylic. These acids can also be , freeze- dried and incorporated into the
83
powder component, which is then mixed with water to reconstitute the acid, tartaric acid
is also present to provide flow and increase the working time. These cements are thought
to adhere to tooth structure by formation of ionic bonds at the tooth cement interface as a
result of chelation of the carboxy groups in the acid with the calcium and / or phosphoric
ions in the apatite of enamel and dentin. They exhibit higher compressive strengths (90
t0230Mpa) than zinc phosphate cement.
Several studies have reported decreased microleakage over nonadhesive type cements.
However, some in vitro studies have not confirmed superior retentive potential for glass
ionomer when compared with zinc phosphate. Cements are available in hand mixed and
capsulated forms. Hand-mixed cements often contain more bubbles of larger diameter,
which may contributed to a decrease in strength. The compressive strength of glass
ionomer is higher than polycarboxylate and zinc phosphate cements. However, their
modulus of elasticity is lower than zinc phosphate cements; than there is potential for
elastic deformation areas of high masticatory stress.
Previous studies have reported that glass ionomer cements posses low f11m
thickness and maintain relatively constant viscosity for a short time after mixing. This
results in improved seaating of cast restorations compared with zinc phosphate cement.
However, low film thickness may not be completely advantageous, because microcracks
have been attributed to thin cement layers where a homogenous distribution of curing
stresses cannot occur.
The main drawbacks of this cement are tits well-documented susceptibility to moisture
attack and subsequent solubility if exposed to water during the initial setting period. Early
exposure to water and saliva contamination has been shown to significantly decrease the
ultimate hardness of zinc phosphate and glass ionomer cements. If the marginal
adaptation of the restoration is poor, water sorption and dissolution may result in
dislodgment of the restoration. Application of petroleum jelly around the crown margin
immediately after placement of the crown has been suggested as a way to prevent
moisture contamination of the unset cement. The cement is also susceptible to
dehydration, leading to cohesive failure from microcrack formation when teeth were not
kept fully hydrated. It was suspected that cracking occurred because of stress
84
concentrations as water was drawn out of the setting cement. This finding underscores the
need to maintain some level of dentin hydration during cementation procedures.
The initial low setting pH of glass ionomer was reported and implicated as a cause
for postcementation sensitivity. Subsequent studies have disputed this implication. Pulpal
injury and postcementation hypersensitivity are most likely multifactorial and caused
irritation from cavity preparation, thin cement mix ill junction with excessive hydraulic
force, and microleakagc. Clinical evaluation of restorations cemented with zinc
phosphate and glass ionomer cements has reported minimal postoperative
hypersensitivity and a good prognosis for abutments.
The long term fluoride release and uptake of glass ionomer restoratives has been
reported and the cariostatic activity of glass ionomer cements has been proposed.
However, although fluoride is released, the small "quantity of cement at the margin may
not have any significant clinical therapeutic value as a cariostatic agent. Glass ionomer
cements are indicated for cementing cast restorations in the same manner as zinc
phosphate cement.
RESIN COMPOSITE CEMENT
Resin cements are variations of filled BIS-GMA resin and
other methacrylates. They polymerize through chemically initiated
mechanisms, photopolymerization, or a combination of both. They
are available in various shades and opacities and their chemistry
allows them to adhere to many dental substrates. Adhesion to
enamel occurs through the micromechanical interlocking of resin
to the hydroxyapatit.e crystals and rods of etched enamel.
Adhesion bf resin to dentin is more complex, involving penetration of hydrophilic
monomers through a collagen layer overlying partially demineralized apatite of etched
dentin.
Dentin "adhesion" is obtained by inf1ltration of resin into etched dentin, producing
a micromechanical interlock will partially demineralized dentin, which underlies the
hybrid layer or resin interdiffusion zone. Adhesion to dentin with resins requires multiple
steps, beginning with the application of an acid or dentin conditioner to remove the smear
85
layer, smear plugs, open and widen tubules and demineralize the top 2 to 51mm of
dentin. The acid dissolve and extracts the apatite mineral phase that normally covers
the collagen fibers of the dentin matrix and opens 20 to 30 nrn channels around the
collagen fibers. These channels provide an opportunity to achieve mechanical retention
of subsequently placed hydrophilic adhesive monomers. An optimal 2 to 5 micro miter
zone of demineralization has been described with a 15 seconds application of
conditioner. Prolonged application of acids to dentin results in a deeper demineralized
zone that resists subsequent resin infiltration. If complete infiltration of the collagen by
the primer does not occur, the collagen at the deeper demineralized zone will be left
unprotected and subjected to future hydrolysis and final breakdown. After
demineralization, the primer, a wetting agent such as HEMA is applied. The agent is
bifunctional, in that it is both hydrophilic, which enables a bond to dentin and
hydrophobic, which enables a bond to the adhesive. The primer is applied in multiple
coats to a moist dental surface. Multiple coats are required to replace the water in the
damp dentin with the resin monomers and to carry the adhesive material into the tubules.
The primer is gently dried so as not to disturb the collagen network but to remove any
remaining organic solvents or water that could obstruct the ,contact of the resin adhesive
with the primer. Adhesive resin is then applied to the "primed" surface to stabilize the
primer-infiltrated demineralized dentin and to penetrate into the dentinal tubules. Subtle
differences in the amount of cross-linkage and penetration between commercial
adhesives can occur.
The use of dentin bonding agents has somewhat compensated for the
polymerization shrinkage evident with all resin composites.
However, the rigidity of cast restoration of the resin adhesive and the stresses generated
within the shrinkage cement vary with cement type, thickness, and cavity geometry.
These stresses may be substantial enough to form gaps between the cement and the tooth.
Adhesion to tooth structure benefits from a thin resin layer, if the bond can overcome
polymerization stresses. Studies have reported that the bond -strength of resin composite
luting agent to etched ceramic may exceed the bond to dentin when new generation
dentin bonding agents are used. Although polymerization shrinkage continues to be an
impediment to complete dentinal adhesion for this type of cement, the adhesion obtained
86
is sufficient to warrant the use of these agents for cementing crowns short, tapered
preparations with non-ideal angles convergence.
Resin composite resin bond chemically to resin composite restorative materials
and to silanated porcelain. Resin adhesives increase the fracture resistance of ceramic
materials that can be etched and silanated. Resin cements also demonstrate good bond
strengths to sandblasted base metal alloys as a result of micromechanical retention, and
the 4-META resin cements show strong adhesion as a result of chemical interaction of
the resin with an oxide layer on the metal surface. Noble alloys may be electroplated with
tin to increase the surface area for bonding and perhaps enable a chemical bond to the
deposited tin oxide.
Most resin adhesives are filled 50% to 70% by weight, with glass ionomer or
silica; they exhibit high compressive strength, resistance to tensile fatigue, and are
virtually insoluble in the oral environment. The filler also contributes to improved
marginal wear resistance in comparison to hybrid resin and glass ionomer cements;
however, a high filler content increases viscosity, which in turn reduces their flow and
increases film thickness. The ability to seat restoration with the resin cements has been
investigated and, in some situations, cement film thickness has been found to be greater
than other classes of cements. Cement film thickness can be reduced with the use of
electromallet or ultrasonic devices.
However, as with polycarboxylate cements, the bond strength of resin composite
adhesives to metal has been found to increase, up to a point, with a concomitant increase
in cement film thickness.
Some resin composite cements contain ytterbium trifluoride and are capable of
some fluoride release. Other formulation includes a barium fluorosilicate filler and claim
additional fluoride release. This may imply that the cements offer cariostatic potential.
However, significant sustained fluoride release of resin composite materials or real
clinical therapeutic value has yet to be described. The amount of fluoride release needed
to inhibit enamel demineralization has not been defined and controlled clinical trials have
not been proven the cariostatic efficacy of fluoride – releasing materials.
87
The ability to adhere to multiple substrates, high length, insolubility in the oral
environment, and shade-matching potential has made resin composite cements the
adhesive of choice for esthetic type restorations. Adhesion to noble metals can be
achieved but requires tin-plating. Resin cements are. useful when the preparation lacks
optimal retention and resistance forms. Proper use requires multiple steps that are
technique sensitive.
Inspite of its various advantages, resin adhesives are even more technique
sensitive during its usage inside the root canal. The uniform etching of the root canal
space and the removal of the etch ant have to be done meticulously. Moreover, the effect
of the etchant on the underlying apical gutta percha has not been studied properly. A
predictable bond strength is questionable until a uniform layer of the adhesive is applied
throughout the root canal space. One of the most common failures in this system is
inadequate polymerization of the resin.
Several studies have been conducted to evaluate the retention of dowels luted with
resin cement in teeth that were obturated with gutta percha using a eugenol sealer or a
calcium hydroxide sealer. Eugenol (2-methoxy-4- allyphenol), an obtundent to pulpal
tissues, is found in many dental products including dental sealers. Many clinicians prefer
sealers containing eugenol, possibly because of its antimicrobial activity that could
improve the clinical success of the endodontic therapy. However, numerous studies have
shown the inhibiting effect of eugenol on the free radical addition polymerization
reaction of chemically cured composite resin. Inhibition occurs, because eugenol reacts
with free radicals associated with resin polymerization. The use of a eugenol containing
sealer may also affect resin cement polymerization when a dowel and core is luted. It has
been shown that eugenol can reduce the bond strength of resin to dentin and negatively
influence the retention of a dowel in a prepared dowel space.
In a study by Tjan et al on the effect of eugenol containing endodontic sealer on
the retention of prefabricated dowels luted with an adhesive composite resin cement, they
found eugenol significantly reduced the retention of Para Post dowels luted with Panavia
EX composite resin cement. They also reported that canal irrigation with ethyl alcohol or
etching with phosphoric acid could assist in negating eugenol's influence, resulting in
increased bond strengths. However in this study, the eugenol containing endodontic
88
sealer liquid was introduced directly into the canal immediately before placing the dowel
and resin-luting agent. This protocol may not provide an adequate understanding of the
influence of eugenol in a clinical setting when set sealer and gutta percha are removed
from a canal during post space preparation. It has also been shown that by mechanically
cleaning a dentin surface with pumice before dentin bonding, the eugenol-based cements
have no effect on the dentin-resin bond strength. Recent studies with newer dentin
bonding systems have shown no adverse effect on the dentin bond after eugenol
contamination. Burns et al have conclusively proved that conventional endodontic
obturation using a eugenol containing or calcium hydroxide containing endodontic sealer
did not affect the retention of prefabricated stainless steel dowels luted with resin cement.
RESIN MODIFIED. GLASS IONOMER CEMENTS
This fifth class of luting agents hardens by setting reactions that lead to the
formation of a metal poly acrylate salt and a polymer. These cements harden to an acid-
base reaction between fluoroaluminosilicate glass powder and an aqueous solution of
polyalkenoic acids modified with pendant methacrylate groups, and by photo-initiated or
chemically initiated free radial polymerization of methacrylate units. Because of this
chemistry, the cements are termed resin-modified or hybrid glass ionomer.
These cements have compressive and diametral tensile strengths greater than zinc
phosphate, polycarboxylate, and some glass ionomers but less than resin composite. Their
adhesion to enamel and dentin, and their fluoride release pattern is similar to
glass ionomer cements. In addition, they also bond to resin composite. They
are more resistant to water during setting and are less soluble than glass ionomers. These
cements may have some cariostatic potential and resistance to marginal leakage. Perhaps
the biggest advantage of these types of cements is their case .of mixing and use, because
multiple bonding steps are not required. They also have adequately low film thickness.
In addition of resin has not significantly reduced dehydration of the glass ionomer
component of these cements, and dehydration shrinkage has been observed as late as 3
months after maturity. A significant disadvantage of the resin ionomers is the hydrophilic
nature of polymerization HEMA, which results in increased water sorption and
subsequent plasticity and hygroscopic expansion. This behavior is analogous to a
89
synthetic hydrogel. Although initial water sorption may compensate for polymerization
shrinkage stress,' continual water sorption has deleterious effects, Potential for
substantial dimensional change contraindicates their use with all ceramic feldspathic -
type restorations.
Manufacturers of resin ionomer cements recommend that they be used for luting metal or
porcelain fused - to- metal crowns and FPDs to tooth, amalgam, resin composite, or glass
ionomer core buildups, but their use for cementing posts in non viral teeth is questionable
because of the potential for expansion induced root fracture.
Resin ionomer cements present concern regarding biocompatibility due to the presence of
free monomer in the liquid, Although rare, dimethacrylate may elicit an allergic response
'from certain persons and careful handling by dental personnel is recommended during
mixing.
The application of desensitizing agents after tooth preparation can seal dentinal
tubules and decrease microleakage. Studies have reported that resin primers may decrease
the retention of zinc phosphate and polycarboxylate cements, but have little effect on
glass ionomer, resin composite, resin modified glass ionomer cements. It is known that
eugenol-containing materials inhibit the cross-linking of resin adhesives. While
noneugenol containing cements are recommended for luting interim restorations before
final cementation with resin adhesive cements, retention of resin modified glass ionomer
cements is not significantly affected by eugenol - containing provisional materials, as
long as the provisional cement is completely removed with a thorough prophylaxis.
90
CEMENTATION TECHNIQUE
It has important effect on the eventual retention and stress distribution of the post.
Essential to achieve a uniform, bubble free layer of cement that
distributes the stress evenly throughout the entire root canal.
Use of a lentulosprial – considered to be superior to place the cement
into the canal. It gives better spinning and spreading of the cement because of
centrifugal dispersion of the cement. It also reduces voids and increases the
contact of the cement with the walls.
During cementation – post space should be free of any residue, as it has
been reported that even a small nodule on the post surface or temporary cement
residue in the canal can generate enough force to cause root fracture during and
after post cementation.
Other possible causes of root fracture are :
Development of hydrostatic pressure in the cement
Excessive seating pressure
Excessive torque exerted by the clinician on the post during cementation.
Before cementation of the post :
1. Post space should be cleaned by a chelating agent, 17% EDTA for 30 seconds.
2. Followed by rinsing with 5.2% NaOCI (30 sec)
3. Canals should be rinsed with water and dried with paper points.
This procedure will help the post space wall to be free of root canal sealant, debris
and dentinal smear layer.
91
Treatment of the post before cementation
To enhance retention, the surface of the post can be micro-roughened before
cementation with 50-micron aluminum oxide and a micro air abrasive unit (MicroEtcher,
Danville Engineering Inc., Danville, CA) with 60 p.s.i. air pressure. Before cementation
Zinc
phosphate
Poly
carboxylate
GIC Resin
ionomer
Compomer Adhesive
resin cement
Film thickness
25 <25 <25 >25 >25
Working time
1.5-5 1.75-2.5 2.3-5 2.4 3.10 0.5-5
Setting time
5-14 6-9 6-9 2 3-7 1-15
Comp. Strength (MPA)
62-101 67-91 122-162 40-141 194-200 179-255
Elastic modulus
13.2 - 11.2 - 17 4.5-9.8
Pulp irritation
Moderate Low High High High High
Solubility High High Low Very low Very low Very low Microleakage
High Very high Low-high Very low High-to very high
Very low to low
Removed of
Easy Medium Medium Medium Medium Difficult
Retention Moderate Low-moderate
Moderate-high
Moderate-high
Moderate High
92
Venting :
Because of the intraradicular hydrostatic pressure created during cementation of the post,
a means for cement to escape must always be provided. Because virtually all
prefabricated posts have a venting mechanism incorporated in their design, this factor is
important with the custom cast post. A vent may be incorporated in the pattern before
casting or into the with a bur prior to cementation.
93
PROVISIONAL RESTORATIONS FOR ENDODONTICALLY TREATED TEETH
A temporary restoration commonly plays an important role in the successful
restoration of a tooth. It is true that the normally essential role of pulpal protection is not
of concern in dealing with an endodontically treated tooth. Nevertheless, the temporary
restoration may be even more important to the patent receiving a dowel-core and a
crown.
Functions:-
Esthetic role
Protects the tooth from further damage
Prevents migration of adjacent contacting teeth
Provides occlusal function
A number of different crown formers and dowels are used in various
combinations. Polycarbonate crowns have been relined with acrylic, as have celluloid
crown forms. Over impressions and plastic shells have used to form the outer contours of
the crown. Other types of retentive devices have included plastic dowels relined with
acrylic resin, a silicone dowel reinforced with a paper clip, metal dowels with no acrylic
lining, and a wooden match stick. Some prefabricated dowel systems have steel dowels
made specially for temporary crowns. However, they work best if the matching reamer
was used in preparing the canal for the final dowel-core.
The polycarbonate crown is well suited for the routine single crown. If the
temporary restoration involves a bridge, or unusual alignment or morphology in a single
crown, a custom plastic shell will probably provide the best result in the shortest time.
Polycarbonate Crown
The polycarbonate crown is used with a paper clip dowel to provide temporary
coverage for the endodontically treated tooth. The coronal portion of the restoration is
composed of a polycarbonate crown, relined with acrylic resin.
94
Initially, a crown is chosen that has dimensions compatible with the space it will
occupy. In most cases, the crown will not adapt around the existing root without
modification. Excess length is removed form the gingival margin of the crown, while the
incisal area is left intact. This process is continued until the crown is adapted reasonably
well to the gingival finish line, with the incisal edge in the proper position relative to the
adjacent teeth.
A section of paper clip made of heavy gauge wire is placed into the canal to its
full depth. A felt tip pen mark is placed 2-4 mm. above the remaining coronal tooth
structure. The length of wire extending into the crown will be
dictated by the length of the crown. The longer the exposed piece
of paper clip, the better its retention in the acrylic resin in the
crown.
Using a separating disc, cut the length of paper clip..
Some small notches can be placed in the wire at this time to
assist in retention of the resin. Place a bend near the end of the
wire. When embedded in the temporary crown, this bend will
prevent the dowel from pulling out and rotating. Try the trimmed
dowel in the canal and confirm that the polycarbonate crown will have room to seat
without binding on the wire.
The root face is lightly lubricated with petrolatum to prevent any acrylic resin
from sticking to the tooth during polymerization.
A thin mix of temporary acrylic resin is placed on the root face around the orifice
of the canal. Avoid placing any resin deep into the canal space itself, since this can make
the crown difficult to remove. Insert the paper clip dowel into the canal. Fill the
polycarbonate crown with the same mix of acrylic resin. Eliminate any voids in the
material before placing it on the tooth. Seat the crown and confirm that it is in the proper
position relative to the adjacent teeth. Excess acrylic can be removed with an explorer to
make trimming easier. As the material reaches a doughy consistency, the crown should
be pumped in and out of the tooth several times to avoid being locked in place during
polymerization.
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The pin-temporary crown can be placed in hot water to speed polymerization.
Prior to trimming and contouring, it is helpful to mark the margin on the inside of the
crown with a sharp pencil. The temporary crown is trimmed with sandpaper discs. The
polycarbonate crown will frequently be overcontoured in the gingival one-third. Special
attention should be given to properly shaping the restoration and making any needed
adjustments in occlusion. Perforating the polycarbonate crown is not a problem because
there is an underlying bulk of acrylic. The temporary crown is first polished with fine
pumice and then with a high-lustre denture polish.
Temporary cement should be placed only in the coronal portion of the restoration.
Avoid getting cement in the canal space. A zinc oxide-eugenol cement mixed with an
equal part of petrolatum is acceptable. Seat the pin-temporary crown and hold it in place
with firm finger pressure until the cement is set. Carefully clean the excess cement from
around the margins.
Clear Plastic Shell
Another method for constructing a pin-temporary crown involves the use of a
clear plastic shell. While the shell can be shaped by a vacuum forming machine, it is
more easily and economically adapted by using silicone putty. Begin by placing the putty
into an unperforated stock metal impression tray.
Cut a sheet of coping material in half and place it in a wire frame, shiny side
down. The plastic material is slowly heated over a flame until it sags. If it is translucent,
it should become clear as it softens. If the material is the clear variety, it should be heated
until it begins to smoke slightly.
The heated coping material is quickly carried to the diagnostic cast. If the tooth to
be restored is badly broken down, it should have been waxed to an acceptable contour
and duplicated in plaster or stone. A duplicate cast is necessary because the hot plastic
would melt the wax if it were placed on the original cast.
The tray loaded with putty is placed over the plastic and firmly seated on the cast.
Compressed air can be blown on the shell to speed cooling. After about 30 seconds, the
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tray and the silicone putty are removed. A well adapted plastic shell covers the cast. The
coping material is removed from the cast and trimmed with scissors.
The finished shell should extend at least one tooth in either direction from the
tooth being restored. It should also be trimmed to extend no more than 2-3 mm, beyond
the gingival sulcus. A paper clip is prepared in the same manner described previously.
The end is bent to aid retention in the temporary crown. The shell is filled with temporary
acrylic resin. Before seating the shell, examine the acrylic from the outside to make sure
there are no obvious voids or bubbles. They can be eliminated much more easily at this
time than they can be filled in later. If the mold appears adequately filled, the shell can be
seated. Make sure that it is in the proper position by firmly pressing on the incisal edges
of the adjacent teeth. Avoid pushing on the tooth being restored because the coping
material may over seat and distort the temporary crown.
When the material reaches a doughy consistency, remove the shell and separate it
from the temporary crown. If it is left in place too long, it can be locked in place in the
canal or between adjacent teeth.
Trim off as much flash as possible with scissors while the acrylic is still doughy.
Reseat the crown on the tooth and remove it. Drop the temporary crown in a bowl of hot
water to speed polymerization. The temporary crown is contoured with a sandpaper disc.
Check the occlusion and adjust as necessary. Polish the crown first with pumice and then
with high luster denture polish. Cementation procedure is same as that described for
polycarbonate.
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RECENT ADVANCES
B. Non Metallic posts:
1. Carbon fibre post:
The carbon fiber posts were introduced in 1990 following research undertaken by Duret
and associates in France. They consist of continuous, unidirectional, pyrolytic carbon /
graphite fibres reinforced in an epoxy resin matrix with 64% carbon. Parallel sided,
smooth post, wider coronally and tapers towards the apex.
Types of Carbon Fibre Posts
1. Composi post : (RTD, France)
2. Endopost; (RTD, France)
3.Carbonite system; (Switzerland, kent)
4. Mirafit carbon; (Hager Werken, Germany)
ADVANTAGES:
1. Better strength
2. High flexibility
3. Easy retrievability
4. Better redistribution of stresses
5. High fatigue resistance
DISADVANTAGES:
1. Aesthetics– the black colour of post has a negative effect on the final aesthetic result of
all ceramic crown
2. Poor adhesion to composite resins as the heat processed carbon fibre posts have little
free resin available for chemical reaction causing failure of post / cement interfere.
3. Lack of radioopacity- New advances with second generation tooth coloured posts,
were introduced to improve this aesthetic challenge. These are termed as Silica fibres
posts / Glass fibre posts / Quartz fibre post.
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COMPOSIPOST SYSTEM
'The Composipost system (RTD, Meylan, France), comprising a carbon fiber post,
a composite core material, and a low viscosity Bis-GMA bonding resin, has been recently
introduced to the market with the manufacturers claiming several interesting advantages
over existing products:
1. Complete post/ core and cement system in one kit.
2. Homogenous mechanical and chemical bonding of all components, which serves to
reinforce the tooth
3. Carbon fiber post has a Young's modulus approximating that of natural teeth, which
results in decreased stress concentration and therefore an increased longevity of the
restoration.
Sidoli et al assessed the compressive strength values of endodontically teeth
restored with the Composipost post and core system with teeth restored with Parapost
stainless steel posts and composite core; and cast gold post and core. The results
indicated:
a. When tested with a single angle compressive load, teeth restored with the Composipost
post and core system exhibited significantly inferior stress values at failure when
compared with the other systems.
b. The mode of failure of the Composipost and core system, with angled compressive
load testing, however, was more favorable to the remaining tooth structure.
One potential advantage of a fractured Composipost system, compared with a
metallic post, is the relative ease of removal from the posthole by conventional rotary
instruments.' This factor, combined with the less destructive nature of tooth damage,
would allow the possibility of salvage and repreparation with the minimum of complex
treatment. A further advantage is the elimination of corrosion when a carbon post is used
in combination with a composite core, compared with some metallic post and core
systems that exhibit corrosion.
The Composipost dowel is made of equally stretched and aligned carbon fibers,
solidly attached to a special matrix of epoxy resin. The interface between the carbon
filaments and the matrix is an organic composition. The carbon fibers by exerting
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uniform tension on the filaments impart high strength to the posts. The composipost
dowel has a cylindrical shape, and it tapers into two conical shaped seating faces of
different diameters for stability. The height of the conical seating is 1 mm. All the posts
have the same overall length of 22 mm and are available in the following diameters; .
Upper Shank Diameter : 1.4 mm, 1.8mm and 2.1 mm. lower Shank Diameter : 1.0 mm,
1.2 mm and 1.4 mm.
Composipost are passive and are designed to be used with a bonding technique.
The recommended core material is Resilient composite, a BISGMA resin filled with short
glass fibers. Boston
.
Post or sticky post resin cements were used previously for bonding. They are now placed
by a new bonding system, which is a radio opaque composite dual cure cement associated
with a primer such as Allbond 2. It provides high bond strength and a hybrid layer,
furthermore clinical procedures for Composipost are 1c% time consuming and expensive
than the conventional procedures for cast metal posts.
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TOOTH COLOURED POSTS
Major disadvantage of metal posts and CFP’s is their dark colour, which
adversely affects the natural appearance of the restored tooth. To overcome this
disadvantage tooth coloured posts were developed.
Silica fibre posts:
1. glass fiber posts
2. quartz fiber posts
Glass Fiber Posts
Glass fibers have a lower elastic modulus than carbon / graphite fibers. These posts can
be made of different types of glasses.
i. Electrical glass (E-glass) - is the most commonly used glass type in which the
amorphous phase is a mixture of Silicon di Oxide, Calcium Oxide, Barium Oxide,
A1uminium Oxide and some other oxides of alkali metals.
ii. High strength glass(S-glass) - is also amorphous but differs in composition.
TYPES OF GLASS FIBRE POSTS;
1.Snow Post – (Carbotech, France)
2. Parapost fibre white: (Cottene / Whaledent)
3. Glassix : (Harald Nordin Sa, Switzerland)
4.. Mirafit white: (Hager Werken, Germany)
5. Luscent anchor: (Dentatus, Sweden)
6. Fibre kor : ( Jeneric / Pentron, USA)
7.FRC postec : ( Ivoclar / Vivadent )
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FRC Postec
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Glassix post system
QUARTZ FIBRE POSTS:
Additionally glass fiber post can also be made of quartz fibers. Quartz is pure silica in
crystallized form. It is an inert material with a low co-efficient of thermal expansion
(CTE).
TYPES OF QUARTZ FIBRE POSTS:
I. Aestheti post: (RTD, France)
Ii. Aestheti plus post: (RTD, France)
Iii. Light post: (RTD, France)
iv. Style post: (Metalor technologies, London)
Advantages
1. Flex with the tooth structure
2. Easy to retrieve, if retreatment is required
3. Aesthetic compatibility
4. Greater fracture resistance
5. Useful in polymerization by transmitting tight through the post.
Physical properties of these posts is similar to carbon fibre posts.
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ALL - CERAMIC POSTS AND CORES
In 1989, Kwiatkowski and Gellerl described the clinical application of glass-
ceramic posts and cores (Dicor, Dentsply) and in 1991, Kern introduced posts and cores
made of glass-inf1ltrated aluminum oxide ceramic In 1995, Pissis144, proposed a
monobloc technique for the fabrication of a post and core and a crown as a single
component made out of glass ceramic material In 1994 and 1995, Sandhaus and Pasche
and others introduced prefabricated zirconia ceramic endodontic posts to restorative
dentistry
The major advantage of an all ceramic post and core is its dentin like shade. The
positive contribution of the dentin shade ceramic core is related to the deeper diffusion
and absorption of the transmitted light in the ceramic core mass. An all-ceramic
restoration transmits a certain percentage of the incident light to the ceramic core and
post on which it has been placed. Thus with all ceramic posts and cores, the color of the
final restoration will be derived from an internal shade similar to the optical behavior of
the natural teeth.
In addition, a ceramic post does not reflect intensively through thin gingival tissues, and
it provides an essential depth of translucency in the cervical root areas. All ceramic posts
and cores, as metal free constructions, provide an excellent biocompatibility and do not
exhibit galvanic corrosion.
Relatively low fracture strength and fracture toughness are the main obstacles for
an extended use of conventional dental ceramics as post and core materials.
There are few research data on the fracture strength of all ceramic posts and cores, and
for clinical behavior no long term clinical data are provided in the literature.
Apart from the fracture strength, the fracture toughness of a ceramic material seems to be
more predictive of its failure rate.
High toughness ceramics, such as the glass int1ltrated alumina ceramic In-Ceram and the
dense sintered alumina ceramic Procera (Nobel Bio care), show a 3 to 6 times higher
flexural strength and fracture toughness than do conventional feldspathic and glass
ceramics. Contemporary zirconia powder technology contributes to the fabrication of
new biocompatible ceramic materials with improved mechanical properties, ie., further
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Slip castingbefore sintering
Sintered post and core
Glass infiltered post & core
increased flexural strength and fracture toughness. Therefore, zirconium oxide ceramic
seems to be a very promising material for the fabrication of all ceramic posts and cores.
SLIP - CASTING TECHNIQUE
The fabrication of all ceramic posts and cores by use of the slip casting technique
was described by Kern and Knode in 1991. With this technique, the core buildup and the
post are made in 1 piece from the aluminum oxide ceramic material, In Ceram. Because
of the limited fracture strength and the unknown long-term clinical prognosis: of In-
Ceram as a post and core material, this method should be used only in wide root canals
without a crucial reduction of the circumferential dentin structure.
The preparation of the root canal is similar to the preparation for a metal post and
core. Possible undercuts are eliminated manually with standardized reamers during the
root canal preparation. At the coronal end of the root canal, a small inlay cavity is
prepared to prevent rotation of the finished post and core.
The tooth preparation for an all ceramic crown requires a 90° shoulder with a rounded
internal angle or a deep chamfer with a width of 1.0 to 1.2 mm circumferentially. As the
preparation is finished, all line angles should be slightly tapered.
A prefabricated plastic or metal post is placed in the root canal and a high
precision impression is taken. After the master cast is set, the tooth die is sectioned and
the preparation margins are exposed and marked with ink. The die is duplicated, and a
second die is cast with the special In-Ceram plaster. The duplicated die is used for
formation of the post during the slip casting. After its hardening and removal from the
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impression, the bottom of the second die is ground with a carbide bur until a tiny opening
appears. During the slip casting, this hole serves as an external relief that prevents air
impaction in the slip mass. In addition, it is a reliable indicator of the slip injection's
completion. Finally, horizontal and vertical sections, which must not reach the root canal
are made on the die with diamond disks.
As an alternative method, the working die can be separated into 2 pieces by the
insertion and a slight rotation of a sharp knife in a drain channel cut along the die. These
2 parts are glued together, again with cyanoacrylate adhesive. The adhesive is burned out
when the furnace is heated to 100 degree centigrade, so that no force is exerted by the
shrinking die at higher temperatures.
Wax up of the core is then made on the master die, and; the occlusal clearance is
confirmed on an articulator. Diameter wax sprue is attached to the -incisal edge of the
core, providing later the entrance for the slip injection. Two putty silicon molds of the
wax up and the master cast are fitted together with internal retentive undercuts. After the
removal of the wax up, the die of the special In Ceram plaster is adapted between, and
finally the 2 silicon molds are joined with rubber rings. With this procedure, a void space,
previously occupied by the core wax up and the sprue, is provided for the slip injection.
The alumina slip is mixed and ultrasonically vibrated to a homogenous
consistency according to the manufacturer's instructions and then is injected through the
injection spine of the silicon mold. After the slip has dried, the core is carefully carved to
its final shape with a scalpel. One coat of Stabilizer (Vita Zahnfabrik) is applied to the
finished core. The sintering is done according to the regular firing cycle settings for the In
Ceram ceramic, as recommended by the manufacturer. After sintering, the all ceramic
post and core is fitted to the master cast. Then it is checked for possible micro-cracks by
the use of methylene blue liquid.
For the subsequent glass infiltration firing, the post and core is placed on a
platinum foil and is covered with a mixture of lanthanum - glass powder and the special
liquid supplied with the In Ceram system. The excess glass is removed with coarse grit
diamond grinding and 50 urn air abrasion. Then the all ceramic post and core is fitted
again to the master cast.
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After the fit of the all ceramic post and core is checked in the patient's tooth, the
post and core is adhesively cemented. Rubber dam is applied for moisture control. The
root canal is roughened with a diamond coated reamer and cleaned with 70% alcohol. A
self-curing dentin adhesive agent is used prior to cementation with a self curing resin
cement. If a phosphate monomer containing resin composite is used for the cementation,
the In Ceram post and core need only be sandblasted and ultrasonically cleaned in 96%
alcohol.
After the resin cement has set, the excess cement is removed by diamond grinding, and
the tooth preparation is finalized with finishing diamonds.
COPY - MILLING TECHNIQUE
Recently, the glass infiltrated alumina
ceramic, In Ceram, and its fabrication process have
been adapted to the Celay copy milling method
(Mikrona), as an alternative to the slip casting
technique. The Celay system involves a manually
guided copy milling process in which a: pre-designed
resin pattern is surface traced and copied in ceramic. The ceramic substructures are
prefabricated blanks made of presintered aluminum oxide ceramic (Celay Alumina
Blanks, Vita Zahnfabrik). In Ceram ceramic restorations made with the Celay method
present a 10% higher flexural strength (about 500 Mpa)
then do conventional In Ceram restorations.
This method can be used for inlay, onlay, veneer, and crown and bridge
framework fabrication, as well as for copy milled In Ceram posts and cores. The clinical
indications and procedures are similar to those of the conventionally slip cast posts and
cores already described.
For the copy milling technique, the resin 'pre-post and core' pattern can be made by a
direct or an indirect method. The direct method presupposes that the resin analog of the
post and core is modeled on the patient's tooth, similar to the conventional technique for
casting metal posts and cores. This intra oral method is simplified by the use of
prefabricated plastic or metal posts in combination with the appropriate root canal system
107
For the indirect method, an impression of the prepared tooth is taken and a
working cast is poured out of plaster. The resin pre post and core is modeled as in the
indirect fabrication method for metal posts- and cores. For the molding of the internal
inlay of the post and core, a light curing resin with increased viscosity (eg., Visioform,
ESPE) can be used to simplify the handling.
After the resin pre post is completed, it is mounted to the tracing chamber of the
Celay machine. The pre post is mounted vertically, so that the incisal edge of the core is
attached to a jig of the retentive device and the end of the post is connected to a pin on
top of the cup holder. Then, the resin pattern is surface traced and copied in ceramic by
synchronized grinding in the milling chamber. For a precise fit, special attention should
be paid when the internal inlay is milled. After completion of the copy milling process,
the ceramic post and core is cut off with a diamond disk; fitted to the master die, glass
infiltrated, and finished as described above.
TWO PIECE TECHNIQUE
Because the fracture strength of In Ceram posts and cores is less than that of metal
posts and cores, In Ceram posts and cores have only been recommended for wide root
canals. In cases of regular root canals (smaller than ISO 110), In Ceram ceramic does not
seem to provide a sufficient strength; for that reason, until presently, an all ceramic post
and core was not recommended for such cases. After the recent development of zirconia
ceramic posts, it became possible to combine both materials. For a 2 piece post
and core construction, a post made of yttrium oxide partially stabilized zirconia (ER
Cerapost, Brasseler) is used in conjunction with an all ceramic core made of alumina or
alumina magnesia ceramics, fabricated either by the copy milling or the slip casting
technique. The zirconia ceramic posts are commercially available in three ISO sizes (050,
090, 110) and supplement the existing ER Post system (Brasseler).
This technique is also applicable for both direct and indirect fabrication methods.
For the direct method, the root canal is prepared, and the selected zirconia ceramic post is
tried in A core is formed intra orally by adapting the light curing resin composite Celay
Tech to the inserted post. After the removal of the resin core from the post, the core is
copied in ceramic in the Celay machine. For the indirect fabrication method, an
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impression of the inserted post is taken, and a working die is cast. The core is then
formed with the light curing resin composite Celay Tech on the master cast.
Finally, it is also copied into ceramic. As an alternative to the copy milling core
fabrication, the slip casting technique can be used as described earlier, with a minor
modification. A plastic post of the ER System is inserted in the root canal of the special
In Ceram plaster die. This plastic post provides accurate space for the zirconia ceramic
post and does not cause any problems because it is burned out during the sintering firing.
After the core wax up and the two silicon molds are made, the slip is injected as
described for the slip casting technique.
A fter glass infiltration firing, the infiltrated alumina core and the zirconia post are
sand blasted and ultrasonically cleaned in 96% alcohol. For cementation, an adhesive
resin (eg., Panavia 21, Kuraray) is applied to the bonding surfaces of the post and core,
and then they are both luted to the abutment tooth. Primarily, the ceramic core is placed
on the prepared tooth and immediately afterward the post is inserted in the root canal
through the canal of the core. Finally, after setting of the luting resin, the post is
shortened at its protruding occlusal end, and the tooth preparation is finished.
When a sufficient amount of a caries - free tooth substance is available, instead of
the ceramic core buildup, a self curing resin composite buildup can also be used in
combination with a zirconia post.
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HEAT - PRESS TECHNIQUE
The heat press technique has recently found
application to an all ceramic post and core construction. It is
based on the well known IPS Empress system (Ivoclar). In
this system, a castable, pre-cerammed leucite reinforced glass
ceramic material is heated and pressed in an investment mold
after the burn out of the wax analog (lost wax technique). In
the heat press technique, a glass ceramic core (Empress
Cosmo, lvoclar) is heat pressed over a prefabricated zirconium dioxide post (Cosmo Post,
Ivoclar), and therefore both materials are fused into a solid post and core restoration.
For the root canal preparation, special reamers (Cosmo Post Set. Ivoclar) is used
so that the canal can receive a zirconia post with the appropriate diameter (1.4 or 1.7
mm). After the impression is taken and the master cast is constructed, the core wax
pattern can be molded in the laboratory. An intra oral direct method can also be employed
with the use of a self curing resin (GC Pattern, GC) after insertion of the post in the root
canal. The heat press procedure, which is identical for both methods, is followed. A 3.0
mm diameter and 6.0 to 8.0 mm long wax sprue is attached to the core with an inclination
that allows a uniform flow and expansion of the glass ceramic. At that time, the post and
core is invested in a phosphate bonded refractory die material.
The heat press procedure is performed in a specially designed furnace (IPS Empress EP
500, Ivoclar). The ceramic ingot is first heated at 1,180 degree centigrade and then is
pressed with 0.3 to 0.4 Mpa pressure under vacuum. After cooling and divestment, the
post and core, as a solid, all ceramic construction, is fitted to the master cast. Then, it is
tried in the patient's mouth and adhesively cemented as previously described.
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DIRECT METHOD FOR CERAMIC POSTS
After tooth preparation, if sufficient tooth structure remains, a ceramic post can be
placed. A prefabricated all ceramic post (Biopost) or TXP post, which is biocompatible
and has favorable mechanical properties, and can be used with a composite core.
The tooth selected for this procedure should have at least half the height of the
future crown preserved in dentin. Prepare the root canal for the post, based on
contemporary biomechanical principles using a series of specific cylindrical burs in
accordance with the manufacturer’s directions.
Select a post of suitable length and diameter with the aid of a radiograph. Sandblast the
corresponding ceramic post and cement. Complete the core reconstruction with resin and
prepare the tooth for an all- ceramic crown.
111
WOVEN-FIBRE COMPOSITE MATERIALS/ POLYETHYLENE FIBRE
MATERIALS:
The use of cold gas plasma treated, polyethylene woven
fibres embedded in conventional resin composite has been
advocated for corono radicular stabilization of pulpless teeth.
They consist of woven fibre ribbons. Used as a matrix for the
construction of direct etch – retained composite splints.
Ribbond suggested that the woven polyethylene fiber can
also
be used to construct and directly place composite post and
core.
Removal of the obturation material and a minimal amount
of dentin to facilitate insertion of the ribbon is the only
preparation required. One or more length are coated with
bonding agent, folded into a V-shape around an instrument
and then carried into the canal space to be cured.
Additional increments are then added to complete the core
build up.
Advantages
1. Compared to preformed posts, there is no additional
tooth removal after endodontic treatment. This maintains
the natural strength of the tooth.
2. Eliminates the possibility of root perforation.
3. Because it is made when the Ribbond is in a pliable state,
it conforms to the natural contours and undercuts of the
canal and provides additional mechanical retention.
4. There are no stress concentrations at the tooth-post interface.
5. The Ribbond post and core is passive and highly retentive.
Disadvantages
1. Special scissors required to cut the fibers
112
LIGHT – TRANSMITTING POSTS
Translucent posts (light post and luscent archor) have been introduced in order to allow
the use of light cured luting agents. This can facilitate cement
placement and evaluation of post seating prior to setting.
The original purpose of these posts was to provide a means of
reconstituting roots with overly flared canals caused by caries
or excessive endodontic preparation, the aim being to achieve
union between the remaining, dentine and a light cured
composite, thereby restoring the lost bulk and original
strength of the root.
The plastic posts require a diameter greater than 1.5mm to
achieve complete curing to a depth of over 7mm. The relative
ability of the glass fibre versions to transmit light has not yet
been reported.
TWIN LUSCENT ANCHORS :
This innovative design is visible assurance against accidental
debonding of adhesive and resin-core materials. The slim mid-section
creates a “physical choke”. The vent groove eliminates air resin entrapment
and prevents rotational dislocation. It all adds upto a winning combination of
light transmission, attractive esthetics and twice the retention.
Light transmitting : Effectively polymerizes composite within
the deep confines of canals.
Esthetics : Eliminates shadows at the gingival, root and crown
interface as well as through thin-laminate composite restorations.
113
Reflects the surrounding colors and hues, compatible with natural
esthetics.
Monobloc strength : Light or dual cure composites bonds to
the fiberglass reinforced anchors creating a cohesive, very strong
foundation for restorations.
Narrow radial midsection : Mechanical resistance seen in the
anchor’s midsection provides double retention against accidental
debonding of resins and restorative materials.
Double-end alternatives : The anchor cone shaped-end can be
placed in deeper and narrower canals without excess removal of dentin or
canal wall. The parallel end can be alternatively placed into long, wider
canals of teeth. The parallel canals can be refined with drills, used in
parallel canal post techniques.
Longitudinal vent-groove: Eliminates trapped air bubbles
causing porosity, for completely filling the canal. Additionally, the vent-
groove creates an antirotational resistance in the surrounding
polymerized resin material.
Low modulus of elasticity (20.1 Gpa) : The Anchor’s
elasticity in the range of healthy teeth, provides safety and cohesive
resistance to impact.
Flexural Strength (579 Mpa): The Twin Anchors within the
rang of healthy teeth are outperforming metal posts.
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TWIN-LUSCENT STARTER KIT
Available in 3 diameters to fit large and very slim canals.
15 twin luscent anchors (5 of each size, small, medium, large)
3 corresponding size reamers
1 pathfinder
1 probos II router
15 forms to fit
DOUBLE TAPER POST SYSTEM (D.T POST)
The capacity of different types of post-and-core to protect the
prosthetic restoration from biomechanical failures varies greatly. Post-to-
canal adaptation represents an important element in the biomechanical
performance of the prosthetic restoration.
The new DT- Post system was designed with the purpose of providing
close canal adaptation wit minimal tooth structure removal.
The DT- Post system seem to offer a logical solution in restoring
endodontically-treated teeth. D.T. Post provides bigger taper at the coronal level.
115
A better adaptation at the coronal level increases the amount of
the fiber-epoxy high performance material, therefore, consequently
decreases the thickness of the resin cement, a lower performance
material, and reduces its polymerization total shrinkage.
D.T post combines the conservative aspect of Endo-
composipost UM apically, and the greater size of the Composipost
coronally.
The post is fabricated with a prestressed glass fiber system due to
which it can resist more than 1,00,00,000 cycles in a fatigue resistance test,
in which the closest competition could only take 1,73,000 cycles.
TRANSILLUMINATING LUMINEX POST SYSTEM :
A user friendly, single office visit solution for restoring
compromised thin-willed roots with strong adhesive materials.
All too often, fragile, thin-walled teeth present major restorative
problems : cast posts or extractions were often the only alternative.
But today, there is a user friendly, single office visit solution to
this problem.
The clear light transmitting posts polymerize light-cured
composites within the entire root canal. After curing, the LUMINEX post
is removed, leaving a ready canal for a corresponding classic post.
Reinfroced root strength : Light-cured composites internally
reinforce the root structure providing maximum sheer load support and
retention.
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Improved control : Light-curing composites are easy to control,
more adaptive, and safer than auto-cured composites that may
prematurely harden.
Centered canal position : The luminex post technique centers
the canal and forms a selected sized, full length parallel sided canal for
corresponding dentatus classic metal posts.
Superior aesthetics : The light-cured composite inside the canal
masks metal posts with a reflective tooth colored foundation for modern
restorations.
Technique versatility : Luminex smooth and grooved posts may
be also used as an impression and castable post pattern in the direct and
indicrect fabrication of posts.
Superior delivery system : Selection of Luminex and metal
posts in all sizes along with corresponding reamers and components are
packaged in the refillable, easy to use dispenser.
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STRESS ANALYSIS FOR POST AND CORE
Restoration of the pulpless tooth is critical for
successful endodontic therapy. The nature of force existing
in teeth and surrounding tissues has been a subject to
investigation by dental researcher for a century or more. As
technique has developed for increasingly radical
restorations of damaged teeth, interest has naturally
expanded to include stresses induced in reconstructed teeth
in function.
Knowledge of the kinds of stress normal dental structures must withstand and
therefore restored structures should withstand is of obvious value. The ability to perform
stress analysis on reconstructed teeth is of substantial importance in optional prosthesis
designs.
Stress analysis methods used:
1. Photoelastic stress analysis
2. Finite element stress analysis
118
REMOVAL OF EXISTING POSTS
Occasionally the dentist is confronted with an endodontically treated tooth with a
poor prognosis because of the fractured dowel. Retreatement with a post and core cannot
be attempted unless the fractured post is removed.
The techniques & instruments currently available to remove a post & core include
1. Masserann technique
2. the Little giant post puller
3. Kanematsu dowel removing plier
4. S.S White post extractor
5. post puller
6. Gonon post removing system
7. Saca Pino post extractor
8. Ultrsonics
Masserann Procedure :
The appropriate size trepan bur is determined by a
gauge supplied in the kit. The trepan bur is turned by hand,
cutting a small trench around the post. After proceeding from
one third to one half the way down the post, the trepan bur is
replaced with the next smaller size, which will grip the end of
the post to lift it out of the canal. If necessary, the trepans can
be used to extend to the bottom of the post for easy
removal.
Advantages :
1) It is simple,
2) Little heat is generated,
3) There is no danger of pushing fragments further into the root, and
119
4) Excessive forces are eliminated with little chance of perforation or splitting the
root.
This technique may make it possible to save strategic teeth that other wise might
be lost.
Little giant post puller
This instrument can remove a post safely because it grasp the dowel firmly for
removal while the studs of the instrument support the tooth. However, there are
conditions in which the instrument cannot be applied. These include
1. A discrepancy in the level of the remaining tooth structures, particularly on the
mesial and distal portion.
2. Thin mesial and distal remaining tooth structure and brittleness of endodontically
treated teeth.
3. Remaining tooth structure is too small for the studs to support.
Kanematsu dowel removing plier
This is applier with a modified working end thus enabling a firm grasp on the exposed
dowel. Counter rotational force is applied onto the post to facilities its removal.
SS white post extractor
This is also a modified plier in the same mode as the kanematsu dowel removing
plier.
Post puller
Warren and Gutman have described a simplified technique for post removal using a post
puller. The post and tooth are reduced to allow for attachment of the post puller. The first
set of jaws push puller are securely fasten onto the post while the second set of jaws push
away from the tooth in line with the long axis of the tooth lifting the post out of the canal.
120
The advantages of this system include conserving root structure and reducing the risk of
root fracture, root perforation and root torquing.
Gonon post removal technique :
Pierre Machtou, Philippe Sarfati and Anna Genevieve presented the Gonon post
removing system for removing posts from the root canals prior to endodontic retreatment.
The principle of this instrument is comparable to a cork screw. The post and the
tooth are separated by pitting the tooth against the post and creating enough force to
overcome the bond.
1) The first step is to free the head of the post from the coronal tooth structure. All
restorations including crowns must be removed.
Circumferential prereduction of the core may be achieved using a tapered
diamond bur at high speed.
2) An ultrasound device is useful to vibrate the post and disintegrate the cement.
3) In order to facilitate the centering of the trephine, a special bur included in the
Gonon kit is used to taper the protruding head of the post.
4) The high strength trephine is used to bore and gauge the protruding post to the
exact size of a corresponding mandrel which is specially manufactured to thread
the post.
5) Before the mandrel is screwed onto the post, three rings are positioned onto its
shank. This acts to cushion the mandrel and to spread the forces onto the root
surface as the post is being extracted.
6) The extracting pliers are fixed on the mandrel and the jaws of the pliers are
expanded by tightening the knurled knob. This procedure will separate the post
from the tooth quickly and safely facilitating endodontic retreatment.
Sometimes the space between the adjacent teeth is smaller than the width of the jaws.
This problem may be resolved by slipping a hollow tube included in the package into the
“long” threaded mandrel.
121
Saca pino post extractor
The design of the saca pino extractor may be likened to that fan extraction forceps. The
angled head permits access to every tooth in the mouth. The jaws of the instrument grip
the post securely so that the instrument does not sip as the post is being unseated. The
dentist has directed control over the amount of force used to grip the core and remove the
post, which reduces the danger of root fracture.
Ultrasound
Ultrasound had been advocated as an aid in the removal of fractured files, silver cones
and posts from the root canal. Its application in post removal is related to the fact that
ultrasonic waves are transmitted through the post and break the cement seal, thus
facilitating removal.
Advantage
1. conserving the remaining tooth structure
2. avoiding root perforation
3. minimizing fracture risks
4. saves time
122
REVIEW OF LITERATURE
Fleming Isidor et al evaluated the fracture resistance of bovine teeth with prefabricated
carbon fiber posts. The results of this study were compared to a previous study conducted
by the authors that had been conducted under similar condition with prefabricated parallel
sided posts (Para post) and tapered, individually cast post. The failure rates of the 2 types
of post from the previous study i.e parallel sided post and tapered, individually cast post
were significantly higher than those of the carbon fiber19.
Robert W Loney et al studied the effect of load angulation on the fracture resistance of
the teeth restored with cast post and core and crowns. They subjected the prepared
specimens to the loads at 110, 130 and 150 to the long axis of the tooth. Mean failure
loads increased as load angle approached parallelism to the long axis of the teeth. The
results showed significant difference in fracture resistance of post restored teeth can
occur as a result of load angle. (IJP 1995 8, 247-251)58.
Lennart Mollersten et al studied the comparison of strengths of five post and core
systems for root filled teeth, Composi post, carbon fiber dowels and gold alloy posts and
cores, for vital teeth glass ionomer cement with threaded parapulpal retention pins, resin
composite with threaded parapulpal retention pins and gold alloy with parallel parapulpal
pins were tested. They concluded that Composi post and cores and cast gold posts and
cores were equivalent in strength and did not vary significantly from gold cores
constructed on vital teeth. (Q.I 2002, 33,,140-144)42.
D.G Purton and J.A Payne compared carbon fiber and stainless steel root canal posts.
They concluded that carbon fiber post appeared to have adequate rigidity for their
designed purpose. The bond strength of the resin composite cores to the carbon fiber
posts was significantly less than that of the stainless steel post. (Q.I 1996,27,93-97)53.
Erik Asmussen et al studied stiffness, elastic limit and strength of newer types of
endodontic posts. They concluded that ceramic posts were very stiff and strong, with no
123
plastic behavior. The titanium post was as strong as, but less stiff than the ceramic posts.
Composi post had the lowest values of stiffness, elastic limit and strength of the post
investigated. (JOD 1999, 27,275-258)17.
William A.Saupe et el compared the fracture resistance between morphologic dowel and
cores and a resin reinforced dowel system in the intraradicular restoration o f structurally
compromised roots. The resistance to a stimulated masticatory load of a resin re-inforced
post and core system was significantly greater than that of a morphologic post and core
procedure80.
Bret I.Cohen et al determined the fracture load of four core material supported by five
post designs. They concluded that for all post Tytin silver amalgam and Ti-core material
were significantly stronger than ketac-silver and G-C Miracle mix material.(JPD
1996;76,487-95)11.
Giovanni E. Sidoli et al (1997)2- Compared failure characteristics of Composi post core
system, Stainless steel post and composite core, and cast gold post and core. The
Composi post system exhibited inferior strength properties in comparison to other post
and core systems24.
Arturo Martinez-Insua et al (1998)3 Compared the fracture resistance of pulpless teeth
restored with a cast post and core and carbon fiber post with a composite core. The
results revealed that teeth restored with cast gold posts and core recorded a higher
fracture threshold than teeth restored with carbon fiber post5.
John.P.Dean et al (1998) evaluated the influence of endodontic and restorative
procedures on fracture resistance of teeth and compared the incidence of root fracture in
teeth with clinical crowns removed that were restored with three different types of post
and a composite core build-up. They concluded that tooth with post and composite build
ups failed at significantly lower forces than teeth in which crowns had not been removed.
124
Teeth restored with stainless steel posts demonstrated 50% incidence of root fracture,
where as those restored with carbon fiber post and composite core had no root fracture14.
C.J Cormier et al (2001)- Evaluated the fracture resistance, failure mode and
retrievability of six post systems at four simulated clinical stages of tooth restoration.
The titanium parapost had greater resistance to failure and caused greatest number of
unfavourable root fracture than other post systems. The fiber posts were an improvement
over conventional posts in terms of root fractures and retrievability of posts14.
Chirstophe G. Raygot et al (2001)- Evaluated fracture resistance and mode of fracture
of endodontically treated incisors restored with cast post and core, prefabricated stainless
steel post and carbon fiber reinforced composite post systems. The use of carbon fiber-
reinforced composite posts did not change the fracture resistance or the failure mode of
endodontically treated teeth compared to the use of metallic post12.
Paulo. C. A. Maccarl et al (2003)- Evaluated the role of composition of prefabricated
esthetic posts in fracture resistance of endodontically treated teeth. Post systems utilized
were Astheti-Post, FiberKor Post and Cosmo Post. They concluded that the fracture
strength of Cosmo Post was significantly lower than that of the other posts. Ceramic
posts, carbon-fiber prefabricated esthetic post provided endodontically treated with
higher fracture resistance.
Yun-Hsin-Hu et al (2003)-Evaluated the fracture resistance of endodontically treated
anterior teeth restored with four post and core systems.
The results showed no significant difference in the failure loads among different post and
core systems but root fracture was detected in the group restored with ceramic
post and resin composite cores.
125
N VELMURUGAN, A P ARAMESHW ARAN (2004) - Described single sitting chair
side procedure for fabrication of custom made resin post and core. They concluded that
fabricating a custom-made resin post and core is easier, time saving, economical,
esthetically compatible and bonds to the root dentin resulting in a single monobloc80.
126
CONCLUSION:
Endodontic therapy is an essential component of the practice of restorative
dentistry at the close of the 20th century. Dental practice and its success are inextricably
tied to the quality of the restoration. Before making a treatment decision, the restorative
dentist must evaluate the quality of endodontic treatment, the periodontal support
available, and the status of the remaining tooth structure. The subsequent restoration for
the endodontically treated tooth is function of the remaining tooth structure, the shape
and configuration of the canals, and the functional and esthetic demands on the tooth.
Arriving at the best solution is a complex process, affected by many different
variables, including available post systems and restorative foundation materials.
Although there are additional experimental laboratory data on which to base a restorative
decision, long-term controlled clinical data are not yet available. Restoring the
endodontically treated tooth remains one of the most challenging problems facing the
restorative dentist. An uncomplicated and systematic decision making process, based on
universally accepted philosophy and techniques, is necessary to maximize chances for a
successful restorative outcome.
If certain basic principles are followed in the restorative of endodontically treated
teeth, it is possible to achieve high levels of clinical success with most of the current
restorative systems. These principles include:
Avoid bacterial contamination of the root-canal system.
Provide cuspal coverage for posterior teeth.
Preserve radicular and coronal tooth structure.
Use posts with adequate strength in thin diameters
Provide adequate post length for retention
Maximize resistance from including an adequate ferrule
Use posts that are retrievable.
127
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