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3.
PRINCIPLES OF TOOTH PREPARATION
PROCEDURES
FABRICATION OF POST
PROVISIONAL RESTORATION
INVESTING AND CASTING
POST REMOVAL SYSTEM
CONCLUSION
BIBLIOGRAPHY
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4. INTRODUCTION
Initially only extraction
From past 20 – 30 years, increased interest in restoring.
It is well known that with proper endodontic treatment and
adequate restoration, pulpless teeth can serve indefinitely as
an integral part of the dental apparatus, provided the
supporting structures are not compromised.
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5. From the time of Pierre Fauchard till date a wide range of
materials, techniques and designs have been described to
restore endodontically treated teeth.
However, there is no clear consensus regarding an ideal
system, this is because each tooth presents with a unique
requirement.
A thorough understanding of the proper use of posts and
cores will enable clinicians of today to provide an optimum
restoration that uniquely balances between maximizing
retention of the tooth while minimizing the risk of failure.
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6. HISTORY AND EVOLUTION
Restoration of endodontically treated tooth by a post to retain a
crown dates back more than 250 years.
In 1747, Pierre Fauchard a French dentist used “Tenons”
which were metal posts (Gold or silver) into the roots of teeth to
retain bridges. He used heat softened adhesive called MASTIC.
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7. Later wood replaced metal as the post material, and the “Pivot
Crown”, a wooden post fitted to an artificial crown and to the
root canal became popular. But they led to repeated episodes of
swelling and pain.
In mid 1800 –Dr.F.H.Clark – developed a “spring loaded
dowel” a retentive device consisting of a metal tube in the
canal and a split metal dowel which was inserted into it. They
also had channels for continuous suppuration from the
underlying tissues.
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8. G.V. Black developed porcelain fused to metal crown held in by
a screw inserted into a canal filled with gold foil.
In 1878 , the “Richmond Crown”, a single piece post-retained
crown with a porcelain facing was engineered to function as a
bridge retainer.
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9. During the 1930s, the custom cast post and core was developed
to replace the one piece post crowns, because of their drawback
of using in diverging roots and difficulty in removal and
replacement of FPD crowns.
In 1960s prefabricated posts were introduced.
1990 Duret et al described a non metallic material for the
fabrication of posts based on carbon fibres reinforcement
principle.
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13. ENDODONTIC EVALUATION
Good apical seal as revealed by radiographs.
No tenderness on percussion
No apical sensitivity
No exudate
No fistula
No active inflammation.
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14. PERIODONTAL EVALUATION
Periodontal health is critical to the long term success of teeth that
have been endodontically treated and restored.
Periodontal condition must be assessed before endodontic
treatment, and the effect of planned restoration on the attachment
apparatus must be considered.
Any structural defects of teeth should be considered that jeopardize
coronal restoration.
Extensive caries, tooth fracture, previous restoration, perforation
and external resorption can destroy tooth structure at the level of
the periodontal attachment.
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17. ESTHETIC EVALUATION
Potential esthetic complication should be investigated before
initiation of endodontic therapy.
Thin gingiva may transmit a shadow of dark root through the
tissue.
Metal or dark carbon fiber post and amalgam placed in the canal
can result in unacceptable gingival discoloration from the
underlying root.
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18. The translucency of All-ceramic crowns must be considered in
the selection of dowel and build-up materials.
Tooth colored carbon fiber glass-reinforced composite resin, or
zirconia posts can be used in esthetic areas. Similarly, tooth
colored, rather than opaque, composite core material should be
selected for esthetics.
An intact endodontically treated tooth requires critical control of
endodontic materials in the coronal third of the canal and pulp
chamber in order to maintain its color and translucency.
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19. Gutta percha discoloration can be visible in the coronal aspect
of an endodontically treated tooth and should be limited to an
apical level in the root.
Endodontic and restorative materials in these esthetically
critical cases must be selected to provide the best health service
with the minimum of esthetic compromise.
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20. TREATMENT GOALS
to maintain the coronal and apical seal of the root canal
filling material
to protect and preserve remaining tooth structure
to provide a supportive and retentive foundation for the
placement of a definite restoration
To restore function and esthetics.
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21. Post
The post is defined as a relatively rigid, metallic or non metallic
restorative material inserted into the root canal of a nonvital
tooth to aid in retention of a core component and to transmit the
forces .
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22. INDICATIONS FOR POST
To retain the restoration
To protect remaining tooth structure
Marginal integrity
To stabilize radicular fractures
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23. CONTRAINDICATIONS FOR POST
Abnormal root anatomy.
Extensive caries including root caries.
Perforations.
External resorption.
Short roots.
Dilacerated roots.
Blunderbuss canal.
Young patients with coronal fracture, with incomplete root
formation.
Patients with poor oral hygiene.
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24. Ideal requirements of post
Simple and safe.
Biocompatible.
Should support the core and crown.
Should provide resistance for stresses.
Maximum protection of root.
Adequate retention within the root.
Pleasing esthetics, when indicated.
High radiographic visibility.
Easily removable.
Less expensive.
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26. depending upon the preparation
custom made posts
pre-fabricated posts
depending upon material used
metallic posts eg; stainless steel, brass, Ni-Cr, CoCr, Ti, gold-platinum
non-metallic posts eg; composite and ceramic post.
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27. depending upon the flexibility
stiff
flexible – flexi post
depending upon the esthetics
esthetic
non-esthetic
depending upon the retention
Active –eg; flexi-post, Kurer anchor
passive – cast post, smooth tapered post, parapost
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28. depending upon the design
a. tapered
- Smooth sided posts
- Serrated posts
- threaded posts
b. parallel
- Smooth sided
- Serrated posts
- threaded post
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29. Pre-fabricated posts
Tapered, Smooth-Sided Posts
- The oldest and most widely used design.
Eg : Kerr Endopost, Mooser post and all custom-cast posts.
- least retentive of all post designs, Used low functional loads
-wedging pressure upon roots during function.
-Used when other designs are contraindicated
-self-venting and easily cemented, no Hydrostatic pressures because a
taper does not act as a piston.
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30. Tapered Posts with Self-Threading Screws
Eg : Dentatus
- More retentive……gains its retention by spreading into the
dentin as it self-threads.
- Sets up fracture lines as it “cuts” and spreads its way into the
dentin.
- The wedge configuration of the screw design is accentuated
under load when occlusal forces are added to the installation
forces described above.
.
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31. Parallel-sided Posts
ex; Whaledent posts which has three post designs: Para-Post,
Para-Post Plus, and the Unity System. All are passive, parallel,
vented posts made of either stainless steel or titanium.
- provides substantially greater retention than the smooth tapered
design. Consequently, these posts can be effectively employed in
situations where higher applied forces are expected.
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32. The Para-Post has a vertical groove cut along the length of its
serrations, allowing axial venting. This design allows cement to
escape….
Provide the most equitable distribution of masticatory forces of
all available post designs.
Avoids the wedging effect of tapered posts. The transfer of
occlusal forces of the tooth occurs via the cement layer, which
serves to buffer the forces. Together, these two factors result in
a uniform distribution of stresses in the supporting tooth.
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33. CARBON FIBRE
Introduced in 1990 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.
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35. DISADVANTAGES:
Aesthetics– the black color of post has a negative effect on the
final aesthetic result of all ceramic crown
Poor adhesion with composite causing failure of post / core
interfere.
Lack of radio opacity
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36. Zirconia posts
Compatible with all ceramic crown
Made up of tetragonal zirconium polycrystals.
High flexural strength, fracture toughness, radiopaque.
Better adhesion with composite core materials.
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37. WOVEN-FIBRE COMPOSITE MATERIALS
Use of cold glass plasma
treated polyethylene woven
fibres
embedded
in
conventional
resin
composite
Consists of woven fibre
ribbons
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38. THE CORE
The core is defined as a restorative material placed in the
coronal area of a tooth to replace the missing coronal structure.
The core is anchored to the tooth by extending into the coronal
aspect of the canal, or through the endodontic post.
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39. Ideal properties of the core material
High compressive and tensile strength.
High modulus of elasticity (rigidity).
High fracture toughness.
Dimensional stability.
Ease of manipulation.
Short setting time.
The ability to bond to both tooth and post.
Biocompatibility.
Inert (no corrosion).
Natural tooth color, when indicated.
Low plastic deformation.
Low cost.
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41. Cast core
This has been the traditional means
for restoring endodontically treated
teeth. The cast core is an integral
extension of the dowel and the cast
core and hence does not depend on
mechanical means for retention to
dowel. This construction avoids
dislodgement of the core and crown
from the dowel.
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42. Amalgam core
Dental amalgam is a traditional core build-up material with a
long history of clinical success
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43. Advantages
Not especially technique sensitive.
Strong in bulk.
Sealed by corrosion products.
High compressive strength, high tensile strength, high modulus of
elasticity.
Withstands functional stresses thus protecting the residual tooth
structure, cement and crown margins.
It is easily manipulated.
Simple to use and economical.
Coronal radicular stabilization increases the retention of amalgam
cores.
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44. Disadvantages
It needs 24 hours to set before final tooth preparation.
Weak in thin sections.
Mercury content may be of concern to some patients and dentists.
Potential electrolytic action between core and metal crown.
Not intrinsically adhesive.
Corrosion and subsequent discolouration of gingiva or remaining
dentin.
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46. Advantages
Strong compressive strength.
Can be used in a thinner section than amalgam.
Fast setting (either light or chemically cured).
Does not always need a matrix during placement
Avoids mercury controversy.
Ease of manipulation.
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47. Disadvantages
Highly technique sensitive.
Relies on multi-stage dentin bonding requiring effective isolation.
Dentin bond can be ruptured by polymerization contraction.
Minor dimensional changes caused by the co-efficient of thermal
expansion
(3 times higher than tooth) and water absorption –
not usually clinically significant.
difficult to distinguish between tooth and core during preparation.
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48. Glass-Ionomer core
Advantages
Useful for small buildups or to fill
undercuts in prepared teeth.
Fluoride release - anticariogenic
quality but does not guarantee
freedom from secondary tooth
decay.
Intrinsically adhesive.
Similar coefficient of thermal
expansion to tooth.
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49. Disadvantages
Considerably weaker than amalgam and composite.
Low strength and fracture toughness results in brittleness, which
contraindicates the use of G.I.C. build ups in thin, anterior teeth or
to replace unsupported cusps.
Low retention to preformed metal dowels.
Tendency to crack worsened by early instrumentation.
It is soluble, sensitive to moisture.
Adhesive failure can result from contamination of the tooth
surface with cutting debris, saliva, blood or protein.
Not strong enough for a core for an abutment tooth.
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51. CONSERVATION OF TOOTH STRUCTURE
Preparation of canal
Preparation of coronal tissue
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52. Preparation of canal
When creating post space, great care must be used to remove
only minimal tooth structure from canal.
Excessive enlargement can perforate or weaken the root, which
then may split during cementation of post or subsequent
function.
Thickness of remaining dentin is the prime variable in fracture
resistance of the root.
Larger diameter post caused more fractures then smaller posts,
and also induced more stresses.
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53. 1) Adequate apical seal
2) Minimal canal
enlargement
3) Adequate Post Length
4) Positive horizontal stop
5) Vertical wall to prevent
rotation
6) Extension of final
restoration margin on to
sound tooth structure
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54. Preparation of coronal tissue
Endodontically treated teeth have often lost much coronal tooth
structure as a result of caries, previously placed restoration,
preparation of endodontic access cavity or trauma.
If cast post and core is to be used, further reduction is needed to
accommodate a complete crown and to remove undercuts from
the chamber and internal walls. This may leave very little
coronal dentin.
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55. Preservation of coronal tooth structure is necessary to reduce
stress concentration at gingival margins which is also
necessary for creating a ferrule.
Crown lengthening does provide a ferrule but it results in an
unfavorable crown to root ratio thus increasing the leverage on
the root during function.
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57. Preparation geometry
In circular root – parallel post with minimal preparation.
In elliptical root – space between the post and the canal
wall,
- increased preparation weakens the tooth
- retention by threaded post minimizing
the stresses created.
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58. Post length
As post length increases, retention increases, however the
relationship is not linear, an extremely long post may
damage the seal of the root canal fill or risk root perforation
if the apical third is curved or tapered.
Ideally the post should be as long as possible without
jeopardizing the apical seal or the strength or integrity of the
remaining root structure.
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60. Various concepts of post length
Preservation of 3-5mm of gutta percha at apex.
Equal to inciso-cervical or occluso-cervical length of crown.
The post should be longer than the crown.
The post should be 1 ⅓ the length of the crown.
The post should be certain fraction of the length of the root such
as one half, two third, or four fifth.
The post should end halfway between the crestal bone and root
apex.
The post should be as long as possible without disturbing apical
seal.
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61. Post diameter
Increasing the diameter of the post does not provide a
significant increase in the retention of the post, however it
can increase the stiffness of the post at the expense of the
remaining dentin and the fracture resistance of the root.
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62. Post design
A serrated or roughened post is more retentive than a smooth
one, and controlled grooving of the post and root canal
considerably increases the retention of tapered post.
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63. Retentiveness of dowels with regard to dowel configuration
Post configuration
Most retentive
↓
Least retentive
Parallel threaded
Tapering threaded
Parallel serrated
Parallel smoothsided
Tapering smoothsided
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Example
Kurer Crown Saver
Dentatus, Obturation
screw
Parapost
Stainless steel wire
Gold casting
64. Luting agents :
Retention provided by luting cements:
Zinc phosphate cement < Polycarboxylate cement < G.I.C <
Adhesive resin cement
Precaution : Resin cements are affected by eugenol-containing
root canal sealers, which should be removed by irrigation with
ethanol or etching with 37% phosphoric acid if the adhesive is to
be effective.
Removing the smear layer with 17.7% EDTA and 5.25% NaCl
enhanced retention.
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65. Luting method
A. Cement placed
on post
B. Cement Placed
in the canal
C. Cement Placed
both on the post
and in the canal
A
B
C
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67. Stress distribution
Studied by photo elastic materials, strain gauges, finite
element analysis.
The main function of post and core is to improve
resistance to laterally directed forces by distributing them
over as large an area as possible.
Excessive internal preparation of root weakens it, and the
possibility of failure increases.
The greatest stress concentration is found at the shoulder,
particularly interproximally, and at the apex. Dentin
should be conserved in these areas if possible.
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68. - Stresses are reduced as post length increases.
- Parallel-sided posts may distribute stress more evenly than
tapered posts, which may have a wedging effect. However,
parallel posts generate high stresses at the apex.
- Sharp angles should be avoided because they produce high
stresses during loading.
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69. - High stress can be generated during insertion, particularly with
smooth, parallel sided posts that have no vent for cement
escape.
- Threaded post can produce high stress concentration during
insertion and loading, but they have been shown to distribute
stress evenly if posts are backed off a half turn.
- The cement layer results in a more even stress distribution to
the root with less stress concentration.
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70. Rotational resistance
not a problem in areas where sufficient
coronal tooth structure remains, because
rotation is usually prevented by a vertical
coronal wall. In areas where coronal
dentin has been completely lost, a small
groove placed in the canal can serve as
an anti-rotational element.
The groove is normally located where the
root is bulkiest, usually on the lingual
aspect.
Antirotational groove
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71. Slots or Cloverleafs - It is
made at the orifice with a thin,
pointed, tapered diamond stone
or No.557 carbide bur.
Auxiliary pins
Preparing a cavity between the
canal wall and the post and
condensing the amalgam.
Slots or Cloverleafs
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72. Preparation of canal space and tooth :
It is a 3 stage operation :
Removal of endodontic filling material to the appropriate
depth.
Enlargement of the canal.
Preparation of the coronal tooth structure.
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73. Removal of the Endodontic Filling Material
It is recommended that the root canal system should first be
completely obturated and then space made for a post. This will
ensure that the lateral canals are sealed.
With a heated endodontic plugger.
With a rotary instrument
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74. Enlargement of the Canal
- Peeso reamers or a low speed drill.
- The purpose is to remove undercuts
without excessively enlarging the
canal to receive prefabricated posts
- in excessively enlarged or flared
canal, cast posts are preferred.
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75. For Pre-fabricated Posts
- Enlarge the canal one or two sizes with a drill, endodontic filing
or reamer that matches the configuration of the post
- In case of threaded post, the appropriate drill is followed by a
tap
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76. For Custom-made Posts
In noncircular or enlarged canal, preparation to receive the
pre-formed posts will lead to perforations
Often very little preparation will be needed for a custom-made
post.
However, undercuts within the canal should be removed and
some additional shaping is usually necessary.
Careful to avoid perforation in molars
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77. Preparation of Coronal Tooth Structure
After the post space has been prepared, the coronal tooth
structure is reduced for the extracoronal restoration.
Ignore any missing tooth structure and prepare the remaining
tooth as though it was undamaged.
The facial surface (in anteriors) should be adequately reduced
for good esthetics.
Remove all undercuts that will prevent removal of pattern.
Preserve as much tooth structure as possible.
Prepare the finish line at least 2mm gingival to the core. This
establishes the ferrule.
Complete the preparations by eliminating sharp angles and
establishing a smoothwww.indiandentalacademy.com
finish line.
78. Ferrule effect
It originates from combining the Latin for Iron (ferrum) .
Without ferrule
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With ferrule
79. Requirements
•A maximum of 2mm of dentin axial wall height.
•Parallel axial walls.
•Metal must totally encircle the tooth.
•It must be on sound tooth structure.
•It must not invade the attachment apparatus.
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80. Insufficient crown length – What to do?
a. Insufficient crown height
b. No ferrule effect
c. Ferrule effect achieved after
crown lengthing
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81. Surgical crown lengthening
Gingivectomy Procedure
Insufficient Crown Height
Crown Height Increased
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and Crown Given
Gingivectomy Done
83. ORTHODONTIC TOOTH EXTRUSION
Inadequate Crown Height
Eyelet Post Cemented and
Tooth Pulled Out
Sulcular fiberotomy done
every 4 days
3 weeks after rapid eruption.
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Adequate
85. PREFABRICATED POST AND CORE TECHNIQUE
Post Space Preparation
Post adjusted
Post Space Prepared
Luting
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Pre Fabricated Post
Tried-in
cement
placed in canal
89. Using auto polymerising resin
Lubricate canal
Select a loose fitting plastic dowel.
Should extend to full depth of
prepared canal
Notch it
add resin only to canal orifice first or
add resin on post using bead-brush
Technique Or Mix some resin , roll in
cylinder shape and introduced in canal by
Pushing with monomer moistened dowel.
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90. Do not allow resin to harden fully
Loosen and reseat it several times
Once polymerized remove it
Form apical part of post by adding additional resin
reseat and removing Care not to lock it in canal
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91. add additional resin for core
formation
Slightly overbuild the core
and let it polymerize
Shape the core with
carbide finishing burs.
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92. 2.post Using thermoplastic resin material
Plastic rod selected
(Merritt EZ post system)
Should extend to full depth of prepared
canal
Be loose
Should be 1.5-2mm above the occlusal
surface
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93. Lubricate canal
Heat thermoplastic material
Apply on apical aspect of
rod
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94. Insert the rod
Wait for 5-10 secs reseat
Inspect for completeness
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95. Core build up using
autopolymerizing resin
Trimmed to ideal tooth
preparation form
Final preparation.
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96. Indirect procedure
Orthodontic wire bend in
J shape
Verify fit loosely fit, extend
to full depth
If too tight impression will
tear away
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97. Coat wire with adhesive
Lubricate canal (die lubricant)
Fill canal with elastomeric impression
material
(using lentulo spiral)
Seat wire to full length
Syringe some impression
around teeth, insert impression tray
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105. TEMPORIZATION AFTER POST PREPARATION
Post spaced prepared
Cotton wool placed till the apical part of the
preparation over the remaining gutta percha to
prevent temporary cement uniting with the root
filling cement
Pre fabricated post cementedwww.indiandentalacademy.com built up with acrylic and
with temporary Core
temporary crown given
cement
106. Investing and casting
The post-core pattern is sprued on the incisal or occlusal end.
1.0 to 2.0 cc of extra water is added to the investment and a liner
is omitted to increase the casting shrinkage. This results in a
slightly smaller post that does not bind in the canal, and it also
provides space for the cement.
When resin is used, the pattern should remain for 30 minutes
longer in the burnout oven to ensure complete elimination of the
resin
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107. POST REMOVAL
When there is failure of post-endodontic treatment, there
arises a need to remove to post to facilitate non-surgical
retreatment.
In other instances, the endodontic treatment may be
successful but to improve design mechanics, or aesthetics of
a new restoration removal of the existing post may be
necessary.
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108. Methods of removal of posts
Mechanical methods.
Ultrasonic methods.
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115. SUMMARY AND CONCLUSION
Although restoration of endodontically treated teeth has
been rationalized, information from controlled long term
clinical trials is still needed.
As much tooth structure must be preserved as possible
and post and core is basically used to provide retention and
support for a cast restoration.
There is not one post, core or final restoration that can be
used in all – clinical situations. So we have to learn with
these variables and understand the basic concepts of how to
use them to maximum advantage.
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116. BIBLIOGRAPHY
Rosenstiel, Land and Fujimoto. Contemporary Fixed
Prosthodontics. 2nd Ed.; Mosby, St. Louis, 1995.
Shillinburg. Fundamentals of Fixed Prosthodontics. 3rd
Ed.; Quintessence, Chicago, 1997.
Tylman’s Theory and Practice of fixed Prosthodontics. 8th
edition.
Ingle and Bakland. Endodontics. 4th Ed; Williams and
Wilkins, Malvern, 1994.
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117. Cohen and Burns. Pathways to the Pulp. 8th Ed; Mosby, St.
Louis, 2002.
Charles J , Goodame, DDS, MSD and Kenneth J. Splnik,
DDS, The Prosthodontic Management of Endodontically
Treated Teeth: A Literature Review. JProsthod
1994;3:243-250.
Vidyashree V. Nandini, V. Venkatesh Current concepts in
the restoration of endodontically treated teeth, The Journal
of Indian Prosthodontic Society;June 2006;Vol 6;Issue 2
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