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POST-RETAINED CROWNPOST-RETAINED CROWN
(Restoration of the Endodontically Treated Tooth)
Cemented Dowel Crown
Cemented dowel crown(radiographic view)
Treatment Planning
Endodontically treated tooth need to be assessed carefully for the following:
1. Good apical seal
2. No sensitivity to pressure
3. No exudates
4. No fistula
5. No apical sensitivity
6. No active inflammation
Disadvantages to the routine use of a cemented post:
a. Placing the post require an additional operative procedure
b.Preparing a tooth to accommodate the post removes additional tooth structure
The use of a parallel-sided post in a tapered canal requires considerable enlargement of the post space, which can weaken the root significantly.
c. It may be difficult to restore the tooth later, when a complete crown is needed, because the cemented post may have failed to provide adequate retention for the core material.
d. The post can complicate or prevent future endodontic retreatment if this becomes necessary.
Requirements for traditional core and dowel construction:a. Ideally the length of post
should be equal to, at least, the length of the estimated clinical crown.
b. The post must have an occlusal stop to prevent displacement apically. This is of vital importance since displacement toward the apex commonly results in fracture of the prepared root.
c. Included in this construction should be resistance to rotational forces.
d. Posts should be of sufficient thickness to resist displacement and assist stabilization.
Clinical crown
Apical seal
PREPARED TOOTH for
DOWEL CROWN
ferrule
Principle of Post Support (Retention)A. Minimum post length should equal restored
crown length or engage 2/3 of natural root
B. Cylindrical posts are more retentive than similarly size tapered posts
C. Wrought (bent/twisted/formed) gold alloy posts are two to four times stronger than cast gold alloy posts of equal diameter
D. Serrated posts are 30% to 40% more retentive than are smooth posts
3 Stages in Tooth Preparation
1. Removal of the root canal filling material to the appropriate
depth
2. Enlargement of the canal
3. Preparation of the coronal tooth structure
REMOVAL OF THE ENDO FILLING MATERIAL
2 Methods of Removing Gutta Percha:
a. With a warmed condenser
b. With a rotary instrument (sometimes used with a chemical agent such as chloroform)
Endo condenser / plugger
Gutta condenser
Steps: (using a warmed condenser)
1.Before removing gutta percha, calculate the appropriate length of the post.
2. Avoid the apical 5mm if possible.
5mm. Apical seal
3. To prevent aspiration of an endo. instrument, apply a rubber dam before preparing the post space.
4. Select an endo. condenser large enough to hold heat well but not so large that it binds against the canal walls.
5. Mark it at the appropriate length, heat it, and place it in the canal to soften the gutta percha.
6. When the gutta percha has been removed to the appropriate depth, shape the canal as needed.
ENLARGEMENT OF THE CANALFor Prefabricated Posts
1. Enlarge the canal one to two sizes with a drill, endo file and reamer that matches
the configuration of the post
2. Use a prefabricated post that matches standard endo instruments
3. Be especially careful not to remove
more dentin at the apical extent of the post space than is necessary
For Custom-made Posts1. Use custom-made posts in canals
that have a non-circular cross section or extreme taper. Enlarging canals to conform to a preformed post may lead to perforation.
2. Be most careful on molars to avoid
root perforation.
PREPARATION OF THE CORONAL TOOTH STRUCTURE
1. Ignore any missing tooth structure and prepare the remaining tooth as though it were undamaged.
2. Be sure that the facial surface of the tooth is adequately reduced for good esthetics.
3. Remove all undercuts that would prevent withdrawal of the pattern
4. Remove any unsupported tooth structure, but be careful to preserve as much of the crown as possible.
5. Be sure that part of the crown is prepared perpendicular to the post.
6. Complete the preparation by eliminating sharp angles and establishing a smooth finish line.
Post Fabrication:
a. Prefabricated Posts -One advantage of using prefabricated posts is the simplicity of the technique -A post is selected to match the dimensions of the canal, and only minimum adjustment is needed for seating it to the full depth of the post space -Coronal half of the post may have an inadequate fit because the root canal has been flared, this is corrected by adding material when the core is made
PREFABRICATED POSTS
b. Custom-made Posts
-Can be cast from direct pattern or an indirect one
-Direct technique utilizes autopolymerizing resin and is indicated for single canals whereas an indirect technique is more appropriate for multiple canals
Core Fabrication: The core replaces missing coronal tooth structure, and thereby forms the shape of the tooth preparation.
It can be shaped in resin or wax and added to the post pattern before the assembly is cast into metal.
The core can also be cast onto most prefabricated post systems.
A third alternative is to make the core from a restorative material such as amalgam, GI or composite resin.
AA
1 2
34
Casted metal post and core
Post & core pattern
Core pattern using wax
Casted post & core cemented into the tooth
Wax pattern for multiple root tooth
Wax pattern for a single root tooth
A
B
C
AVAILABLE POST AND CORE SYSTEMS
ADVANTAGES DISADVANTAGES
Amalgam Conservative of tooth Low tensile strength structure Corrosion with base Straightforward technique metal
GI same Difficult condensation
Low strength
Composite same Low strength Resin Continued polymerization
Microleakage
Custom cast High strength Less stiff than Post & Core Better fit than prefabricated wrought
Time-consuming Complex procedure
ADVANTAGES DISADVANTAGES
Wire post & High strength Corrosion of base metal Cast core High stiffness Pt-Au-Pd wire expensive
Tapered pre- Conservative of tooth Less retentive than ||
sided fabricated structure or threaded system post High strength & stiffness
|| sided pre- High strength Precious-metal post
fabricated post Good retention expensive Comprehensive system Corrosion of SS
Less conservative of tooth
structure
Threaded post High retention Stresses generated in the
canal may lead to fracture
Not conservative of coronal and radicular tooth
structure
RECOMMENDED USE PRECAUTION
Amalgam Molars with adequate coronal tooth Not recommended in structure teeth under
lateral load (anteriors)
GI Teeth with minimum tooth Not recommended in structure missing teeth under lateral load
Composite same same
Custom cast Elliptical or flared canal Care to remove Post & Core
nodules before try in
RECOMMENDED USE PRECAUTION
Wire post & Small circular canal Care to avoid
Cast core perforation during prep.
Tapered pre- same Not recommended for fabricated post excessively
flared canals
|| sided pre- same Care during prep.
fabricated post
Threaded post Only when maximum Care to avoid retention is essential fracture during
seating
Tapered threaded post(jacket crown)
Tapered smooth-sided post
Tapered threaded post(fixed bridge)
SomeTechniques
In the Removal of Fractured
Post
Post Removal by High Speed Bur A post that has fractured within A post that has fractured within
the root canal cannot be removed the root canal cannot be removed with a post puller or forceps. The with a post puller or forceps. The post can be drilled out, but great post can be drilled out, but great care is needed to avoid deviation.care is needed to avoid deviation.
This technique is best limited to This technique is best limited to relatively short fractured posts.relatively short fractured posts.
Post removal by high speed bur
A B
Masseran Technique
Uses special hollow end-cutting tubes or trephines to prepare a thin trench around the post.
Removal or retrieval can be facilitated by using an adhesive to attach a hollow tube extractor or by using a threaded extractor.
Maxillary incisor with a fractured post inside the canal (A and B).
A B
C. The diameter of the post is gauged with a sizing tool.
D. The selected trephine is carefully rotated counter-clockwise to create a narrow channel around the post.
C D
E. When the instrument has removed sufficient material, the post is recovered.
F. The fractured crown and post after removal.
FE Fractured post
Cementation of Post and Core
A rotary (lentulo) paste filler or cement tube is used to fill the canal with cement.
The post is first coated with cement.
It is important that the luting agent fill all dead spaces within the root canal system.
The post and core is inserted gently The post and core is inserted gently to reduce hydrostatic pressure, to reduce hydrostatic pressure, which could cause root fracture.which could cause root fracture.
It is recommended that a It is recommended that a groove be placed along the groove be placed along the side of the post to allow side of the post to allow excess cement to escape, if excess cement to escape, if a parallel-sided post is a parallel-sided post is being used.being used.