3. post retained crown-midterm3

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.