Post crown:

It is a full coverage crown that gains its retention

by a post inserted in a prepared root canal. It has a

radicular part inserted in the root canal (post) and

a coronal part outside the root canal (core).

Components of the post crown:

1-The post: It is highly rigid and

should accurately fits the prepared

root canal of the tooth.

2-The core: It is that part rebuilds the

lost part of the coronal tooth

structure

3-The extra coronal restoration:

It is that part restoring both esthetics

and function of the tooth.

Indications of post crown:

1.Individual restoration for badly mutilated endodontically

treated teeth.

2.Retainer for short span bridge (one tooth missed) when the

abutment is endodontically treated

3.When any type of restorations as in the following cases

cannot restore the tooth

- Extensive bilateral proximal caries with pulp exposure.

- Fractured teeth with pulp exposure.

- Endodontically treated teeth with extensive coronal

destruction.

4.Endodontically treated teeth with a sound root.

5.Endodontically treated teeth with long, strong and thick

root.

6.Endodontically treated teeth with perfect apical and lateral

seal.

7.Endodontically treated teeth without periapical pathosis.

8.Endodontically treated teeth with healthy periodontal and

alveolar support.

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.

Contra-Indications of post crown:

1.Improper root canal filling.

2.Presence of periapical pathosis.

3.Weak, thin and curved roots.

4. Heavy, closed or edge-to-edge bite.

5.Patients with diseased periodontal

support.

6.Patients with bad habits as nail

biting and clenching

Advantages of post crown:

1.Provides good retention.

2.Provides strengthening of the mutilated

tooth.

3.Provides the use of root after loss of coronal

portion.

4.High esthetics can be achieved.

5.Malaligned teeth can be easily corrected.

Disadvantages of post crown:

1.Its use is limited to non-vital teeth

2.Root fracture may occur due to improper

canal preparation or improper selection of

the post.

Classification of the post and

core systems.

I. According to the material:

(a) All metallic.

(b) Combination of metal

and non-metal.

(c) All non-metallic.

II. According to retention:

1-Retained by post only.

2-Retained by post and pin or

pins inserted in the dentine of

the coronal portion.

3-Retained by post and collar.

III. According to attachment:

1.Attached post crown:

Where the post, core and

the final crown are

constructed as one piece.

2.Detached post crown:

- Two piece restoration.

- Three-piece restorations.

IV. According to method of construction:

1.Custom-made cast posts: It is cast from extra hard alloys such as :

- Type I\/ Gold alloys.

- Nickel Chromium alloys.

- Cobalt Chromium alloys.

It provides better fit than prefabricated posts.

2.Prefabricated posts (ready-made):

They are supplied in different sizes, shapes and designs.

The majority of these posts are designed to match with special drills for root canal preparation before post insertion.

The coronal aspect of the prefabricated dowel contains a mechanism for retention of the core material e.g. amalgam, composite…etc

The main advantage of using prefabricated posts is the simplicity of the technique.

The prefabricated posts could be classified

in to:

(1) Tapered posts:

Tapered smooth sided posts. Tapered serrated

posts.

Tapered threaded posts.

(2)Parallel-sided posts:

Parallel-sided smooth posts.

Parallel-sided serrated posts.

Parallel-sided threaded posts.

N.BAll the prefabricated posts have a high modulus of elasticity and an

elongation grain structure. Threaded posts are more retentive than

unthreaded posts. The parallel-sided posts are more retentive than

tapered posts. Also serrated posts are more retentive than smooth

posts.

-Root canal preparation.

- Coronal tissue preparation

Conservation

Root canal geometry

Post design

Post length

Post diameter

Retention form

Stress distribution

Rotation resistance

Resistance form

Principles of tooth preparation:

Preparation of endodontically treated

tooth to receive post crown.

Principles of tooth preparation:

I: Conservation of tooth preparation:

(A) Root canal preparation:

- When creating the post space, great care must be taken to remove only minimal tooth structure from the canal.

-The thickness of the remaining dentine.

- In general the internal stresses created during function are less with thinner posts than thicker posts.

- It is recommended that the root canal be enlarged to the amount necessary for the post to fit snugly to the canal.

(B) Coronal tissue preparation

every effort should be made to save as much of the

coronal tooth structure as possible, because this helps

to reduce stress concentrations at the gingival margin

Ferrule design:

a ferrule : is defined as a metal band or ring used to fit the

root or crown of a tooth, as opposed to a crown that

merely encircles core material.

Retention form

A-Preparation geometry.

Root canals should be prepared to give a cavity with parallel-

sided walls or minimal taper (6 degrees).

B- Post length.

Studies have shown that as post length increases, so does the

retention.

D-post surface texture.

A serrated or roughened post is more retentive than smooth one.

C- Post diameter.

Increasing post diameter increases retention.

E-Luting agent.

Post length:

* 2/3 the length of

the root Or

* Equal to the length

of the crown.

* 4-5mm of Gutta

Percha remain to

avoid leakage.

Resistance form

Stress Distribution:

One of the functions of a post and core is to improve resistance to laterally directed forces by distributing them over a large area as much as possible

The influence of post design on stress distribution:

(1) The greatest stress concentrations are found at the shoulder, particularly interproximally and at the apex. Dentine should be conserved in these areas if possible.

(2) Stresses are reduced as post length increases.

(3) Parallel-sided posts reduce stresses better than tapered posts, which have wedging effect. However, parallel-sided posts produce high stresses at the apex.

Sharp angles should be avoided

High stress can be generated during insertion, especially with threaded or unvented parallel sided posts.

The cement layer results in a more even stress distribution to the root with less stress concentrations.

B- Rotational Resistance.

When sufficient coronal

tooth structure remains,

the vertical coronal wall

prevents rotation

Ideal requirements of post and core system:

Post material should have physical properties similar to dentin.

Transfer minimum stresses to the root.

Provide adequate retention to the core.

Should be biologically compatible.

The post must be at least as long as the crown.

The post must have parallel sides or have a max. convergence of

3-5.

Should act as a shock absorber to reduce occlusal stresses.