Post Selection and Post Space

Preparation
A seminar submitted to Endodontics Department
( Endodontics I )

Prepared by
Tasneem Mostafa Saad Khalil
Resident of Fixed Prosthodontics - Assiut University
Under supervision of
Dr. Abanoub Raouf
Lecturer of Endodontics - Alminya University
Introduction
- Restorations of endodontically treated teeth are designed to :

-Protect remaining tooth from fracture.

-Prevent root canal system reinfection.
-Replace missing tooth structure.
Post and core system
A restoration consists of

- post that fills prepared root canal.

- core inserted into pulp chamber after proper

coronal tooth preparation.
 CLASSIFICATION OF POST CROWN SYSTEM
I- According to the material
A- All metallic B- All non-metallic C- Combination

• metal alloy. • ZrO ceramic posts or Carbon

1-Metal post crown with non-
fiber posts & non-metallic
1-Prefabricated core & all-ceramic crown. metallic veneering material.
2- Casted • Carbon fiber post:
• Carbon-epoxy material.
• Carbon fibres embedded in 2-Metal post & composite or glass
• Disadvantages:
epoxy resin matrix. ionomer core.
1- Altered esthetics by grey color Properties:
especially in anterior teeth. 1.High fatigue, tensile strength.
2- Stress concentration within radicular
2-Surface roughness by 3-Metal post & core with veneered
mechanical adhesion to resin.
dentin → root fracture. crown.
• Ceramic post:
• ZrO posts (ceramic posts) is
parallel-sided with slightly
tapered toward the apex.
 CLASSIFICATION OF POST CROWN SYSTEM
II- According to retention

A. Post only B- Post & Pins C- Post & Collar

• Collar → a type of preparation
• Retained by post only •
A post inserted in the prepared indicated to ↑ retention &
prevent restoration rotation.
• Collar is indicated when there is
inserted in the prepared root root canal & pins drilled in the enough remaining coronal
portion.
canal. dentine of the root face. • Remaining coronal portion (the
root face) is bevelled buccally &
lingually .
 III- According to attachment

A. Attached post crown (One piece post

B- Detached post crown
crown)

•
a-Two pieces detached post crown:
• Post crown is constructed cemented as one unit . • Post & core are constructed as one cast piece &
• Cast post & core with or without esthetic facing of its cemented first. Then, extra coronal restoration is
constructed as second cast piece & cemented
top part . It is the worst type because : separately .
• b-Three pieces detached post crown:
• 1-More liable to construction defects. • Prefabricated post (ready made post) is cemented first
• 2-Difficult to remove crown in case of facing fracture . (first piece).
• Build up the coronal portion (a core), either of amalgam ,
composite or reinforced glass ionomer(second piece).
• Extra-coronal restoration is then constructed &
cemented(third piece) .
Classification of prefabricated posts:

1-According to materials:

a-Metal posts:
St.St, Ti, Pa, Au-Pl, CoCr, NiCr.
b-Non-metal posts:
Glass fibre, Carbon fibre, Ceramic posts.

2-According to retention:

a-Passive posts:
Non-threaded posts → Cemented inside the prepared root canal.
b-Active posts:
Threaded posts → Mechanically engage D wall of the prepared root canal.
Give more retention than the cemented type but may induce stresses & cracks in root.
c-Hybrid post:
Active post in the cervical part of the root canal & passive in the apical part .
Classification of prefabricated posts :

3-According to design:

a-Tapered sided posts:

Produce wedging stresses inside the root canal .
b-Parallel sided posts:
Distribute forces better & are more retentive .
Flex-post with split shank that closes during insertion → reduces stresses exerted inside root
canal & minimizes liability of root fracture.
c-Parallel-Tapered sided posts:
Parallel sided posts throughout its length except its most apical part are tapered
Post Space Preparation
 Post Space Preparation

1- Root canal preparation:

Minimal removal of sound tooth structure from the canal wall.

Over-enlargement may lead to → perforation or weakens the root →

may fracture during cementation of the post or during function

For optimum stress distribution & retention → Canal prepared so that dowel

length should be equal to the crown length or 2/3 the length of the root

Longer posts → More retention.

Shorter posts → Root fracture.

Canal prepared so that at least 4-5mm of gutta percha should remain

undisturbed at the apex to avoid leakage.

2- Coronal portion preparation:

 Preservation of sound tooth structure → to provide retention & support to the core
material.

 Only caries & undermined tooth structure & parts that interfere with the path of insertion
should be removed.

 Coronal portion preparation should be done so that the crown margin should extend 1.5 to
2 mm. apical to the core to provide a ferrule.

• Functions of a ferrule:

• 1- Binds tooth structure together → ↑ resistance to lateral & occlusal forces.

• 2- ↓ stress concentration at the post/core junction .

• 3- Maintains integrity of the cement seal & enhances resistance to dislodgement.

B- Retention form:
 Resistance of restoration to displacement along the path of insertion.
 Retention of post crown system is affected by:
1- Preparation geometry (Root canal shape):
 Parallel-sided root canal → More retentive than tapered canal .
 Parallel posts → More retentive than tapered posts.
2- Post design:
 Threaded posts → More retentive than unthreaded Posts.
 Threaded posts → Highest retention followed by serrated posts.
 Serrated posts → More retentive than smooth sided posts due to its
mechanical interlocking with cement.
3- Post length:

 Long post → More surface area for contact friction with tooth structure → More

retention

 Ideally, post length should be 2/3 of the root length leaving 4-5 mm of the root canal

filling material for good apical seal.

 Post length should be equal or longer than the length of the core & the extra-coronal

restoration, as the resistance arm should be equal or longer than the force arm.
4-Post diameter:

 The thicker the post → ↑ S.A → More retention.

 Canal widening → May cause weakening of the root.

 Post diameter → Should not exceed 1/3 of the total root diameter .
5- Luting agents :

 Adhesive cements → more retentive than the conventional cements

such as phosphate & glass ionomer cement.

 Newly introduced adhesive resin cements such as composite resin

cement, Zn polycarboxylate cement, show improvement in post
retention.
Recent advances in post systems
 Recent advances in post systems
• PEEK Posts
A high-performance polymer, polyetheretherketone (PEEK) has recently
been introduced in dentistry.
It has been used for the fabrication of implant fixtures, fixed and
removable dental prosthesis frameworks and for implant frameworks
and restorative implant parts.
Modified PEEK material containing 20% ceramic fillers (BioHPP; Bredent
GmbH) has good mechanical properties and excellent biocompatibility.
It can be used for the fabrication of prostheses either by injection
molding or CAD-CAM procedures.
Advantages of PEEK material :

• 4- GPa modulus of elasticity, making it as elastic as bone and allowing it

to act as a stress breaker, reduce forces transferred to restoration and
root.
• Elimination of allergic reactions
• Good wear resistance
• Good polishing properties
• Low plaque affinity
Disadvantages :

• Microleakage
• Behaviour under fatigue loading is not clear
• Occlusal adjustments must be done
• Can’t be polished easily, intraorally after definitive cementation which
results in a dull occlusal surface.
Endocrown
Endocrown is alternative to post-core system .
In the past, the endocrown described as adhesive endodontic crowns
and characterized as total porcelain crown fixed to endodontically
treated posterior teeth .
In recent study, endocrown is fabricated from hybrid resin composite or
ceramic , is a monolithic bonded restoration and using the entire
extension of the pulp chamber and possibly the root canal entrances as
a retentive resource instead of the intra radicular post.
Advantages of endocrown

• Conservative with proper marginal stability that enhanced by retaining

maximum enamel to improve adhesion.
• Good seal of the root canal opening, and prevent micro leakage which
in turn affecting the long-term prognosis of ETT.
Disadvantages :
• High risk of fracture failure because of the absence of a metal or high-
strength ceramic substructure as in conventional full-crown.
BONDABLE REINFORCEMENT FIBER POST
( RIBBON FIBRE POST )
• Bondable reinforcement fiber, a fourth-generation bonding agent and
a dualcure hybrid composite as the core build-up.
• Consists of polyethylene woven fibers that are treated with a cold-gas
plasma.
• Embedded in conventional resin composite has been advocated for
coronoradicular stabilization of pulp-less teeth.
• For this technique to work well, there should be sufficient light to
reach the depth of the post space.
Advantages :
• Ribbond maintains the natural strength of the tooth and eliminates
the possibility of root perforation.
• It conforms to the natural contours and undercuts of the canal and
provides additional mechanical retention.
• There are no stress concentrations at the tooth-post interface.
• The Ribbond post and core is passive and highly retentive.
Cosmopost
• It is a ceramic post system and is indicated mostly in aesthetically
important anterior region of maxilla and mandible.
• Cylindrically shaped with a conical tip, the Cosmopost is available in
two relatively wide diameters (1.4 mm and 1.7 mm).
• The 1.4mm post is generally indicated in the anterior region: only for
the lateral incisors and in the mandible for the central and lateral
incisors, maxillary and mandibular premolars.
• The 1.7mm Cosmopost is used for the four canines and the central
incisors in the maxilla (distal canal in the mandible, palatal canal in
maxilla).