Post & core final

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Contents
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Introduction
History
Definitions
Why to restore endodontically treated
teeth
• Post & core systems
• Principles of tooth preparation

• Procedure
Post fabrication & Core fabrication
Investing and casting
Evaluation & cementation
• Removal of existing posts
• Conclusion
• References

Introduction


INTRODUCTION:
• The restoration of the endodontically treated tooth is
complicated
• Destruction by caries
• Previous restorations
• Trauma
• Endodontic access preparation
• The endodontically treated teeth require restoration
because of
• dehydrated dentin,
• decreased structural integrity
• impaired neurosensory feedback mechanism

POST

CORE


History
Posts fabricated of gold or silver.
Heat softened adhesive called “mastic
Longevity 15-20 years
1747 Pierre Fauchard

Bone, ivory, animal teeth, natural
tooth crowns
Porcelain


History
“Pivot crown”.
1800’s – Porcelain pivot crown
Dubois de chemant
Early pivot crowns – seasoned wood
Wood posts -“Morbid humors”.
1747 Pierre Fauchard

1878 Richmond crown
1 piece dowel and crown

Post and Core

Definitions
• Dowel (Post):
The dowel is a metal post or other rigid
restorative material placed in the
radicular portion of a non vital tooth.
A dowel usually made of metal is fitted in to a
prepared canal of a natural tooth. When combined
with an artificial crown or core, it provides retention
and resistance for the restoration.
(Glossary of Prosthodontics)

• Core:
Refers to properly shaped and well
substructure,
which
replaces
missing coronal structure and
retains the final restoration.
A centre or a base of a structure. The core is
designed to resemble or become the crown
preparation or crown itself.
(Glossary of Prosthodontics)

• Ferrule (Rosenstile):
Is defined as a metal band that
encircles the external dimension of
the residual tooth.
• Ferrule (Weine) :
A ferrule is a metal ring or cap placed
around the end of a cane or tool, giving it
added strength. The ferrule around the
circumference of the tooth strengthens it by
increasing resistance to wedging forces.

Why to Restore ?
As prosthodontist – abutment for FPD , RPD, Over denture
As a Restorative dentist -Increase the clinical longevity of
these teeth.

Schwartz et al 1983 found that the failure rate of endodontically treated
teeth was almost double in cases with inadequate restoration.
Weine 1996 more endodontically treated teeth are lost due to poor
restoration than to subsequent endodontic failure.

Gutmann 1992
•
•
•
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•

Moisture loss
Architectural changes
Biomechanical behaviour
Dentinal toughness
Collagen alteration

William Robbins 2002
 Dentin diff - vital dentin
 Structure integrity lost
 Neurosensory feedback mechanism impaired

Pre –Operative assessment


Endodontic & Periodontal evaluation:

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Apical seal
Percussion
Palpation
Prescence of sinus tract

 Diagnostic probing
 Mobility


Restorative evaluation

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The amount of remaining tooth structure.
The anatomical position of the tooth.
The functional load on the tooth.
The aesthetic requirements of the tooth.


The amount of remaining tooth structure
Anterior teeth
Do not need posts and full coverage crowns

Sound tooth with access
opening

Lack of Coronal tooth
structure

Anterior teeth are inclined at an angle to the occlusal plane


Posterior teeth
Carry greater occlusal loads

Minimal occlusal access preparations

Teeth with existing restorations involving the marginal ridge or
those with extensive loss of tooth structure
Where ever possible posts should be avoided in posterior teeth
as the roots are often narrow and or curved

Post & Core Systems


Ideal properties of a post
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Maximum protection to root
Adequate retention within root
Maximum retention of the core and the crown.
Maximum protection of the crown
margin cement seal
Pleasing esthetics when indicated
High radiographic visibility
Retreivability
Biocompatibility

• Classification of posts ( D C N A 2002 )

Metallic
Custom cast posts
Prefabricated

Non Metallic
Carbon fiber posts
Zirconia posts
Woven fiber composite post


• Metallic Posts
- PGP [platinum-gold- palladium]
- Nickel –chromium
- Cobalt - chromium
- Stainless steel
- Non oxidizing noble alloys
- Au-pt
- Titanium
Custom cast posts :
Indication
 Multiple cores- in the same arch
 Small teeth
 Angle of cores – to be changed
 All – ceramic crown

combinations

Pre- fabricated posts :

Passive

Active posts

Tapered posts :
 Mimics natural canal shape
Least amount of retention

Parallel posts :
provides greater retention


Indicated :
in short canal space

• Non-Metallic Posts
Carbon fibre posts
Bundles of stretched aligned carbon fibers embedded in
an epoxy matrix
Modulus of elasticity similar to dentine
Can bond to dentine
Unesthetic
Radiolucent
Bond strength of composite core material to
Purton et al 1996
Millstein et al 1999 CFP < Composite core to metal post.

Carbon fibre posts

Trido et al 1999
Bond strength can be increased by air abrasion of CFP.
Drummond et al 1999 :
Found decrease in bond strength after air abrasion.
Stockson et al 1999 :
Retention of CFP = Metal posts.


Tooth coloured posts :

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Zirconium coated CFP
Aesthetic post plus ( Bisco )
All zirconium posts (Cosmoposts & ceraposts )
Fibre reinforced posts
Light post ( Bisco )
Luscent anchor ( Dentatus )
Fibrekor posts

 Zirconium posts modulus of elasticity > Stainless steel
lower fracture resistance than metal posts & inability to bond.
 Difficult to retrive

Resintritt et al in 2000 compared # strength
Titanium post & composite core
&
Zirconium post & composite core
↨ Vectris resin post & composite Core
↨ Custom cast gold post & core
↓ IPS Empress & All Zirconium


CORE
Steven M. Morgano & Susan E. Brackett 1999
Desirable features of a core material :
Adequate compressive strength
Sufficient flexural strength
Biocompatibility
Resistance to leakage of oral fluids at the core/tooth interface.
Ease of manipulation.
Ability to bond to remaining tooth structure
Thermal co-efficient of expansion and contraction
Dimensional stability
Minimal potential for water absorption &
Inhibition of dental caries.

Classification of core materials :

Cast core

Plastic core materials

Metal

Amalgam

Ceramic to Zirconia
dowels

Glass ionomer cement
Resin modified GIC
Dual cure fibre reinforced cores


Cast core
Kantor and pines 1977 teeth little coronal structure the cast gold
post and core was superior to a stock post and composite resin core.
Ceramic to Zirconia dowels
Pissis 1995 proposed a “Monobloc” technique for fabrication of a
post and core and a crown as a single component made out of glass
ceramic material IPS empress.


Amalgam
Nayyar, Walton, Leonard 1980 reported a technique of
amalgam core build up

Hoag ED, Dwyer TG 1982 Amalgam can be used for core build
ups Due to its self – sealing proprieties, durability and good
working characteristics

Barban 1970 was one of the first to suggest the use of
composite resin to fabricate cores.
Linde LA 1983 found that composite cores showed significantly
greater marginal leakage compared with amalgam cores.

MC lean 1985 GIC can be tooth substance remains and where
limited loading is anticipated.
Resin modified GIC not recommended in high stress situations.

Principles of tooth preparation


• Conservation of tooth structure
Preparation of the canal
Preparation of coronal tissue
• Retention form
Anterior teeth
Posterior teeth
• Resistance form
Stress distribution
Rotational resistance

Conservation of tooth
structure
Preparation of the canal :
• Remove minimal tooth structure form the canal.
• Excessive enlargement can perforate or weaken the root
~ Thickness of remaining dentin – Fracture resistance from
Helfer AR et al 1972. teeth cemented with thicker posts (1.8 mm)
fractured more easily than those with a thinner (1.3 mm) one.

Photo elastic studies also have show that internal stresses are
reduced with thinnerwww.indiandentalacademy.com
posts.

Most roots have proximal concavities
Felton DA 1991 said that most root fractures originate from these
concavities because the remaining dentin thickness is minimal.

Root canal should be enlarged only enough to enable the post
to fit accurately yet passively while insuring strength and
retention.

Preparation of coronal tissue :

Milton P and Stein R S 1992 if more than 2 mm of coronal
tooth structure remains, the post design probably has a limited
role in the fracture resistance of restored tooth.

A key element of tooth preparation when using a dowel and core is
the incorporation of a www.indiandentalacademy.com
ferrule.

CERVICAL FERRULE
A ferrule is a metal band or ring used to fit the root or crown of a tooth.

• Increased fracture resistance
• Antirotational

With Ferrule

Without Ferrule

The effectiveness of the ferrule has been evaluated by a variety
of methods, including
Fracture testing
Impact testing
Fatigue testing and
Photo elastic analysis.
1.5 mm of ferrule height
Philip et al 2005 have investigated the resistance to static loading of
endodontically treated teeth with uniform and non uniform ferrule
configuration
2 mm uniform

> 0.5 – 2mm ferrule height non uniform

2 mm uniform &
0.5 – 2mm ferrule height non uniform


>

NO ferrule

what if tooth has inadequate coronal tooth structure to
create a ferrule ?
•Consider crown lengthening and or extrusion
Surgical :Crown lengthening
Allows ferrule
Less favourable crown root ratio
increased leverage on the root during function
Gegauff 1999: showed that creating ferrule through crown
lengthening resulted in a weaker rather than a stronger restored tooth.
Orthodontic extrusion


Retention
form

Post retention is affected by the
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Preparation geometry
Post length & diameter
Surface texture and
Luting agent.


Anterior teeth

Preparation geometry :

Canals

Elliptical cross section
Must be prepared with restricted amount of taper 6-8
Taper increases – retention decreases similar to extra coronal
preparation.

Circular cross section
Prepared with a twist drill or reamer to provide a cavity with
parallel walls or minimal taper.

Threaded posts :
Increase the retention
Not recommended because of residual stress in dentin.

Standlee JP et al 1978 confirmed that parallel sided posts more
retentive than tapered posts and that threaded posts are most
retentive.


Post length :
Studies have shown that an post length increases, so does
retention. However the relationship is not linear.
A post that is too short will fail

Post that is too long
Ideally, as long as possible

5 mm apical seal
not les than 3 mm


Post diameter :
Increasing the post diameter in an attempt to increase retention
Ideally
 No wider 1/3 root
2 mm of tooth structure.
Tilk M A et al 1979 :1500 teeth (125 of each tooth)
0.6 mm – Mandibular incisors
1.0mm – Maxillary CI, Max and Man canines,
Palatal root of max I molar
0.8 mm Other teeth.

Shillingburg et al 1982 in a study of 100 teeth
0.7 mm – Mandibular CI
1.7 mm – Maxillary CI.


4) Post surface texture :

A serrated or roughened post is more retentive than a smooth one.
 Controlled grooving of the post and root canal increases the
retention of a tapered post.

5) Luting agent :
Traditional cements – little effect
Adhesive resin luting cements – increased retention
Note: irrigation with ethanol or etching with 37% phosphoric acid

Posterior teeth :
Long posts avoided – curved roots and elliptical or ribbon shaped
canals.
Retention is better provided by two or more relatively short posts
in the divergent canals.

Cast core can be used (made in sections that have different paths
of with drawl).


Resistance
form
Stress distribution
The influence of post design on stress distribution has been
tested using.
Photo elastic materials.
Strain gauges and
Finite elements analysis
The greatest stress concentrations are found at the shoulder,
particularly interproximally, and at the apex.


Stresses are reduced as post length increases.

Parallel sided posts

Tapered posts

High stress can be generated during insertion, parallel sided posts
Sharp angles should be avoided because they produces high
stresses during loading

Threaded posts

Backed off a half turn
Cement layer

Rotational resistance :
Rotation can be prevented by vertical coronal wall.
a small groove placed in the canal
root is bulkiest – lingual aspect

Procedure


3 stage operation.
1. Removal of the root canal filling material to the appropriate depth.
2. Enlargement of the canal
3. Preparation of the coronal tooth structures


Root canal treatment


Post & core treatment


1.REMOVAL OF THE ENDODONTIC FILLING
MATERIAL
1. Chemical Removal
2. Thermal Removal
3. Mechanical Removal

Schnell FJ 1978 and Bourgeois R S and Lemon RR (1981)
gutta-percha can be removed with a warm condenser immediately
after obturation.
Dickey DJ et al 1982 Rotary instrument can disturb
apical seal if used immediately after obturation.

Steps in removal of gutta-percha & Enlargement of the canal

Calculate the appropriate length of the post
IF gutta-percha is old and has lost its thermoplasticity, use a
rotary instrument (Peeso-Reames or Gates Glidden drills)
Before enlargement of the canal, the type of post system to
be used for fabrication of the post and core must be chosen.

2.PREPARATION OF THE CORONAL
TOOTH STRUCTURE :
Remove all internal and external undercuts

prepared perpendicular to the post, to create a positive stop & to
prevent over seating and splitting of the tooth.
If insufficient tooth structure remains for this feature, an
antirotation groove should be placed in the canal
Complete the preparation by eliminating sharp angles
and establishing smooth finish lines.

3.POST & CORE FABRICATION :
Prefabricated post :

Custom-made posts :
Direct procedure : patients mouth

Indirect procedure : laboratory


Direct method using Pre-fabricated post

Post selected

Core build up

Finishing

Basic Procedure for
Custom Post & Core
Fabrication


Direct method

1
2
3
4
5
6
7
8

9

Direct pattern for multi-rooted teeth :


Indirect procedure :
Pieces of orthodontic wire
Lubricate the canals
a lentulo spiral
syringe in impression material

Apply a thin coat sticky wax to the plastic post
after lubricating the stone cast,
add soft inlay wax in increments
Investing and casting

INVESTING AND CASTING
Cast post-and-core should fit somewhat loosely in the canal
Casting should be slightly undersized
Omitting the usual ring liner or
Casting at lower mold temperature
Extra-hard partial denture gold (ADA type IV) or
nickel chromium alloys
EVALUATION :
Casting defects should not interfere with
seating of the post; otherwise, root fracture
will result.

CEMENTATION :
Post-and-cores should be inserted with gentle pressure
A rotary (lentulo) paste filler or cement tube

a parallel-sided post is being used, a groove should
be placed along the side of the post

Over denture abutment


Removal of existing posts :
Thin-beaked forceps
Ultrasonic removal
Post puller
Masserann kit
Special hollow end-cutting tubes (or trephines)
Drilled out
If the fractured post is of the threaded type a groove cut in the end
of it may enable it to be unscrewed

Fractured post

Before

Ultrasonically
powered chisel

Masseran trepan and
ultrasonic chisel.

Masseran trepan

After

Conclusion


R
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F
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N
C
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S

7. Harold Gerstein, "Technique In Clinical Endodontics" 34787.
8. Pitt Ford, "Problem-solving in Clinical Practice" 149-164.
9. Gutmann, "Problem-solving in Endodontics" 3rd Edn, 32546.
10.Stephen Cohen, "Pathways of the Pulp", 8th Edn, 765-795.
11. Franklin S. Weine, "Endodontic Therapy" 4th Edn, 653698.
12. Tylman's "Theory and Practice's of Fixed Prosthodontics",
8th Edn, 407-417.
13. Herbert T. Shillingburg, "Restoration of the Endodontically
Treated Tooth" 1982Edn. .
14. Herbert Shillingburg, "Fundamental of Fixed
Prosthodontics" 3rd Edn, 194-209.
15. Herbert Shillingburg, "Fundamental of Tooth Preparation"
2nd Edn, 321-358.
16. Rosensteil, "Contemporary Fixed Prosthodontics" 3rd
Edn., 272-312.
17. Endod Dent Traumatel1998; 14: 59-63.

Post & core final

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