• Introduction• History• Definitions • Why to restore endodontically treated

teeth• Post & core systems• Principles of tooth preparation

Contents

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

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

INTRODUCTION:

POST

CORE

History

1747 Pierre Fauchard

Posts fabricated of gold or silver.

Heat softened adhesive called “mastic

Longevity 15-20 years

Bone, ivory, animal teeth, natural tooth crowns

Porcelain

History“Pivot crown”.

Early pivot crowns – seasoned wood Wood posts -“Morbid humors”.

1747 Pierre Fauchard

1800’s – Porcelain pivot crown Dubois de chemant

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.

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.

Why to Restore ?

Gutmann 1992 • 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:

Apical seal Percussion Palpation Prescence of sinus tract

Diagnostic probing Mobility

Restorative evaluation

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 structureAnterior teeth

Do not need posts and full coverage crowns

Anterior teeth are inclined at an angle to the occlusal plane

Sound tooth with access opening

Lack of Coronal tooth structure

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

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 Non Metallic

Custom cast posts

Prefabricated

Carbon fiber posts

Zirconia posts

Woven fiber composite post

Multiple cores- in the same arch Small teeth Angle of cores – to be changed All – ceramic crown

- PGP [platinum-gold- palladium]- Nickel –chromium- Cobalt - chromium- Stainless steel - Non oxidizing noble alloys - Au-pt - Titanium

Custom cast posts :

• Metallic Posts

Indication

combinations

Pre- fabricated posts :

Tapered posts :

Mimics natural canal shape Least amount of retention

Parallel posts :

provides greater retention

Active posts

Indicated : in short canal space

Passive

Carbon fibre posts

Bundles of stretched aligned carbon fibers embedded in an epoxy matrix

Modulus of elasticity similar to dentine

UnestheticRadiolucent

Can bond to dentine

Purton et al 1996Millstein et al 1999

Bond strength of composite core material to CFP < Composite core to metal post.

• Non-Metallic Posts

Trido et al 1999 Bond strength can be increased by air abrasion of CFP.

Drummond et al 1999 :

Stockson et al 1999 : Retention of CFP = Metal posts.

Found decrease in bond strength after air abrasion.

Carbon fibre posts

Tooth coloured posts :

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 contractionDimensional stability Minimal potential for water absorption & Inhibition of dental caries.

Classification of core materials :

Cast core Plastic core materials

Metal

Ceramic to Zirconia dowels

Amalgam

Glass ionomer cement

Resin modified GIC

Dual cure fibre reinforced cores

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.

Kantor and pines 1977 teeth little coronal structure the cast gold post and core was superior to a stock post and composite resin core.

Cast core

Ceramic to Zirconia dowels

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

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

Amalgam

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

• Remove minimal tooth structure form the canal. • Excessive enlargement can perforate or weaken the root~ Thickness of remaining dentin – Fracture resistance from

Preparation of the canal :

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 thinner posts.

Conservation of tooth structure

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

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

Most roots have proximal concavities

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 ferrule.

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

CERVICAL FERRULE

• Increased fracture resistance• Antirotational

With Ferrule Without Ferrule

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 ?

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

•Consider crown lengthening and or extrusion

Anterior teeth

Preparation geometry Post length & diameter Surface texture and Luting agent.

Retention form

Post retention is affected by the

Preparation geometry :

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

Canals

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

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

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

Threaded posts :

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

Ideally, as long as possible 5 mm apical seal not les than 3 mm

Post length :

Post that is too long

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 molar0.8 mm Other teeth.

Shillingburg et al 1982 in a study of 100 teeth

0.7 mm – Mandibular CI1.7 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

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).

Posterior teeth :

Stress distribution

Photo elastic materials. Strain gauges and Finite elements analysis

The greatest stress concentrations are found at the shoulder, particularly interproximally, and at the apex.

Resistance form

The influence of post design on stress distribution has been tested using.

Stresses are reduced as post length increases.

Sharp angles should be avoided because they produces high stresses during loading

High stress can be generated during insertion, parallel sided posts

Parallel sided posts Tapered posts

Threaded posts

Rotational resistance :

Rotation can be prevented by vertical coronal wall.

a small groove placed in the canal

root is bulkiest – lingual aspect

Backed off a half turn

Cement layer

Procedure

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

3 stage operation.

Root canal treatment

Post & core treatment

1.REMOVAL OF THE ENDODONTIC FILLING MATERIAL 1. Chemical Removal

2. Thermal Removal3. 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

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.

Calculate the appropriate length of the post

2.PREPARATION OF THE CORONAL TOOTH STRUCTURE :

Remove all internal and external undercuts

Complete the preparation by eliminating sharp angles and establishing smooth finish lines.

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

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

12

3

4

5

6

7

89

Direct method

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

Casting should be slightly undersized Cast post-and-core should fit somewhat loosely in the canal

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.

Post-and-cores should be inserted with gentle pressure CEMENTATION :

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

Special hollow end-cutting tubes (or trephines) Drilled out

Masserann kit

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 Ultrasonically powered chisel

Masseran trepan and ultrasonic chisel.

Masseran trepan

Before After

Conclusion

REFERENCES

1. E. Nicholis, "Endodontics", 3rd Edn, 1984,353-76.2. Pitt Ford, "Harty's Endodontics in Clinical Practice", 4th

Edn, 251-281.3. Grossman, "Endodontic Practice" 316-317.4. Ingle, Chap-19, "Restoration of Endodontically Treated

Teeth", 2002 Edn., 913-950.5. Mumford & Jedvnakiewicz, "Principles of Endodontics",

1988, 163-83.6. Walton Torabinejad, "Principles and Practice of

Endodontics", 3rd Edn, 268-81.7. Harold Gerstein, "Technique In Clinical Endodontics" 347-

87.8. Pitt Ford, "Problem-solving in Clinical Practice" 149-164.9. Gutmann, "Problem-solving in Endodontics" 3rd Edn, 325-

46.10.Stephen Cohen, "Pathways of the Pulp", 8th Edn, 765-795.11. Franklin S. Weine, "Endodontic Therapy" 4th Edn, 653-

698. 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: 59-63.18. J Prosth Dent 1992; 67: 458-67.19. Int Endo J 2002; 35: 575-581.20. J Prosth Dent 1990; 63: 529-3621. J Prosth Dent 1977; 38: 515-2522. J Prosth Dent 1970; 23: 58-6523. J Prosth Dent 1993; 69: 32-6.24. J Prosth Dent 1985; 53: 631.25 J Prosth Dent 1984; 52: 28.26. J Prosth Dent 1970; 23: 173. 27. J Prosth Dent 1972; 28: 405.28. J Endod 1982; 8: 154.29. J Prosth Dent 1984; 51: 785, 30. J Prosth Dent 1978; 39: 401. 31. J Prosth Dent 1982; 47: 177. 32. Quint lnt 1999; 30: 383 -39233 B D J 2005;198:395-40434 B D J 2005;198:463-47135. B D J 2005;198:533-541