ATYPICAL TOOTH PREPARATION

SEMINAR BY

Dr.VINAMRA DHARIWAL

CONTENTS

Part 1 – Basics of tooth preparation

a. Definition

b. Caries control

c. Preparation objectives

d. Finish lines

e. Principles of tooth preparation

f. instrumentation

Part 2 –

a. Preparation modification for damaged teeth

b. Atypical tooth preparation

c. preparation modification for special situation

d. preparation for periodontally weak teeth

TOOTH PREPARATION

Tooth Preparation is defined as the

mechanical treatment of dental

disease or injury to hard tissues

that restores a tooth to original

form.

CARIES CONTROL

Why important

Removal procedure

Sequence of removal

PREPARATION OBJECTIVES

1. Reduction of the tooth in miniature to provide retainer

support.

2. Preservation of healthy tooth structure to secure

resistance form

3. Provision for acceptable finish lines

4. Performing pragmatic axial tooth reduction to

encourage favorable tissue responses from artificial

crown contours, i.e., fluting of molars.

1. Sequence of tooth preparation

2. Contour

3. Intracoronal Vs Extra coronal

4. Tooth structure conservation

5. Gingival termination of

preparation

CLINICAL CONSIDERATION

Errors in tooth preparation

Selection of retainer

Occlusion and tooth preparation

Difficult restorative treatment

OTHER CONSIDERATION

FINISH LINES

1. Supragingival Vs Subgingival Margins

2. Types of finish lines

PRINCIPLES OF TOOTH PREPARATION

1. Preservation of tooth structure

2. Retention and resistance form

3. Structural durability of the

restoration

4. Marginal integrity

5. Preservation of the

periodontium

RETENTION

Taper and retention

Surface area

Area under shear

Surface roughness

RESISTANCE

Method to analyze resistance form

Factors influencing resistance

1. Leverage

2. Length

3. Width

4. Taper

5. Rotation around vertical axis

6. Path of insertion

INSTRUMENTATION

1. Water colling

2. Diamond stones

3. Tungsten carbide burs

4. Twist drills

5. Diamond burs

MANAGEMENT OF DAMAGED

TEETH

Depends on : a. Amount of damage

b. Location of damage

Golden rules of management of

damaged teeth:a. Protecting the vital core

b. Avoiding excessive reduction

Approaching the damaged vital teeth

1. Evaluate the condition of the pulp and

periodontal tissues and make a preliminary

decision on the design of the restoration.

2. Remove all caries and old restorations.

3. Reevaluate the strength of the remaining walls

and decide on the final preparation design

4. Execute the chosen design.

PULPAL CONSIDERATION

# Capping

# Pulpotomy

# Pulpectomy

PERIODONTAL CONSIDERATION

CARIES CONTROL

REVALUATION

PROTECTION OF REMAINING TOOTH STRUCTURE

CONVERTION OF DEFECTS INTO RETENTIVE

FEATURE

• Blocks form

• Orientation of sloping surface

ADDITION OF RETENTION BAR RESSTANCE

FEATURES

Grooves

Pinholes

Core build-up

SOLUTION FOR COMMON PROBLEMS

Over-tapered axial wall

Short axial wall

Undercut in axial wall

Over extended box form

Fractured cusp

One missing cusp

Two missing cusp

ELECTIVE DEVITALISATION

ENDO TREATED TOOTH MANAGEMENT

• Crown

• Dowel core

• Reference: Sorensen and Martin

Hoag and Dwyer

ATYPICAL TOOTH PREPARATION

Teeth that deviate from the anatomical

average or have suffered from carious

attack, erosion or traumatic injury,

sufficient to destroy the outline form of a

typical porcelain veneer crown preparation

will be classified as atypical.

DESIGN FACTORS

Achieving uniform

stress distribution

Retention form

Class 1: Crowns larger than anatomical average.

Class 2: Crowns smaller than anatomical average.

Class 3: Crowns which show marked anatomical deviation from

normal.

Class 4: Crowns with loss of enamel and dentine on either the mesial

or distal surfaces.

Class 5: Crowns with loss of enamel and dentine on both the mesial

and distal surfaces.

Class 6: Crowns with loss of enamel and dentine at the incisal edge,

e.g. traumatic injury or abrasion.

Class 7: Crowns with loss of enamel and dentine at the cervical

margins.

Class 8: Crowns with generalised loss of surface enamel.

Class 9: Length of clinical crown greater than anatomical crown, i.e.

loss of supporting gingival tissue.

TYPES OF ATYPICAL TOOTH PREPARATION

CLASS-1

CLASS-2

• Maxillary lateral

• Mandibular incisor

CLASS-3

Absence of

cingulum

Thin teeth Conical teeth Excess labial

curvature

CLASS-4

Mesial Distal Middle

third

Cervical

third

CLASS-5

CLASS-6

Attrition

Trauma

CLASS-7

CLASS-8

CLASS-9

SUMMARY OF REQUIREMENTS

1.

2. 1. Optimum retention form may be provided for the atypical

preparation by preserving the maximum amount of dentine at the

cervical one third of the preparation. This area should be prepared so

that near parallelism is obtained on both the approximal, lingual and

labial axial walls, thereby ensuring that the crown only has one path of

insertion.

3.

4. 2. Additional retention form and strength may be given to the

porcelain veneer crown by providing an artificial cingulum step in cases

where the tooth preparation would tend to be conical. This cingulum

step will lessen the degree of taper of the lingual surface and bring it

nearer to parallelism with the labial surface.5.

3. Approximal areas of missing tooth structure should not be

entirely restored with cement but should be prepared to form

small lingual steps in the preparation. These steps must be

slightly rounded at all line or point angles and provide an anti-

rotational locking mechanism for the porcelain veneer crown. It

is recommended that high fusing aluminous core porcelain is

used to restore these areas, thereby providing greater strength

than a conventional cement lining. Alternatively the missing

area can be built up with a cast metal coping when a metal-

ceramic crown is fitted.

4. Additional anchorage for the porcelain veneer crown may

be provided by constructing thin gold copings or pinlays which

will restore the missing areas of incisal dentine. The use of

accessory gold anchorage in porcelain veneer crown work is

limited by the amount of space available, and should only be

used as a last resort it a strong and aesthetic result is to be

obtained. The metal-ceramic crown or platinum bonded

alumina crown will often provide more suitable alternatives.

The use of pins with a composite resin core is not satisfactory

on front teeth due to the risk of shearing of the pins or micro-

leakage at the resin tooth interface due to the low modulus of

elasticity and low shear strength of the composite fillings.

MODIFICATION FOR SPECIAL SITUATION

# For Fixed bridge abutment

# For Removable partial abutment Cingulum rest

Occlusal rest

RESIN BONDED BRIDGES

Anterior bridge

Posterior bridge

FIXED PROSTHESIS FOR PERIODONTALLY

COMPROMISED TOOTH

Tooth mobility situation by LINDHE

Situation I – Increased mobility of a tooth with

increased width of the periodontal ligament, but

normal height of the alvealor bone.

Situation II – increased mobility of a tooth with

increased width of the periodontal ligament and

reduced height of the alveolar bone.

Situation III – increased mobility of a tooth with

reduced height of the alveolar bone and normal width of

the periodontal ligament.

Situation IV – Progressive (increasing) mobility of a

tooth (teeth) as a result of gradually increasing width of

the periodontal ligament in teeth with a reduced height

of the alveolar bone.

Situation V – increased bridge mobility despite

splinting.

SPLINTS

Temporary

Intermediate

Permanent

CONNECTORS

Rigid

Non-rigid

TELESCOPIC CROWN

By Peeso in 1916

• Advantages

• Disadvantages

ORTHODONTIC THERAPY

• Occlusal consideration

• Alteration in periodontal environment

OTHER CONSIDIDERATION

• Complete/Partial coverage

• Marginal placement

• Wound healing consideration

• Atraumatic preparation

• Furcation treatment