FUNDAMENTALS IN FUNDAMENTALS IN TOOTH PREPARATION TOOTH PREPARATION

Dr. Ramesh BhartiDr. Ramesh BhartiAssistant ProfessorAssistant ProfessorConservative Dentistry &EndodonticsConservative Dentistry &EndodonticsKing George’s Medical University King George’s Medical University Lucknow Lucknow

Definition of Operative Definition of Operative DentistryDentistry

Operative dentistry is the ART and SCIENCE of the diagnosis, treatment, prognosis of defects of teeth which do not require full coverage restorations for correction, such treatments should results in the restoration of proper tooth form, function, and esthetics while maintaining the physiologic integrity of the teeth in harmonious relationship with adjacent hard and soft tissue, all of which enhance the general health and welfare of the patient.

Objectives of Cavity Preparation

Remove all defects and give the necessary protection to pulp.

Locate the margins as conservatively as possible.

Form the cavity so that both the restoration and tooth can withstand the load of mastication.

Allow for the esthetic and functional placement of a restorative material.

Need of RestorationNeed of Restoration

Caries

Malformed, discolored or fractured teeth

Restoration replacement

Factors affecting tooth preparationFactors affecting tooth preparation

1. General Factors Pulpal & periodontal status Occlusal relationship

2.Dental anatomy Direction of enamel rods Thichness of enamel /dentin Size and positionof pulp Relationship of tooth to its supporting tissues

3.Patient factors

Age Esthetic consideration Economic status Patients with high risk caries

4.Affected & infected Dentine

5. Restorative material factors

Cavity preparation Matrix application Preparation of materials Insertion and carving of materials Finishing and Polishing

Approach of Operative. Approach of Operative. cont…..cont…..

Cavity PreparationCavity Preparation

The mechanical alteration of a defective, injured, or diseased tooth in order to best receive a restorative material which will re-establish a healthy state for the tooth including esthetic corrections where indicated, along with normal form and function.

Cavity StructureCavity Structure

walls angles Floor

Classification of cavityClassification of cavity

Class I Class II Class III Class IV Class V Class VI

—G.V.Black in 1908

CavityCavity

Simple cavity: only one tooth surface is involved.

Compound cavity: two surfaces are involved.

Complex cavity: three or more surfaces are involved.

Class 1

Class 2

Class 1

Class 2

Class 3

Class 4

Class 5

Class 6

Stages and Steps in Cavity preparation

•Initial cavity preparation stage

•Final cavity preparation stage

Initial cavity preparation stage

Step 1 Outline form and initial depth

Step 2 Primary resistance form

Step 3 Primary retention form

Step 4 Convenience form

FINAL CAVITY PREPARATION STAGE

Step 5 Removal of any remaining infected

dentin if indicated

Step 6 Pulp protection

Step 7 Secondary resistance & retention form

Step 8 Procedure for finishing external walls

Step 9 Final procedures

Outline Form and Initial Depth

Definition: placing the cavity margins in the positions they will occupy in the final preparation.

preparing an initial depth of 0.2~0.8 mm pulpally of the dentinoenamel junction position or normal root surface position.

Maxillary Class Ⅰ outline form

Mandibular Class Ⅰ outline form

Maxillary Class Ⅱ outline form

Mandibular Class Ⅱ outline form

Common Error

Outline Form and Initial Depth

Principles:

all friable and/or weakened enamel should be removed

all faults should be included

all margins should be placed in a position to afford good finishing of

the margins of the restoration.

Margins of the preparation will be located on finishable, self –cleansing area.

Outline Form and Initial Depth Features:

preserving cuspal strength

preserving marginal ridge strength

minimizing facio-lingual extension

using enameloplasty

connecting two close faults or cavities

restricting the depth of the preparation into dentin.

Auxillary Factors

Conservation Adjacent enamel cracks or

decalcification could be involved in the preparation.

Type of restorative material. Extension for access. anatomy and alignment. If possible, no margins will be in

occlusion with opposing teeth. Esthetics

Outline Form and Initial Depth for pit and fissure cavities

Controlled by three factors1- Extension to which enamel has been involved

by caries.

2- Extension to achieve sound and smooth margins.

3- Limited bur depth while extending the preparaton

Rules

Capping of cusp should be done when cavity extension is two-third from central fissure to cuspal eminence.

Include all fissures that cannot be eliminated by enameloplasty.

Restrict the depth.

Join two lesions if they are less than 0.5 mm apart.

Outline Form and Initial Depth for smooth surface cavities

Extension of cavity. Sufficient access. Depth. Sufficient clearance with adjacent tooth.

Initial cavity preparation stage

Step 1 Outline form and initial depth

Step 2 Primary resistance form

Step 3 Primary retention form

Step 4 Convenience form

Primary Resistance Form Primary Resistance Form

Definition: The shape and placement of the cavity walls

that best enable both the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the the tooth.

Primary Resistance Form Primary Resistance Form

Principles: To utilize the box shape with a relatively flat floor to resist occlusal loading by virtue of being at right angles to mastication force.

To restrict the extension of the external walls (keep as small as possible) to allow strong cusp and ridge areas to remain with sufficient dentin support.

Primary Resistance Primary Resistance Form Form

Principles:To have a slight rounding of internal line angles to reduce stress concentration in tooth structure;The presence of sharp internal line angles in GOLD FOIL resist the movement of the restorationSharp internal line and point angles in dentin serve as convenient “starting” points for compacting of direct gold. To provide enough thickness of restorative material to prevent its fracture under load.

Primary Resistance Form Primary Resistance Form

Feature: Box shape

Relatively flat floors

Inclusion of weakened tooth structure

Preservation of cusps and marginal ridges

Rounded internal line angles

Adequate thickness of restorative materials

Reduction of cusps for capping if indicated

Primary Resistance Primary Resistance cont….cont….

Designing the outline form so that minimal of restoration is exposed to occlusal stress.

Seat on sound dentin.

Vale Experiments

1 MR at 1/4th ICD -10% Loss of FR 2 MR at 1/4th ICD - 15% Loss of FR 1 MR at 1/3th ICD -30% Loss of FR 2 MR at 1/3th ICD -35% Loss of FR 1 MR at 1/2 of ICD -40% Loss of FR 2 MR at ½ of ICD -45% Loss of FR

Initial cavity preparation stage

Step 1 Outline form and initial depth

Step 2 Primary resistance form

Step 3 Primary retention form

Step 4 Convenience form

Primary Retention Form Primary Retention Form

Definition: The shape or form of the prepared cavity

that resists displacement or removal of the restoration from tipping or lifting forces.

Primary Retention Form Primary Retention Form

Principles: depending on the materials Amalgam restoration:

developing external cavity walls that converge occlusally and dovetail design

The devotail design provide retention form to the occlusal portion of the cavity.

The occlusal convergence of the walls offers retention in the proximal portion of the cavity against displacement occlusally.

Primary Retention Form Primary Retention Form

Principles: depending on the materialsComposite restoration:

a mechanical bond between the material

and conditioned, prepared tooth structure.

Dentin etched with 32% phosphoric acid Collagen exposed by the acid.

FIG

Bonding of resin to dentin, using a "total-etch" technique

16 Bonding to dentin using a self-etching primer.

Scanning electron micrograph of the transition betweencomposite resin (C) adhesive (A), adhesive-hybrid layer(H), and hybrid layer-dentin.

Initial cavity preparation stage

Step 1 Outline form and initial depth

Step 2 Primary resistance form

Step 3 Primary retention form

Step 4 Convenience form

Convenience Form Convenience Form

Conception: The shape or form of the cavity that

provides for adequate observation, accessibility, and ease of operation in preparing and restoring the cavity.

Convenience Form Convenience Form

Principles:

Allow access for caries removal Allow access for restoration placement Allow access to margins for finishing,

evaluation and cleaning

Convenience Form

Final cavity preparation stage

Step 5 Removal of any remaining infected

dentin if indicated

Step 6 Pulp protection

Step 7 Secondary resistance & retention form

Step 8 Procedure for finishing external walls

Step 9 Final procedures

Removal of any remaining infected Removal of any remaining infected dentin if indicateddentin if indicated

Definition: The elimination of any infected

carious tooth structure or faulty restorative material left in the tooth after initial cavity preparation.

Removal of dentinal caries using round burs and spoon excavators

Pulp protectionPulp protection

Using liners or bases to protect the pulp or to aid pulpal recovery or both.

If the infected dentin more than 2 mm deeper from the initial pulpal or axial wall then a Liner is indicated.

Final cavity preparation stage…..

Step 5 Removal of any remaining infected

dentin if indicated

Step 6 Pulp protection

Step 7 Secondary resistance & retention form

Step 8 Procedure for finishing external walls

Step 9 Final procedures

Secondary resistance and Secondary resistance and retention forms retention forms

Most compound and complex cavity preparations require additional resistance and retention form.

The exception being those preparations that are very conservative.

Secondary resistance and Secondary resistance and retention forms retention forms

Mechanical forms

Cavity wall conditioning form

Mechnical form:

Proximal locks

Proximal slots

Proximal locks

Slot on gingival wall

Final cavity preparation stage….

Step 5 Removal of any remaining infected

dentin if indicated

Step 6 Pulp protection

Step 7 Secondary resistance & retention form

Step 8 Finishing external walls

Step 9 Final procedures

Finishing the external walls Finishing the external walls

Definition: Finishing the preparation walls is

the further development of a specific cavosurface design and degree of smoothness that produces the maximum effectiveness of the restorative material being used.

Finishing the external walls Finishing the external walls

Objectives: To create the best marginal seal possible

between the restorative material and tooth structure;

To afford a smooth marginal junction; To provide maximum strength of both the

tooth and the restorative material at and near the margin.

The strongest enamel margin is that margin which is composed of full-length enamel rods that are supported on the cavity side by shorter enamel rods, all of which extend to sound dentin.

Finishing the external walls Finishing the external walls

The design of the cavosurface angle

The degree of smoothness of the wall

The design of the cavosurface angle depending on the material:

Amalgam: 90°

Composite: beveling 30°~ 40°

Final cavity preparation stage……..

Step 5 Removal of any remaining infected

dentin if indicated

Step 6 Pulp protection

Step 7 Secondary resistance & retention form

Step 8 Procedure for finishing external walls

Step 9 Final procedures

Final proceduresFinal procedures

cleaning inspecting varnishing conditioning

Multiple Choice Questions

Q.1. In cavity prepartion cavo-surface margin will be a junction between :

a) Cavity wall/floor and adjacent tooth surface.

b) Cavity wall and floor.c) Floor of the occlusal box and aproximal

boxd) Axial wall and occlusal floor.

Q.2 Toilet of the cavity is: a) Removal of debris by washing with

water b) Removal of debris by cold air c) Removal of debris by hot air d) Washing the cavity with water.

Q.3 Most common fracture seen in amalgam restoration at:

a) Cavosurface margin. b) Contact area c) Isthmus area d) Proximal box

Q 4 G. V Black concluded that following area of tooth surface are relatively non-selfcleansing:

A) Pit and fissures B) Tips and cusps C) Fossa D) Marginal ridge

Q.5 Class III amalgam restorations areusualy prepared on:

a) Distal surface of anterior teeth b) Mesial surface of canine c) Distal surface of canine c) Mesial and distal surface of all teeth.