FUNDAMENTALS OF TOOTH PREPARATION

DR ASMA NAWAZ CHANNA

TOOTH PREPARATION

It is the mechanical alteration of defective, injured or diseased tooth to receive a restorative materials that reestablished a healthy state for tooth including esthetic correction where indicated and normal form and functions

CONVENTIONAL TOOTH PREPARATION Preparations that require specifics

wall forms,depths and marginal form owing to the properties of the restorative materials

E.g 1 amalgam 2 gold 3 ceramic

MODIFIED TOOTH PREPARATION Preparations that needs less

specifics depth,and wall and marginal form

E.g 1 composite 2 GIL

OBJECTIVES OF TOOTH PREPARATIONS No friable tooth structure can be

left All faults or carries is removed Remaining tooth structure is left

as strong as possible and should be supported by sound dentine

Underlying pulpal tissue is protected where indicated

Restorative materials is retained in a strong, esthetic and fundamental manners

NEED FOR RESTORATION

To repair a tooth after destruction from carious lesion

Replacement or repaired of restorations with serious defects such as gingival excess, defective open margins or poor esthetics

For fructure teeth ,to restore proper form and funtion

PRINCIPALS OF CAVITY PREPARATION Outline form Resistance and retention form Convenience form Removal of remaning carious

dentine Finishing of the enamel walls

and margins toilel of cavity

TOOTH PREPARATION TERMINOLOGYSimple, compound, complex 1. Simple:A tooth preparation is termed simple if only one tooth

surface is involved. 2. Compound: Two surfaces are

involved. 3. Complex: preparation

involving three or more surface

Tooth preparation walls:

Internal wall: prepared surface that does not extend to the external tooth surface

Axial wall: internal wall parallel with the long axis of the tooth

Pulpal wall: internal wall that is perpendicular to the long axis of the tooth

External wall: prepared(cut) surface that extend to external tooth surface

Floor: prepared wall that is reasonably flat and perpendicular to the occlusal forces that are directed occlusogingivally.

Externalwalls:

I nternalwalls:

Tooth preparation angles

Line angle: the junction of two planal surface of different orientations along a line.

Point angle: the junction of three planel surface of different orientation

Cavosurface angle

Cavosurface angle is the angle of the tooth structure formed by the junctions of the prepared walls and the external surface of the tooth

STAGES AND STEPS OF TOOTH PREPARATIONS Initial cavity preparation stages

final cavity preparation stages:

Initial cavity preparation stages

Step 1:Outline form and initial depthStep 2:Primary resistance formStep 3:Primary retention formStep 4:Convenience form

Step 1:Outline form and initial depth 1. placing the preparation margins in

the positions that will occupy in the final preparation except for finishing walls and margins

2.initial depth should be .2 to.8 pulpaly of DEJ (fig 6-1)

Principles:

Step 2:Primary resistance form Defined as the shape and placement

of the preparation wall that best enable the restoration and tooth to with stand without fructure during masticatry forces delivered principally in the long axis of the tooth

Resistance forms must consider resistance of tooth to fracture from forces exerted on restoration. Flat floor (A) will help prevent restoration movement, whereas rounded pulpal floor( B) may allow a nonbonded restoration rocking action producing a wedging force, which may result in shearing of tooth structure.

Principles:1.To use box shape with a

relatively fiat floor which help the tooth to resist occlusal loading during masticatory forces

2.internal line angles shoulid be round to reduce stress concentration in tooth stucture

3.To provide enough thickness to restorative material to prevent its fructure under loading

Step 3:Primary retention formPrimary retention form is the

shape or form of conventional preparation that resist displacement or removal of the restoration by tipping or lifting forces

Principles: principles of primary retention

form vary depending on the materials

E.G For amalgam external walls should be

converge occlusaly

Step 4: Convenience Form

Convenience form is that shape or form of the preparation that provides for adequate observation, accessibility, and ease of operation in preparing and restoring the tooth.

final cavity preparation stages:

Step 5:removal of any remaining carious or infected dentine

Step 6:pulp protection if indicatedStep 7:secdondary resistance and

retention form Step 8:finishing of the external wallsStep 9:cleaning,inspecting and sealing