Definition (STURDEVANT) : Tooth preparation is the mechanical alteration of a defective,

injured, or diseased tooth to receive a restorative material that re-establishes a healthy state for the tooth, including esthetic corrections where indicated and normal form and function.

TOOTH PREPARATION

INITIAL TOOTH PREPARATION STAGE:

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

FINAL TOOTH PREPARATION STAGE:

Step 5: Removal of any remaining infected dentin and/or old restorative material, if indicated

Step 6: Pulp protection, if indicated Step 7: Secondary resistance and retention forms Step 8: Procedures for finishing external walls Step 9: Final procedures: cleaning, inspecting, sealing

STAGES AND STEPS IN TOOTH PREPARATION

‘Initial tooth preparation is the extension and initial design of the external walls of the preparation at a specified, limited depth so as to provide access to the caries or defect, reach sound tooth structure (except for later removal of infected dentin on the pulpal or axial walls), resist fracture of the tooth or restorative material from masticatory forces principally directed with the long axis of the tooth, and retain the restorative material in the tooth.’

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Sturdevant

INITIAL TOOTH PREPARATION

Step 1: Outline Form and Initial Depth

Step 2: Primary Resistance Form

Step 3: Primary Retention Form

Step 4: Convenience Form

STEPS OF INITIAL TOOTH PREPARATION

OUTLINE FORM AND INITIAL DEPTH

DEFINITIONEstablishing the outline form means:(1) placing the preparation margins in the positions theywill occupy in the final preparation, except for finishingenamel walls and margins

(2) preparing an initial depth of 0.2 to 0.8 mm pulpally of the DEJ position or normal root-surface position (no deeper initially whetherin tooth structure, air, old restorative material, or caries unless the occlusal enamel thickness is minimal and greater dimension is necessary for strength of the restorative material).

PRINCIPLES

1. All friable and/or weakened enamel should be removed.

2. All faults should be included.

3. All margins should be placed in a position to afford good finishing of the margins of the restoration.

Extent of carious lesion, defect or faulty old restoration. Esthetic considerations. Occlusal requirements. Adjacent tooth contour. Cavosurface marginal configuration which varies with

type of restorative material used.

FACTORS DETERMINING OUTLINE FORM

Preserving cuspal strength Preserving marginal ridge strength Minimizing faciolingual extension Using enameloplasty Connecting two close(less than 0.5 mm apart) faults or

tooth preparations Restricting the depth of the preparation into dentin to a

maximum of 0.2 mm for pit-and-fissure caries and 0.2 to 0.8 mm for the axial wall of smooth surface caries

FEATURES

FACTORS CONTROLLING OUTLINE FORM IN PIT-AND-FISSURE LESIONS

The extent to which the enamel has been involved by the carious process

The extensions that must be made along the fissures to achieve sound and smooth margins

The limited bur depth related to the tooth’s original surface while extending the preparationto sound external walls that have a pulpal depth of approximately 1.5 to 2 mm and usually a maximum depth into dentin of 0.2 mm

Extend the preparation margin until sound tooth structure is obtained and no unsupported and/or weakened enamel remains.

Avoid terminating the margin on extreme eminences such as cusp heights or ridge crests.

If the extension from a primary groove includes one half or more of the cusp incline, consideration should be given to capping the cusp. If the extension is two-thirds, the cusp-capping procedure is most often the proper procedure which removes the margin from the area of masticatory stresses.

Extend the preparation margin to include all of the fissure that cannot be eliminated by appropriate enameloplasty.

Rules for establishing outline form for pit-and fissuretooth preparation

Extend the preparation margin to include all of the fissure that cannot be eliminated by appropriate enameloplasty

Restrict the pulpal depth of the preparation to a maximum of 0.2 mm into dentin

When two pit-and-fissure preparations have less than 0.5 mm of sound tooth structure between them, they should be joined to eliminate a weak enamel wall between them.

Outline form should be extended to provide sufficient access for proper tooth preparation, placement of restorations and finishing procedures.

Rule for cusp capping: If extension from a primary groove toward the cusp tip is nomore than half the distance, then no cusp capping; if this extension is from one half to two thirdsof the distance, then consider cusp capping; if the extension is more than two thirds of the distance, then usually cap the cusp.

A, Enameloplasty on area of imperfect coalescence of enamel. B, No more than one-third of the enamel thickness should be removed.

Smooth-surface lesions occur in two very different locations: (1) proximal surfaces or (2) gingival portion of the facial and lingual surfaces

Rules for establishing outline forms for proximal surface tooth preparations (class II, III, and IV):

Preparation margins should be extended until sound tooth structure is obtained and no unsupported and/or weakened enamel remains.

Avoid terminating the margin on extreme eminences such as cusp heights or ridge crests.

Extend the margins to allow sufficient access for proper manipulative procedures. Restrict the axial wall pulpal depth of the proximal preparation to a maximum of

0.2 to 0.8 mm into dentin.

Outline form and initial depth for smooth-surfacelesions.

Provide minimal clearance of 0.5 mm between the gingival margins and adjacent tooth.

Place the facial and lingual margins in proximal preparations into respective embrasures to provide specified clearance between margins and adjacent tooth.

Axial wall should follow the contour of the external tooth surface or the curvature of the DEJ buccolingually and occlusogingivally.

In Class III preparations, the incisal margin may be placed in the area of contact, especially when an esthetic restorative material is used or when the incisal embrasure is not large enough to allow extension incisal of contact and still have a strong incisal angle of the tooth.

FACTORS CONTROLLING OUTLINE FORM OF CLASS V TOOTH PREPARATION: Extent of the lesion (except pulpally)

RULES FOR ESTABLISHING OUTLINE FORM FOR CLASS V LESION:

Extend the preparation mesially, distally, gingivally and occlusally (incisally) till the sound tooth structure is reached.

The axial wall pulpal depth at the gingival wall without an enamel portion should be 0.8 mm

The axial wall pulpal depth at the occlusal wall should be more, i.e. 0.5 mm extension into dentin

GINGIVAL PORTION OF FACIAL AND LINGUAL SURFACES (CLASS V):

DEFINITION (Sturdevant)

Primary resistance form may be defined as the shape and placement of the preparation walls that best enable the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the tooth.

PRIMARY RESISTANCE FORM

To use the box shape with a relatively flat floor, which helps the tooth resist occlusal loading by virtue of being at right angles to the forces of mastication that are directed in the long axis of the tooth

To restrict the extension of the external walls to allow strong cusp and ridge areas to remain with sufficient dentin support

To have a slight rounding of internal line angles to reduce stress concentrations in tooth structure

PRINCIPLES

To cap weak cusps and envelope or include enough of the weakened tooth structure within the restoration in extensive tooth preparations to prevent or resist fracture of the tooth by forces in the long axis and obliquely directed forces

To provide enough thickness to restorative material to prevent its fracture under load

To bond the material to tooth structure when appropriate

FACTORS AFFECTING RESISTANCE FORM

Assessment of the occlusal contact on the restoration and remaining tooth structure.

Amount of remaining tooth structure ( eg. In class IV restorations , the cavity is kept narrow faciolingually to obtain resistance form)

All weakened , friable tooth structure should always be removed.

Enhancement of the resistance form by bonding the restoration to the remaining tooth.

Type of restorative material- The minimum thickness of restorative material required for restoration with :- amalgam 1.5 mm, cast restoration 1 mm ,ceramics 2 mm; to resist fracture.

Occlusal stresses on the tooth ( Greater the occlusal force , the greater is the potential for future fracture)

FEATURES1. Relatively flat floor

2. Box shape

3. Inclusion of weakened tooth structure

4. Preservation of cusps and marginal ridges

5. Rounded internal line angles

6. Adequate thickness of restorative material

7. Reduction of cusps for capping when indicated

Resistance forms must consider resistance of tooth to fracture from forces exerted onrestoration.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

DEFINITION (Sturdevant)

Primary retention form is the shape or form of the conventional preparation that resists displacement or removal of the restoration by tipping or lifting forces.

Although they are separate entities,the same prepared form may contribute to both resistance and retention qualities of the preparation.

PRIMARY RETENTION FORM

PRINCIPLESFor Amalgam restorations :-

In most class I and all class II preparations, the amalgam is retained in the tooth by developing external tooth walls that converge occlusally

Occlusal convergence of the proximal portion helps in conserving the marginal ridges

The cavosurface angle where the proximal facial and lingual surfaces meet the marginal ridge is a desirable 90 degrees because of the occlusal convergence of the preparation

Adhesive systems provide some retention by micromechanically bonding amalgam to tooth structure and reducing or eliminating microleakage.

For Composite restorations :-

Composite restorations are retained in the tooth by a micromechanical bond that develops between the material and the etched and primed prepared tooth surface.

The enamel and dentin are etched by an acid ,and the dentin is primed with a dentin bonding agent before placement of the composite.

Other conventional- type composite restorations may require a separate enamel bevelling procedure that would be done in final tooth preparation.

For Cast Metal restorations :-

Close parallelism of the opposing walls, with small angle of divergence (2-5 degrees) from the line of draw , helps in enhancing retention.

The degree of divergence needed primarily depends on the length of the prepared walls: the greater the vertical height of the walls , the more divergence is permitted , but within the range mentioned.

In class II preparations , an occlusal dovetail may aid in preventing the tipping of the restoration by occlusal forces.

Basic primary retention form in Class II tooth preparationsfor amalgam (A) with vertical external walls of proximaland occlusal portions converging occlusally and for inlay( B) with similar walls slightly diverging occlusally.

DEFINITION (Sturdevant)

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

CONVENIENCE FORM

FEATURES • Obtaining this form may necessitate extension of distal,

mesial, facial or lingual walls to gain adequate access to the deeper portion of the preparation.

• Occlusal divergence of vertical walls in class II cast restorations.

• Extending proximal preparations beyond proximal contacts ie. Proximal clearance of contact area

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