cavity prepration

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DEPARTMENT OF CONSERVATIVE & OPERATIVE DENTISTRY

Presented by: Anjali Arora Roll no.06 BDS final year (Batch2005-06) (Batch2005-

SOME IMPORTANT TERMS :refers to a defect in the tooth enamel or in both enamel & dentin due to carious process.

CAVITY:

Cavity preparation: It is the mechanicalalteration of a defective, injured, or diseased tooth to receive a restorative material that reestablishes a healthy state for the tooth including esthetic corrections where indicated along with normal form and function.

Class I caries

Class II caries

Class III caries

Classification of cavity

Class IV caries

Class V caries

Class VI caries

Walls of cavity preparationInternal walls : surface of prepared cavity that is inside the tooth & does not extend onto the external tooth surface. Its 2 types are: (1) Axial wall internal wall parallel to long axis of tooth. (2) Pulpal wall : internal wall perpendicular to the long axis of tooth & is occlusal to dental pulp. External wall : prepared surface that extends to the external tooth surface. Eg. Facial, mesial, distal, lingual & gingival walls.

Floor or seat : refers to prepared wall that is relatively flat & perpendicular to the occlusal forces which are directed along the long axis of tooth. Enamel wall : that portion of the prepared external wall which is composed of enamel. Dentinal wall : that portion of prepared external wall which is composed of dentin. This wall usually incorporates mechanical retentive features. features.

Angles in cavity preparationLine angle : junction of two walls in a cavity preparation along a definite line. Point angle : junction of three walls in a cavity preparation at a point. Cavosurface angle : angle of the tooth structure formed by the junction of a prepared wall & the external tooth surface.

What determines cavity design ?The structure & properties of the dental tissues. The disease process itself. The properties of restorative material. Occlusal relationships & esthetic needs of the patient. The economic status, age & health of the patient.

Initial cavity preparation stageSTEP STEP STEP STEP 1: 2: 3: 4: Outline form & initial depth. Primary resistance form. Primary retention form. Convenience form.

Final cavity preparation stageSTEP 5: Removing any enamel pit or fissure, infected dentin or old restorative material. STEP 6: Pulp protection. STEP 7: Secondary resistance. STEP 8: Finishing the external walls & margins STEP 9: Final procedures cleaning, inspecting, varnishing & conditioning

STEP 1: OUTLINE FORM AND INITIAL DEPTHDEFINITION:Establishing the outline form means:

placing the preparation margins in the position they will occupy in the final, preparation, except for finishing the enamel walls and margins. preparing an initial depth of 0.20.5mm pulpally beyond the DEJ.

FACTORS:Certain factors affect the decision regarding the extent of the outline form. They are:

1) Extent of the carious lesion, defect or faulty old restoration. 2) Esthetic requirements which may affect the choice of the restorative material and modify the cavity design. 3) Occlusal relationships which may require alterations in the outline form. 4) Contour of the adjacent tooth which may dictate certain modifications to secure proper form and strength. 5) Cavosurface marginal configuration will vary depending on the restorative material employed.

FEATURES: 1) Preserve cuspal strength. 2) Preserve marginal ridge strength. 3) Minimize faciolingual extensions. 4) Use enameloplasty wherever possible. 6) Restrict the depth of the preparation into dentin to a maximum of 0.2-0.5mm.

STEP 2: PRIMARY RESISTANCE FORMDEFINITIONThis is that shape and placement of the cavity walls that best enables both the restoration and the tooth to withstand, without fracture, the masticatory forces delivered principally along the long axis of the tooth.

FEATURESThe following features enhance primary resistance form: Relatively flat floors. Box shape. Including all weakened tooth structure. Preservations of cusps and marginal ridges. Rounded internal line angles. Adequate thickness of the restorative material. Reduction of cusps for capping when indicated.

FACTORSCertain factors affect the resistance form of the preparation: Amount of remaining occlusal contact. Amount of remaining tooth structure. Type of restorative material. Whether or not the restoration can be bonded to the tooth.

STEP 3: PRIMARY RETENTION FORMDEFINITIONThis is that shape or form of the tooth preparation that resists displacement or removal of the restoration tipping or lifting forces. Often features that enhance retention form also enhance resistance form.

PRINCIPLESThe principles of primary retention form vary according to the restorative material: For Amalgam : occlusal dovetail prevent tipping of restoration & occlusal convergence of walls. For Composite : acid etching & bonding ( micromechanical retention) - enamel bevel For cast metal : close parallelism of opposing walls with slight divergence occlusally For direct filling gold : elastic compression of dentin during condensation

Occlusal dovetail prevents tipping of the restoration by occlusal forces.

Occlusal convergence of the preparation walls.

RETENTION FORM

STEP 4: CONVENIENCE FORM

DEFINITION:This is that shape or form of the cavity that provides for adequate observation accessibility ease of operation in preparing restoring the tooth.

FEATURES:Providing adequate width and lateral extensions Refining line and point angles Providing proximal clearance from the adjacent tooth Occlusal divergence for cast gold inlays

STEP 5: REMOVAL OF ANY REMAINING ENAMEL PIT OR FISSURE, INFECTED DENTIN OR DEFECTIVE OLD RESTORATIVE MATERIAL left in the tooth after initial tooth preparation. preparation.PRINCIPLES: The deeper portions of carious dentin may generally exhibit two distinct areas:1.Infected dentin more superficial layer soft and Leathery in consistency light brown in color. high concentration of bacteria and the collagen is irreversibly denatured. 2.Affected dentin deeper layer hard in consistency dark brown in colour. It does not contain bacteria and is reversibly denatured. This layer must therefore be preserved.

This layer is not remineralizable and must therefore be removed.

If infected dentin remains after establishing the pulpal and axial walls during initial tooth preparation, then it has to be eliminated during the final tooth preparation stage.

Infected dentin can be removed by :- spoon excavator -round steel burs at slow speed - slow speed round carbide bur with water coolant.

Ideal method of removing this material would be one in which minimal pressure is exerted, frictional heat is minimized, complete control of the instrument is available. achieved byby use of a round carbide bur, in -high speed hand piece -with air coolant - slow speed complete control of operator on the instrument

Old restorative material removal is indicated if :- it affects esthetics.- compromise retention of new restoration. - evidence of secondary caries. - marginal deterioration of old restoration.

STEP 6 PULP PROTECTIONThis is actually not a step in tooth preparation in the strictest sense it is a step in adapting the preparation for receiving the final restoration it is considered under final preparation stage.

Need for pulp protectionThermal and Mechanical protection

chemical protection

electrical insulation

Need for pulp protection

Barrier to prevent microleakage

Pulp medication to allow pulp recovery in case of deep defects

Pulp ProtectionTraditional linersLiners are volatile or aqueous suspensions or dispersions of zinc oxide or calcium hydroxide that can be applied to a tooth surface in a relatively thin films' Liners provide: Barrier that protects the dentin from noxious agents from either the restorative material or oral fluids, fluids, initial electrical insulation, some thermal protection.

BasesBases are the cements used in thicker dimensions beneath permanent restorations Bases provide : for mechanical, chemical, and thermal protection of the pulp. Examples zinc phosphate; zinc oxide-eugenol; oxidecalcium hydroxide; polycarboxylate;, some type of glass ionomer.

Dycal

The specific pulpal response desired dictates the choice of liner : if removal of infected dentin does not extend deeper than 1 to 2 mm from the initially prepared pulpal or axial wall, usually no liner is indicated. if very deep excavations , pulpal exposures. Calcium Hydroxide Stimulate reparative dentin

Liners and bases in exposure areas should be applied without pressure. approx 1-mm thickness (Calcium Hydroxide ) overlaid with a base for amalgam or cast metal restorations. for composite restorative materials, a liner of calcium hydroxide is indicated only materials, when pulpal exposure or the excavation is judged to be within 0.5 mm of the pulp

If deep excavations ,no pulpal exposures no zinc oxide eugenol liner (except for composite restorations)

Retention groove Slot

SECONDARY RESISTANCE AND RETENTION FORM.

Step- 7

amalgapins.

Beveled enamel margins

ETCHING AND SEALING

SECONDARY RESISTANCE AND RETENTION FORM. Featured as two forms :Mechanical feature include:- retention grooves & coves - groove extensions - skirts - beveled enamel margins - pins, slots, steps & amalgampins

Conditioning procedures :- etching & bonding ( for GIC)

Step 8 :Finishing the external walls of the preparation:Objectives : - provides smooth marginal jun