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Steps Of Cavity Preparation
 

Steps Of Cavity Preparation

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In detail of various steps to be followed for cavity preparation...

In detail of various steps to be followed for cavity preparation...

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    Steps Of Cavity Preparation Steps Of Cavity Preparation Presentation Transcript

    • STEPS OF CAVITY PREPARATION MADE BY: ABHINAV FINAL YEAR 2010-2011
    • DEFINITION OF CAVITY PREPARATION Cavity preparation is the mechanical alternation of a tooth to receive a restorative material , which will return the tooth to proper anatomical form , function , and esthetics . The procedure of the preparing the tooth is the removal of the defective or friable tooth structure. Any remaining infected or friable tooth structure may result of further carious progression, sensitivity or pain or fracture of the tooth and/restoration.
    • OBJECTIVES OF CAVITY PREPARATION To remove diseased tissue as necessary and at the same time provides the protection to the pulp.  To locate the margins of the restoration as conservative as possible.  To ensure the cavity form , it should not be under the force of mastication of the tooth.  To allow the functional placement of the restorative material. 
    • PRINCIPLES OF CAVITY PREPARATION  Gain access to caries.  Removal of all carious lesions.  Cut away all significantly unsupported enamel.  Extended margins so that they are accessible for instrumentation and Cleaning.
    • CLASSIFICATION (G.V. BLACK CLASSIFICATION) Black suggested that it was necessary to  Remove additional tooth structure to gain access and visibility.  Remove all trace of demineralized enamel and dentin from the floor , walls and margins of the cavity.  Make room for the insertion of the restorative material sufficient bulk to provide strength.  Provide mechanical interlocking retentive designs.  Extend the cavity to self-cleansing areas to avoid recurrent caries.
    • CLASS I The lesions involving the occlusal surfaces of molars and premolars , the occlusal 2/3 of buccal and lingual surfaces of molars, and the palatal pits in anterior teeth. CLASS II The lesions involving the proximal surfaces of the posterior teeth with access established from the occlusal surface. CLASS III The lesions involving the proximal surfaces of anterior teeth which may or may not involve a labial or a lingual extension & not involving incisal edge.
    • CLASS I CLASS II CLASS III CLASS IV
    • CLASS IV The lesions involving all proximal surfaces of anterior teeth which involves the incisal edge. CLASS V The lesions involving the cervical third of all teeth, including the proximal surface of posterior teeth where the marginal ridge is not included in the cavity preparation. Class VI: Preparations on incisal edges of anterior and cusp tips of posterior teeth without involving any other surfacecome under class VI.
    • CLASS V CLASS VI
    • STEPS IN THE CAVITY PREPARATION (GIVEN BY G V BLACK) A) Stage I Initial Tooth Preparation Steps:  Obtaining Outline Form  Obtaining Primary Resistance Form  Obtaining Primary Retention Form Obtaining Convenience Form B) Stage II Final Tooth Preparation Steps:  Removal of Remaining Carious Dentin   Providing Pulp Protection, If Indicated  Obtaining Secondary Resistance & Retention Form  Finishing of Enamel Walls & Margins  Final Procedures; Cleaning, Inspecting and Sealing
    • OUTLINE FORM AND INITIAL DEPTH  Placing the preparation margins to the place they will occupy in the final tooth preparation except for finishing enamel walls and margins.  Maintaining the initial depth of 0.2 to 0.8 mm into the dentin.  Outline form defines the external boundaries of the preparations.
    • Outline form should include all defective pits and fissures Initial depth of preparation should be 0.2 to 0.8 mm into Outline form should consist of smooth curves, straight lines and rounded line and pointed angles
    • FOLLOWING FACTORS EFFECT THE OUTLINE FORM AND INITIAL DEPTH  Extension of carious lesion.  Proximity of the lesion to other deep structural surface defects.  Relationship with adjacent and opposing teeth.  Caries index of the patient.  Need for esthetics.  Restorative material to be used.  Removal of all weakened and friable tooth structure.
    •  Removal of all undermined enamel.  Incorporate all faults in preparation.  Place all margins of preparation in a position to afford good finishing of the restoration. During tooth preparation, the margins of preparation not only extend into sound tooth tissue but also involve adjacent deep pits and fissures in preparation. This was referred to it as “extension for prevention” by GV Black.
    • EXTENSION FOR PREVENTION Extension for prevention means the placing the margins of preparations at areas that would be cleaned by the excursions of food during chewing. It is done with the objective of preventing the recurrence of caries at the margins of fillings where the recurrence of decay is most commonly seen.
    • PRIMARY RESISTANCE FORM: Definition: Primary resistance form is that shape and placement of preparation walls to best enables both the tooth and restoration to withstand, without fracture the stresses of masticatory forces delivered principally along long axis of the tooth. Factors affecting resistance form:  Amount of occlusal stresses.  Type of restoration used.  Amount of remaining tooth structure.
    • ENAMELOPLASTY Enameloplasty is the careful removal of sharp and irregular enamel margins of the enamel surface by “rounding” or “saucering” it and converting it into a smooth groove making it self-cleansable, finishable and allowing conservative placement of margins
    • FEATURES OF RESISTANCE FORM:  A box-shaped preparation.  A flat pulpal and gingival floor, which helps the tooth to resist occlusal masticatory forces without any displacement.  Adequate thickness of restorative material depending on its respective compressive and tensile strengths to prevent the fracture of both the remaining tooth structure and restoration.
    • Restrict the extension of external walls to allow strong marginal ridge areas with sufficient dentin support.  Inclusion of weakened tooth structure to avoid fracture under masticatory forces.  Rounding of internal line angle to reduce the stress concentration points in tooth preparation 
    • Resistance form also depends upon type of restorative material being used. For example, high copper amalgam requires minimal thickness of 1.5 mm, cast metal requires thickness of 1.0 mm and the porcelain requires a minimum thickness of 2.0 mm to resist fracture. The composite restorations and glass ionomer restorations are more dependent on occlusal wear potential of restorative area and usually require thickness of more than 2.5 mm. (A) Resistance form of tooth provided by flat pulpal and gingival floor, (B) In case of rounded pulpal floor, the rocking motion of restoration results in wedging force which may result in failure of restoration
    • PRIMARY RETENTION FORM Definition: Primary retention form is that form, shape and configuration of the tooth preparation that resists the displacement or removal of restoration from the preparation under lifting and tipping masticatory forces. Usually, resistance and retention forms are obtained by providing same features, hence they are sometimes described together.
    • The common factors affecting retention form are as follows:  Amount of the masticatory stresses falling on the restoration.  Thickness of the restoration.  Total surface area of the restoration exposed to the masticatory forces.  The amount of remaining tooth structure.
    • The retention form is affected by the type of the restorative material used: Amalgam: Retention is increased in amalgam restoration by the following:  Providing occlusal convergence (about 2 to 5%) the dentinal walls towards the tooth surface.  Giving slight undercut in dentin near the pulpal wall.  Conserving the marginal ridges.  Providing occlusal dovetail Preparation walls should have 2°-5° occlusal convergence for amalgam retention Dovetail helps in providing retention Undercut in dentin the helps in retention of
    • Cast metals: Retention is increased in cast restorations by the following:  Close parallelism of the opposing walls with slight occlusal divergence of two to five degrees.  Making occlusal dovetail to prevent tilting of restoration in class II preparations.  Use of secondary retention in the form of coves, skirts and dentin slot.
    • Composites: In composites, retention is increased by:  Micromechanical bonding between the etched and primed prepared tooth structure and the composite resin.  Providing enamel bevels. Direct filling gold:  Elastic compression of dentin and starting point in dentin provide retention in direct gold fillings by proper condensation.
    • CONVENIENCE FORM Definition: The convenience form is that form which facilitates and provides adequate visibility, accessibility and ease of operation during preparation and restoration of the tooth. Features:  Sufficient extension of distal, mesial, facial or lingual walls should be given to gain adequate access to the deeper portion of the preparation.  The cavosurface margin of the preparation should be related to the selected restorative material for the purpose of convenience to marginal adaptation.
    •  In class II preparations access is made through occlusal surface for convenience form.  Provide proximal clearance from the adjoining tooth during class II tooth preparation.
    • STAGE II FINAL TOOTH PREPARATION STEPS REMOVAL OF REMAING CARIOUS DENTIN: After the establishment of external and internal outline form , if any of the remaining carious tooth structure or defective restorative material is left in tooth, it is to be removed in this stage. Infected dentin must be removed even, if it leads to exposure of pulp which is treated accordingly.
    • PULP PROTECTION When remaining dentin thickness is less, pulpal injury can occur because of heat production, high speed burs with less effective coolants, irritating restorative materials, galvanic currents due to fillings of dissimilar metals, excessive masticatory forces transmitted through restorative materials to the dentin and ingress of microorganisms and their noxious products through microleakage. Pulp protection is achieved using liners, varnishes and bases depending upon:  The amount of remaining dentin thickness  Type of the restorative material used.
    • Liners, Varnishes, Bases: Liners and varnishes are used where preparation depth is shallow and remaining dentin thickness is more than 2 mm. They provide:  Barrier to protect remaining dentin and pulp  Galvanic and thermal insulation. Bases are the cements used on pulpal and axial walls in thickness of about 0.5 to 2 mm beneath the permanent restorations. They provide thermal, galvanic, chemical and mechanical protection to the pulp. Commonly used restorative materials as base are zinc phosphate cements, glass ionomers, polycarboxylate cements, zinc oxide eugenol, and calcium hydroxide cement.
    • Secondary Resistance & Retention Form: This step is needed in complex and compound tooth preparations where added preparation features are used to improve the resistance and retention form of the prepared tooth. These are as following: Grooves and coves: Wherever bulk of dentin is present, grooves are prepared without undermining the adjacent enamel. Coves are small conical depressions Grooves are placed in prepared in healthy dentin to provide additional axiofacial and retention. axiolingual so as line angles to increase retention of the restoration
    • Slots or internal boxes: These are mainly used in amalgam restorations. They are 1.0 to 1.5 mm deep box like grooves prepared in dentin to increase the surface area. These are SLOT prepared in occlusal box, buccoaxial, linguoaxial and gingival walls. Locks: Locks are usually prepared for amalgam class II restoration in the proximal or occlusal box of class II
    • Pins: Different types of pins of various shapes and sizes are used to provide additional retention. They can be used in all types of restorations like amalgam, composite and cast restorations. Skirts: Skirts are prepared for providing additional retention in cast restorations. They increase the total surface area of the preparation. Skirts can be prepared on one to all four Skirt in cast restoration sides of the preparation depending upon the required helps in increasing retention retention
    • Amalgampins: Amalgampins are vertical posts of amalgam anchored in dentin. Amalgampins increase the retention and resistance of complete restoration. Beveled enamel margins: Beveling of the preparation margins increases the surface area and thus, the retention in composite restorations. Enamel wall etching: Etching results in microscopic roughness, which increases the surface area and thus
    • Dentin conditioning (etching and priming): Etching and priming of the dentin surface done in some restorative materials increases the retention. Adhesive luting cements: Adhesive luting cements increase the retention of indirect restorations.
    • FINISHING OF ENAMEL WALLS & MARGINS Finishing of the enamel margins should be done irrespective of restorative material used. During finishing there occurs the further enhancement of the cavosurface design and smoothness that produces the maximum adaptation of restoration to the walls and the margins and maximum effectiveness of restoration. The finishing of the preparation walls results in:  Better marginal seal between restoration and tooth structure.  Increased strength of both tooth structure and restoration at and near the margins.  Strong location of the margins.  Increase in degree of smoothness of the margins.
    • Degree of smoothness of walls: It depends upon type of restoration used. For example, for cast metal restorations, a very smooth surface is required whereas for direct gold, amalgam and composite restorations, slight roughness is needed in the preparation walls.
    • Location of the margins: During finishing of the preparation walls and margins, one should follow the principles of paralleling the direction of enamel wall. The knowledge of enamel rods is necessary for proper finishing of the preparation margins. At the margins, all the enamel walls should have full length rods supported by dentin. Features of finished preparation: The design of cavosurface angle depends on type of restorative material being used. For example, for amalgam restoration, cavo-surface angle of 90 degrees affords maximum strength to tooth restoration.
    • FINAL PROCEDURES; CLEANING, INSPECTING AND SEALING The final step in tooth preparation is cleansing of the preparation. This includes the removal of debris, drying of the preparation, and final inspection before placing restorative materials. The debridement of the preparation serves the following objectives:  Cleaning of preparation walls, floors and margins from enamel and dentin chips resulting during tooth preparation: Remove all the debris from the preparation, especially on the margins, otherwise deposits left on them consequently dissolve, resulting in a microleakage which further can result in secondary caries. Cleaning of preparation can be done by using warm water. Immovable particles of debris can be removed with the help of a small cotton pellet dampened with water or hydrogen peroxide.
    • Drying the tooth preparation before insertion of the restorative materials: It can be done using air, dry cotton pellets and commercial cleaners. It is important that teeth are not dehydrated by overuse of air or hot air.  Sterilization of preparation walls using very mild alcohol free disinfectant: Use of mild disinfectant in 