Principles of Tooth Preparation PDF

Principles of Tooth Preparation Capter 7 Assist. Prof. Dr. Raşa İmranoğlu PURPOSE OF TOOTH PREPARATION Preventing and treating caries Dental caries is one of the most common disease affect- ing approximately 80 percent of the population in devel- oped countries The aim of prevention and treatment...

Principles of Tooth Preparation Capter 7 Assist. Prof. Dr. Raşa İmranoğlu PURPOSE OF TOOTH PREPARATION Preventing and treating caries Dental caries is one of the most common disease affect- ing approximately 80 percent of the population in devel- oped countries The aim of prevention and treatment is to maintain a functioning set of teeth. Interventions can halt and even reverse the development of caries. Replacing Restorations Treatment of Malformed, Fractured and Traumatized Teeth Esthetic Improvement Restoration of Tooth Material Loss TYPES OF RESTORATION • Tooth restoration may be classified as intracoronal, when it is placed within a preparation made in the crown of a tooth or extracoronal, when it is placed outside the tooth as in the case of a crown. Intracoronal restoration is placed directly into the tooth preparation while extracoronal restoration uses an indirect technique. • The materials used to restore teeth are: dental amalgam, composite resin, glass ionomer cement, resin-modified glass ionomer cement, compomer and cermet, cast gold and other alloys, and porcelain. Tooth factors • Factors to be considered before restoration of a tooth • Primary or permanent • Occlusal stresses • Quality of tooth (hypoplasia) • Location of tooth • Type of tooth • Type of tooth preparation. • Patient’s exposure to fluoride General patient factors • Age • Xerostomia • Socioeconomic status • Diet • Caries status • General health • Presence of any parafunctional habit. Factors related to clinicianand the restoration to be used 1.Factors related to clinician and the restoration to be used 2. Type of restoration 3. Physical properties of the restoration 4. Whether moisture control can be achieved or not 5. Technical expertise. TERMINOLOGY OF TOOTH PREPARATION 1.Tooth Preparation It is the mechanical alteration of a defective, injured or diseased tooth in order to best receive a restorative material which will re-establish the healthy state of the tooth including esthetics correction when indicated along with normal form and function Tooth Preparation Walls • Internal Wall It is a wall in the preparation, which is not extended to the external tooth surface • External Wall • An external wall is a wall in the prepared tooth that extends to the external tooth surface .External wall takes the name of the tooth surface towards which it is situated. • Pulpal Wall A pulpal wall is an internal wall that is towards the pulp and covering the pulp. It may be both vertical and perpendicular to the long axis of tooth. • Axial Wall It is an internal wall which is parallel to the long axis of the tooth • Floor Floor is a prepared wall which is usually flat and perpen- dicular to the occlusal forces directed occlusogingivally, for example, pulpal and gingival walls • Internal Wall It is a wall in the preparation, which is not extended to the external tooth surface • External Wall • An external wall is a wall in the prepared tooth that extends to the external tooth surface .External wall takes the name of the tooth surface towards which it is situated. • Pulpal Wall A pulpal wall is an internal wall that is towards the pulp and covering the pulp. It may be both vertical and perpendicular to the long axis of tooth. • Axial Wall It is an internal wall which is parallel to the long axis of the tooth • Floor Floor is a prepared wall which is usually flat and perpen- dicular to the occlusal forces directed occlusogingivally, for example, pulpal and gingival walls Floor Floor is a prepared wall which is usually flat and perpen- dicular to the occlusal forces directed occlusogingivally, for example, pulpal and gingival walls Cavosurface Angle Margin/Tooth Preparation Margin • Cavosurface angle is formed by the junction of a prepared tooth surface wall and external surface of the tooth • The cavosurface angle may differ with the location of tooth and enamel rod direction of the prepared walls and also differ according to the type of restorative material to be used • Line Angle • It is a junction of two surfaces of different orientations along the line and its name is derived from the involved surfaces. • Point Angle • It is a junction of three plane surfaces or three line angles of different orientation and its name is derived from its involved surfaces or line angles. NUMBER OF LINE ANGLES AND POINT ANGLES IN DIFFERENT TOOTH PREPARATION DESIGNS Type of tooth preparation Line angles Point angles Class I 8 4 Class II 11 6 Class III 6 3 Class IV 11 6 Class V 8 4 Class I Tooth Preparation • For simple class I tooth preparation involving only occlusal surface of molars eight line angles and four point angles are named as follows • Line Angles • Mesiobuccal line angle Point Angles • Mesiobuccopulpal point angle • Mesiolinguopulpal point angle • Distobuccopulpal point angle • Distolinguopulpal point angle. • Mesiolingual line angle • Distobuccal line angle • Distolingual line angle • Faciopulpal line angle • Linguopulpal line angle • Mesiopulpal line angle • Distopulpal line angle Class II Tooth Preparation • For class II preparation (mesio-occlusal or disto-occlusal) 11 line angles and 6 point angles are as follows 1.Line Angles 1.Point Angles • Distofacial • Faciopulpal • Axiofacial • Faciogingival • Axiogingival • Linguogingival • Axiolingual • Axiopulpal • Distolingual • Distopulpal • Linguopulpal. • Distofaciopulpal point angle • Axiofaciopulpal point angle • Axiofaciogingival point angle • Axiolinguogingival point angle •Axiolinguopulpal point angle •Distolinguopulpal point angle. Class III Tooth Preparation 1. For class III preparation on anterior teeth 6 line angles and 3 point angles are as follows. Line Angles • Faciogingival • Linguogingival • Axiogingival • Axiolingual • Axioincisal • Axiofacial. Point Angles • Axiofaciogingival point angle • Axiolinguogingival point angle • Axioincisal point angle. Class IV Tooth Preparation . Line Angles • Faciogingival • Linguogingival • Mesiofacial • Mesiolingual • Mesiopulpal • Faciopulpal • Linguopulpal • Axiogingival • Axiolingual • Axiofacial • Axiopulpal. Point Angles • Axiofaciopulpal point angle • Axiolinguopulpal point angle • Axiofaciogingival point angle • Axiolinguogingival point angle • Distofaciopulpal point angle • Distolinguopulpal point angle. Class V Tooth Preparation • Line Angles • Axiogingival • Axioincisal • Axiomesial • Axiodistal • Mesioincisal • Mesiogingival • Distoincisal • Distogingival. Point Angles • Axiodistogingival point angle • Axiodistoincisal point angle • Axiomesiogingival point angle • Axiomesioincisal point angle. 1.Black gave following guidelines for tooth preparation TOOTH PREPARATION 1. Providing definite mechanical retention in the preparation 2. Extension of preparation in adjacent pits an dfissuresfor 3. prevention of recurrent caries 4. Removal of infected and affected dentin from all surfaces 5. Removal of even healthy tooth structure to gain access and good visibility • When Black gave classification, following conditions and considerations were prevalent at that time: GV BLACK • Poor oral hygiene habits • Poor properties of the existing restorative materials • The expected longer life of the restoration • Hard and fibrous food • Low consumption of refined carbohydrates • More liking towards gold and silver fillings in teeth • Prevailing common diagnostic aids such as PMT. Nowadays because of change in following conditions cavities are prepared more conservative Use of preventive measures like fluoridation of water supply, fluoride toothpaste, topical fluoride applications, proper brushing and flossing, etc. Understanding of the fact that the remineralization of enamel and affected dentin can take place Advances in tooth colored, adhesive, fluoride releasing restorative materials Newer advancements in restorative materials Improvements in diagnostic aids Better oral hygiene maintenance Mechanicalretentionformsfurtherimprovetheretention. GV BLACK CARİES STEPS IN TOOTH PREPARATION •Stage I: Initial tooth preparation steps Outline form and initial depth Primary resistance form Primary retention form Convenience form. •Stage II: Final tooth preparation steps • Removal of any remaining enamel pit or fissure, infect- ed dentin and/or old restorative material, if indicated • Pulp protection, if indicated • Secondary resistance and retention form • Procedures for finishing the external walls of the tooth preparation • Final procedures: Cleaning, inspecting and sealing Under special conditions these sequences are changed. OUTLIİNE FORM GV BLACK CAVİTY PREPERATİON • “Extension for prevention means “placing the margins of preparations at areas that would be cleaned by the excursions of food during chewing” • Margins of the restoration are placed on line angles of the tooth • Occlusal surface is extended through pits and fissures • Proximal line angles extended buccally and lingually through embrasures and cervically below the gingival margin • Advantages • Prevents recurrence of decayinthetoothsurfaceadjoin- ing restoration Results in self-cleaning embrasure areas • Results in self cleaning embrasure • This principle has changed to “Prevention of extension” due to: GV BLACKİS NO LONGER USED • Natural remineralization (via calcium and phosphate from saliva) • Fluoride induced remineralization (through water, dentifrices, restorative materials). • Advancements in instrumentation • Advancements in restorative materials • Modifications in tooth preparation designs KEEP IN MIND Following principles are kept in mind while preparing an outline form: • 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. Features for establishing a proper outline form are • Preserving cuspal strength • Preserving strength of marginal ridge • Minimizing the buccolingual extensions • If distance between two faults is less than 0.5 mm, connect them • Limiting the depth of preparation 0.2 to 0.8mm into dentin • Using enameloplasty wherever indicated PREPERATİON • External outline form: It should consist of smooth curves, straight lines and rounded line and point angles • Internal outline form: It includes the relationship of occlusal walls from cavosurface angle to the pulpal floor. Unnecessary loss of tooth structure should be avoided from the inner dimensions of the preparation. • The preparation depth should be at least 1.5 to 2.0 mm vertical from the cavosur- face margin to the pulpal floor and at least 0.2 to 0.5 mm in dentin so as to provide adequate strength to resist fracture due to masticatory forces Outline form for smooth surface lesions—Outline form of proximal caries (Class II, III and IV lesions): Class II are generally diagnosed using bitewing radiographs. Outline form should include all the carious lesion and undermined enamel It should be noted that a proximal lesion which appears to be 2/3 or more toward the dentin has actually penetrated the denti-noenamel junction. Outline form should include all carious lesion WHATCH IT • https://www.youtube.com/watch?v=prOP05wL4zM 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 the long axis of the tooth. • Factors affecting resistance form 1. Amount of occlusal stresses 2. Type of restoration used 3. Amount of remaining tooth structure. Type of restoration Minimum occlusal thickness Cast metal 1–2 mm Amalgam restorations 1.5 mm Ceramics 2 mm • 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 • Consideration to cusp capping depending upon the amount of remaining tooth structure. • 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. Primary Retention Form • Factors affecting retention form are • 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 Retention form for different restorations Amalgam: Retention is increased in amalgam restoration by the following: 1– Providing occlusal convergence (about 2–5%) of the dentinal walls towards the tooth surface 2– Giving slight undercut in dentin near the pulpal wall 3– Conserving the marginal ridges 4– Providing occlusal dovetail Primery retention form Restoration Primary retention form Amalgam class I and II • Occlusal convergence of external walls (about 2–5%) • Conservation of marginal ridges • Occlusal dovetail Amalgam class III and IV • As the external walls diverge outward, reten- tion grooves/coves are the primary retention forms Cast metals • Parallel longitudinal walls with slight occlusal divergence of 2–5°. • Occlusal dovetail • Secondary retention in the form of coves, •skirts and dentin slot Composites • Micromechanical bonding between etched and primed surface with composites • Enamel bevels Direct filling gold • Elastic compression of dentin and starting point in dentin provides retention 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 of convenience form • Sufficient extension of distal, mesial, facial or lingual walls 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. • Proximal clearance is provided from the adjoining tooth during class II tooth preparation. • To make Class II tunnel preparation, for convenience, the proximal caries in posterior teeth is approached through a tunnel initiating from the occlusal surface and ending on carious lesion on the proximal surface without cutting the marginal ridge. • In tooth preparation for cast gold restorations occlusal divergence is one of the feature of convenience form. • The remaining carious portion should be removed only after the initial tooth preparation has been completed because it allows optimal visibility and convenience form for removal of remaining carious lesion. • Coves are small conical depressions prepared in healthy dentin to provide additional retention. • Slots or internal boxes are 1.0 to 1.5 mm deep box like grooves prepared in dentin to increase the surface area. These are prepared in occlusal box, buccoaxial, linguo- axial and gingival walls. Class I Tooth Preparation • Initial Tooth Preparation • The outline form for the Class I occlusal amalgam tooth preparation should include only the defective occlusal pits and fissures (in a way that sharp angles in the marginal outline are avoided). The ideal outline form for a conservative amalgam restoration • • • • • • • • Extending around the cusps to conserve tooth structure and prevent the internal line angles from approaching the pulp horns too closely Keeping the facial and lingual margin extensions as minimal as possible between the central groove and the cusp tips Extending the outline to include fissures, placing the margins on relatively smooth, sound tooth structure Minimally extending into the marginal ridges (only enough to include the defect) without removing dentinal support Eliminating a weak wall of enamel by joining two outlines that come close together (i.e., <0.5 mm apart) Extending the outline form to include enamel undermined by caries Using enameloplasty on the terminal ends of shallow fissures to conserve tooth structure Establishing an optimal, conservative depth of the pulpal wall A punch cut is performed by orienting the bur such that its long axis parallels the long axis of the tooth crown n posterior teeth, the approximate depth of the DEJ is located at 1.5 to 2 mm from the occlusal surface. As the bur enters the pit, an initial target depth of 1.5 mm should be established Depending on the cuspal incline, the depth of the prepared external walls is 1.5 to 2 mm • Distal extension into the distal marginal ridge to include a fissure or caries occasionally requires a slight tilting of the bur distally (≤10 degrees). • This creates a slight occlusal divergence to the distal wall to prevent undermining the marginal ridge of its dentin support • he mesial and distal walls are parallel to the long axis of the tooth crown • The conservative Class I tooth preparation should have an outline form with gently flowing curves and distinct cavosurface margins. • A faciolingual width of no more than 1 to 1.5 mm and a depth of 1.5 to 2 mm are considered ideal, but this goal is subject to the extension of the caries. • The pulpal floor, depending on the enamel thickness, is almost always in dentin The primary resistance form is provided by the following: • Sufficient area of relatively flat pulpal floor in sound tooth structure to resist forces directed in the long axis of the tooth and to provide a strong, stable seat for the restoration • Minimal extension of external walls, which reduces weakening of the tooth • Strong, ideal enamel margins • Sufficient depth (i.e., 1.5 mm) that results in adequate thickness of the restoration, providing resistance to fracture and wear Final Tooth Preparation The final tooth preparation includes removal of remaining defective enamel and infected dentin on the pulpal floor; (2) pulp protection, where indicated; (3) procedures for finishing the external walls; and 4) final procedures of cleaning and inspecting the prepared tooth. The use of desensitizers or bonding systems is considered the first step of the restorative technique. CLASS I Definition of class III and IV cavity Class III located on the proximal surface of anterior teeth Class IV located on the proximal surface of anterior teeth and involve the incisal edge Cavity designe • Conventional cavity preparation • Beveled conventional • Minimal invasive (modified) Cavity preparation Conventional cavity preparation Indication preparation is necessery on the root surface Cavity forming features:     Box shape depth: 0,75mm on root, 0,2mm in dentin 90° cavosurface margin is requied Groove retention can be prepared 0,25mm into the dentin of the axiogingival line and incisoaxial line  dovetail extension Cavity preparation Beveled conventional Indication • replacing an existing defective restoration in the crown • Cavity forming features: • Similar to conventional, but beveled enamel margin • Box shape • 0,75- 1,25 mm depth • 0,2 mm in the dentin • axial wall in convex, following the external contour of the tooth Cavity preparation • Reason of beveling is the microretention • The end of enamel rods are more effectively etched producing deeper „microundercuts” than when only the sides of enamel rods are etched • The composite filling has stronger adhesion to the tooth structure • Better esthetic • Use diamond bur 45 degrees to the external tooth surface • Width should be 0,25-0,5mm Cavity preparation • Minimal invasive • Indication • small and moderate lesions or faults • Cavity forming features • designed to be as conservative as possible • walls extent only of the fault or defect area • no specific shapes or forms • no groove retention • but bevel the enamel Facial or lingual entry ? • Lingual approach is preferable • The facial enamel is conserved for enhanced aesthetics. • Some unsupported enamel may be left on the facial wall • Colour matching of the composite is not as critical • Indications for a facial approach include • The carious lesion is positioned facially • The teeth are irregularly aligned, making lingual access undesirable • An extensive carious lesion extends onto the facial surface