Fundamentals of cavity Preparation

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INTRODUCTION CAVITY: Refers to a defect in enamel, or enamel & dentin, resulting from pathologic process- DENTAL CARIES Effective treatment for preventing further progress - complete removal of affected area

Needs for Restorations • • • •

Caries Non-carious lesions Replacement of restorations or repair Iatrogenic dentistry

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CAVITY PREPARATION defined as the mechanical alteration of a defective injured or diseased tooth in order to best receive a restorative material which will re-establish a healthy state for the tooth including esthetic corrections, along with normal form and function.

Objectives of Tooth Restorations 1. To restore form/function and esthetics, if possible 2. To promote maintenance of integrity of hard and soft tissues of the oral cavity 3. To promote health and welfare of patients

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Objectives of Cavity Preparation 1. To remove all defects and give necessary protection to the pulp 2. To locate the margins of the restorations as conservatively as possible 3. To form the cavity so that under the masticatory forces the tooth and the restoration will not fracture and the restoration will not be displaced 4. To allow for the esthetic and functional placement of a restorative material 6

Definition of Cavity Preparation • Mechanical alteration of a tooth to receive a restorative material which will return the tooth and area to proper form, function, and esthetics • Preparation procedure includes all defective and friable tooth structure

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What factors do we have to consider in cavity preparation for successful restorations? • Type of dental restorative material: physical and biological properties • Tooth: location vs. masticatory forces

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FACTORS AFFECTING CAVITY PREPARATION ™ GENERAL FACTORS

™ PATIENTS FACTOR

• • • • •

• economic status • age • choice of material

diagnosis prevention interception preservation restoration

G V BLACKS CLASSIFICATION 9First classification 9universally accepted 9based on type of treatment & areas involved 9controlled by number of factors • • • • • •

to gain access & visibility removal of affected dentin from floor room for restorative material extension for prevention mech. Interlocking retentive designs cavosurface margins self cleaning areas

G V BLACK’S CLASSIFICATION CLASS I ¾pit & fissure ¾occlusal surfaces - premolars & molars ¾lingual surfaces of maxillary incisors

CLASS II ¾proximal surfaces of posterior teeth

CLASS III ¾proximal surfaces of anterior teeth do not involve the incisal edge

CLASS IV ¾proximal surfaces of anterior teeth involve incisal edge

CLASS V ¾gingival third of facial or lingual surfaces

CLASS VI ¾ incisal edge of anterior / occlusal cusps heights of posterior teeth ¾

Simon - later added

OPERATING SITE moist- free environment isolation protecting soft tissues margins limited to supragingival sulcus

Intra-coronal Cavity Preparation

Principles of Cavity Preparation 1. Outline form 2. Resistance form: resistant to tooth and restoration fracture and displacement of restoration 3. Retention form: prevent from dislodging of restoration 4. Convenience form: access for caries removal, band insertion, etc 5. Remove remaining carious lesions 6. Finish margin of enamel walls 7. Perform the toilet of the cavity 25

INITIAL CAVITY PREPARATION extension & initial design of external walls of preparation at a specific limited depth, provide access to cavity/ defect reach sound tooth structure, resist fracture of restoration/ tooth,forces directed in long axis of tooth & retain restoration no deeper than 0.2mm into dentin - pit & fissure 0.2mm - 0.8mm - smooth suface

OUTLINE FORM & INITIAL DEPTH placing cavity margins in positions will occupy in final preparations except enamel walls & margins preparing initial depth of 0.2 - 0.8mm pulpally of DEJ

PRINCIPLES friable / weakened enamel removed all faults included margins placed in position- good finishing of margins of restoration extension for prevention sufficient enamel & dentin to locate the pulpal & axial walls or prepn.surfaces within 0.5mm from DEJ

FACTORS

extent of carious lesion, defect/ faulty restorations esthetic considerations occlusal relationships adjacent tooth structure cavosurface margin

FEATURES preserving cuspal strength preserving marginal ridge strength minimizing f-l extensions enameloplasty connecting to close faults restricting depth

Principles of Cavity Preparation 1. Outline form 1. Cover all carious lesions 2. No extension for prevention

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PRIMARY RESISTANCE FORM

defined as the shape & placement of the cavity walls best enables both restorations & the tooth to withstand, without fracture , masticatory forces delivered in long axis of tooth architectural form given to a tooth , which enables both restoration & remaining tooth to resist structural failure from occlusal loading stresses

Principles of cavity preparation 2. Resistance form 1. Depth- 0.5 mm below DEJ (about 1.5 mm from the deepest pit) 2. Flat floor 3. No unsupported enamel (undermined) 1. Cavosurface margin: 90 degree 2. Angle of departure: 90 degree

4. Slightly-rounded internal line angle 5. Preserve marginal ridge if possible 33

PRINCIPLES ¾ utilize box shape with a flat floor ¾ restrict extension of external walls ¾ slight rounding of internal line angles - reduce stress ¾ cap weak cusps & envelope / include enough weakened tooth ¾ provide enough thickness of restorative material - prevent fracture

¾major principle is that restoration should rest on flat sound tooth structure, perpendicular to occlusal forces directed parallel to the long axis of tooth

FEATURES ¾ relatively flat floors ¾ box shape ¾ includes weakened tooth structures ¾ preservation of cusps & marginal ridges ¾ rounded internal line angles ¾ adequative thickness of restorative materials ¾ seats on sound dentin peripheral to excavation of infected dentin ¾ reduction of cusps for capping

Flat Floor Relatively parallel to the cusp tips

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Cavosurface Margin

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– amalgam -90 degree – inlay beveled- 20-40 degree – margins located on self-cleansing areas – smooth curves

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Prepared Cavity Walls Sharp definite cavosurface margin

E DEJ D

Definite slightly-rounded internal line angle

1. 2. 3. 4.

Cavosurface margin Enamel wall Dentinoenamel junction (DEJ) Dentin wall 39

Undermined Enamel or Overhanged Enamel • Cavity preparation -> walls of cavity should be parallel to directions of enamel rods as much as possible.

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Undermined Enamel

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Principles of Cavity Preparation 3. Retention form Retention form : ¾ shape / form of prepared cavity that resists displacement / removal of restoration from tipping/ lifting forces ¾ defined as a form given to tooth prepn.,especially its detailed anatomy & general shape, which enables the restoration, that will accommodate, to avoid being lodged by masticatory loading 42

¾ intra coronal¾inside a cavity prepn,within the tooth ¾ extra coronal ¾on prepn.surface, replacing reduced ext.tooth

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Principles of cavity preparation 3. Retention form 1. Box form 2. Convergence to occlusal surface (small undercut) 3. Retentive groove 4. Pins and slots 5. Dovetail 6. Acid etching (for resin composite restorations) 44

Retention form 1. Box form

A

2. Convergence to occlusal surface (small undercut)

B

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3. Retention Form Dovetail

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Principles of cavity preparation 3. Retention form Retentive groove Pins

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Retention Slot & Pin

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Principles of Cavity Preparation 4. Convenience form • Convenience form : shape/ form of cavity that

provide adequate observation & accessibility • ease of operation in preparing & restoring the cavity

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FINAL CAVITY PREPARATION Removal of any remaining enamel pit / fissure &/ or infected dentin & / old restorative material, if indicated.

¾it is elimination of any infected carious tooth structure / faulty restoration within the tooth after initial cavity preparation

¾ caries left in pulpal / axial floor excavated ¾ 0.75-1mm of dentin cover the pulp ¾ when affects esthetically ¾ weakened tooth- given retention ¾ secondary caries , if present ¾ periphery of old resto.mate. not intact

PULP PROTECTION

¾pulpal injury, due to ¾heat generated while cutting ¾resto.mat.with good thermal conductivity ¾chemicals from resto.mate. ¾Galvanic currents ¾microleakage

¾placement of cavity liners / bases/varnish– not a step ¾it is the step in adapting the preparation for receiving the final restorative material ¾mechanical, chemical & thermal protection of pulp

SECONDARY RESISTANCE & RETENTION FORM

™TWO TYPES

¾MECHANICAL FEATURES

¾CAVITY WALL CONDITIONING

Mechanical features 9retention locks 9grooves & coves 9skirts 9beveled enamel margins 9pins amalgapins 9slots

¾Cavity wall conditioning features 9enamel, dentinal wall conditioning 9for bonded restorations

FINISHING THE EXTERNAL WALLS OF CAVITY PREPARATION

¾further development when indicated, of a specific cavosurface design & degree of smoothness that produces maximum effectiveness of restorative material being used ¾to create best marginal seal bet.resto.mate.& tooth ¾to afford smooth marginal jn ¾provide maxi.strength of both tooth & resto.

• Features

design of cavosurface margin degree of smoothness of wall

• cavity preparation for – class I amalgam • outline form

class II cavity preparation for amalgam

Class III Cavity Preparation for Amalgam:

Class V Cavity Preparation for Amalgam:

Enameloplasty

It is the removal of a shallow, enamel  developmental fissure or pit to create a  smooth, saucer shaped surface that is self  cleansing or easily cleaned. This is mainly used for smooth surface enamel  defects.

Concepts behind conservative restorations 1. Remove minimum tooth structure required for convenience form 2. Caries removal 3. Access, carving and finishing margins 4. Retention and resistance form

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False conservatism 1. Insufficient convenience form 2. Leaving unsupported enamel 3. Insufficient reduction for restoration strength

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Advantages 1. Reduced risk of pulpal and perio involvement 2. Improved esthetics 3. Less risk of margin and tooth fracture

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Class I Amalgam-preparation design 1. Minimize width of isthmus (1/3 intercuspal distance or less) to reduce risk of tooth fracture. 2. Remove contiguous fissures 3. Rounded internal line angles to facilitate condensation and minimize stresses 4. Minimal pulpal depth is 0.5 mm into dentin from DEJ 5. No need to cross isthmus unless caries is present. 6. If questionable occlusal pits/fissures, consider PRR or sealant 67