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Fundamentals of cavity Preparation

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

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Needs for Restorations

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

CAVITY PREPARATIONdefined 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.

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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

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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

FACTORS AFFECTING CAVITY PREPARATION

GENERAL FACTORS

• diagnosis• prevention• interception• preservation• restoration

PATIENTS FACTOR

• economic status • age• choice of material

G V BLACKS CLASSIFICATION

First classificationuniversally acceptedbased on type of treatment & areas involvedcontrolled 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

pit & fissure

occlusal surfaces - premolars & molars

lingual surfaces of maxillary incisors

CLASS II

proximal surfaces of posterior teeth

CLASS III

proximal surfaces of anterior teeth do not involve the incisal edge

CLASS IV

proximal surfaces of anterior teeth involve incisal edge

CLASS V

gingival third of facial or lingual surfaces

CLASS VI

incisal edge of anterior / occlusal cusps heights of posterior teeth

Simon - later added

OPERATING SITE

moist- free environment

isolation

protecting soft tissues

margins limited to supragingival sulcus

Intra-coronal Cavity Preparation

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Principles of Cavity Preparation1. Outline form2. 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 lesions6. Finish margin of enamel walls7. Perform the toilet of the cavity

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 removedall faults includedmargins placed in position- good finishing of margins of restorationextension for preventionsufficient enamel & dentin to locate the pulpal & axial walls or prepn.surfaces within 0.5mm from DEJ

extent of carious lesion, defect/ faulty restorations

esthetic considerations

occlusal relationships

adjacent tooth structure

cavosurface margin

FACTORS

FEATURESpreserving cuspal strength

preserving marginal ridge strength

minimizing f-l extensions

enameloplasty

connecting to close faults

restricting depth

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Principles of Cavity Preparation1. Outline form

1. Cover all carious lesions2. No extension for prevention

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

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Principles of cavity preparation2. Resistance form

1. Depth- 0.5 mm below DEJ (about 1.5 mm from the deepest pit)

2. Flat floor3. No unsupported enamel (undermined)

1. Cavosurface margin: 90 degree2. Angle of departure: 90 degree

4. Slightly-rounded internal line angle5. Preserve marginal ridge if possible

PRINCIPLESutilize box shape with a flat floorrestrict extension of external wallsslight rounding of internal line angles - reduce stresscap weak cusps & envelope / include enough weakened toothprovide enough thickness of restorative material - prevent fracturemajor principle is that restoration should rest on flat sound tooth structure, perpendicular to occlusal forces directed parallel to the long axis of tooth

FEATURESrelatively flat floors box shape includes weakened tooth structurespreservation of cusps & marginal ridgesrounded internal line anglesadequative thickness of restorative materialsseats on sound dentin peripheral to excavation of infected dentinreduction of cusps for capping

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Flat FloorRelatively parallel to the cusp tips

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Cavosurface Margin

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

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Prepared Cavity Walls

1. Cavosurface margin 2. Enamel wall3. Dentinoenamel junction (DEJ)4. Dentin wall

Sharp definitecavosurface

margin

E

DEJ

DDefinite slightly-rounded internal line angle

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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 Preparation3. Retention form

Retention form : shape / form of prepared cavity that resists displacement / removal of restoration from tipping/ lifting forcesdefined 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

intra coronal-inside a cavity prepn,within the tooth

extra coronalon prepn.surface, replacing reduced ext.tooth

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Principles of cavity preparation3. Retention form

1. Box form2. Convergence to occlusal surface (small

undercut)3. Retentive groove4. Pins and slots5. Dovetail6. Acid etching (for resin composite restorations)

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Retention form

1. Box form 2. Convergence to occlusal surface (small undercut)

AB

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3. Retention FormDovetail

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Principles of cavity preparation3. Retention form

Retentive groove

Pins

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Retention Slot & Pin

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Principles of Cavity Preparation4. Convenience form

• Convenience form : shape/ form of cavity that provide adequate observation & accessibility

• ease of operation in preparing & restoring the cavity

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

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

caries left in pulpal / axial floor excavated

0.75-1mm of dentin cover the pulp

when affects esthetically

weakened tooth- given retention

secondary caries , if present

periphery of old resto.mate. not intact

PULP PROTECTIONpulpal injury, due to

heat generated while cuttingresto.mat.with good thermal conductivitychemicals from resto.mate.Galvanic currentsmicroleakage

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

SECONDARY RESISTANCE & RETENTION FORM

TWO TYPES

MECHANICAL FEATURES

CAVITY WALL CONDITIONING

� Mechanical featuresretention locksgrooves & covesskirtsbeveled enamel marginspins amalgapinsslots

Cavity wall conditioning featuresenamel, dentinal wall conditioningfor bonded restorations

FINISHING THE EXTERNAL WALLS OF CAVITY PREPARATION

further development when indicated, of a specific cavosurface design & degree of smoothness that produces maximum effectiveness of restorative material being usedto create best marginal seal bet.resto.mate.& toothto afford smooth marginal jnprovide 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.

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Concepts behind conservative restorations

1. Remove minimum tooth structure required for convenience form

2. Caries removal3. Access, carving and finishing margins4. Retention and resistance form

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False conservatism

1. Insufficient convenience form2. Leaving unsupported enamel3. Insufficient reduction for restoration

strength

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Advantages

1. Reduced risk of pulpal and perio involvement

2. Improved esthetics3. 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 fissures3. Rounded internal line angles to facilitate

condensation and minimize stresses4. Minimal pulpal depth is 0.5 mm into dentin from

DEJ5. No need to cross isthmus unless caries is

present.6. If questionable occlusal pits/fissures, consider

PRR or sealant