PRINCIPLES AND

CONCEPTS OF CAVITY PREPARATION

• Chinthamani Laser Dental College

Introduction

CLASSIFICATION

BLACK’S CLASSIFICATION

Class I lesionLesions that begin in the structural defects

of teeth such as pits, fissures and defective grooves.

Locations include• Occlusal surface of molars and

premolars• Occlusal two-thirds of buccal and lingual

surfaces of molars• Lingual surface of anterior tooth

Class II Lesions

They are found on the proximal surfaces of the bicuspids and molars.

• Areas for class II decay involve:– Two-surface restoration of a posterior

tooth. – Three-surface restoration of a posterior

tooth. – Four- or more surface restoration of a

posterior tooth.

Class III lesions

Lesions found on the proximal surfaces of anterior teeth that do not involve or neccesitate the removal of the incisal angle.

Class IV lesions

Lesions found on the proximal surfaces of anterior teeth that involves the incisal angle.

Fig. 48-9 Class IV restoration.

Class V lesion

Lesions that are found on the gingival third of the facial and lingual surfaces of the anterior and posterior teeth.

Class VI

Lesions involving cuspal tips and incisal edges of teeth.

OTHER MODIFICATIONSCHARBENEU’S CLASSIFICATION

• Class II: Cavities on single proximal surface of bicuspids and molars.

• Class VI: Cavities on both mesial and distal proximal surfaces of posterior teeth that will share a common occlusal isthumus.

• Lingual surfaces of upper anterior teeth

• Any other usually located pit or fissure involved with decay.

STURDEVANT ’S CLASSIFICATION

CAVITY FEATURESimple cavity A cavity involving only one

tooth surface

Compound cavity A cavity involving two surfaces of a tooth

Complex cavity A cavity involves more than two surfaces of a tooth.

FINN’S MODIFICATION OF BLACK’S CAVITY PREPARATION FOR PRIMARY TEETH

• Class I: cavities involving the pits and fissures of the molar teeth and the buccal and lingual pits of all teeth.

• Class II: cavities involving proximal surface of molar teeth with access established from the occlusal surface.

• Class III: cavities involving proximal surfaces of anterior teeth which may or may not involve a labial or a lingual extention.

Class IV:• Cavities of the proximal surface of an

anterior tooth which involve the restoration of an incisal angle.

Class V • Cavities present on the cervical third

of all teeth of all teeth including proximal surface where the marginal ridge is not included in the cavity preparation.

BAUME’S CLASSIFICATION

• Pit and fissure cavities • Smooth surface cavities

CLASSIFICATION BY MOUNT AND HUME[1998]

• This new system defines the extent and complexity of a cavity and at the same time encourages a conservative approach to the preservation of natural tooth structure. This system is designed to utilize the healing capacity of enamel and dentin.

THE THREE SITES OF CARIOUS LESIONS

• SITE I:• Pits, fissures and enamel defects on

occlusal surfaces of posterior teeth or other smooth surfaces.

• Proximal enamel immidiately below areas in contact with adjacent teeth.

• The cervical one-third of the crown or following gingival recession, the exposed root

THE FOUR SIZES OF CARIOUS LESION

• Size 1–minimal involvement in dentin just beyond treatment by remineralisation alone

• Size 2-moderate involvement of dentin. Following cavity preparation, remaining enamel is sound well supported by dentin and not likely to fail under normal occlusal load. The remaining tooth structure is sufficiently strong to support the restoration.

• Size 3-the cavity is enlarged beyond

moderate .the remaining tooth structure is weakened to the extent that cusps or incisal edges are split or are likely to fail or left exposed to occlusal or incisal load. The cavity needs to be further enlarged so that the restoration can be designed to provide support and protection to the remaining tooth structure.

Size 4-extensive caries with bulk loss of tooth structure has already occurred.

PRINCIPLES OF CAVITY PREPARATION

Conventional concept [Black’s concept]

• Incisors and canine

• Molars and premolars

• Gingival third cavities

Principles of Cavity Preparation

Principles of Cavity Preparationcont’dFinal cavity preparation

Patient Preparation for Restorative Procedures

• Inform the patient of the procedure to be performed and what to expect during the treatment.

• Position the patient correctly for the dentist and the type of procedure.

• Explain each step as the procedure progresses.

RECENT CONCEPT

IATROGENIC FACTORS AFFECTING DENTAL PULP

CLASS I CAVITY

• Incipient lesion• #34 inverted cone bur is used to penetrate

the enamel and 0.5mm or less into the dentin

• Grooves and fissures is completed• Smoothen the walls and finish the cavity • Occlusal enamel walls will be approximately

parallel to the axis of the tooth • Pulpal wall flat and smooth.

Extensive area#2 or #4 round bur can be used to

enter and remove the decayBur should run at a slower speedLight feather touch to sweep out

deepest penetrations of decay.Smoothen the enamel walls and

finishing is done

• Final occlusal outline form will consist of sweeping curves and be devoid of sharp angles.

• Bevel on the enamel should not be placed at the cavosurface angle because of poor edge strength of amalgam.

CLASS II CAVITIES

PROXIMAL BOX-• The farther the gingival wall is carried down,

the deeper pulpally must be the axial wall to maintain the proper 1mm width .

GINGIVAL WALL-• Width should be approximately 1mmAXIAL WALL-• Smaller restoration flat• Larger restoration-curve to parallel the outside

contour

• CONVERGENCE-the proximal box line angles and walls should converge toward the occlusal approximately following the buccal and lingual surfaces of the tooth.

• 90 degree cavosurface angle shold be maintained.

• LINE ANGLES-the buccogingival and linguogingival line angles can be very slightly rounded.

• CAVOSURFACE-the buccal and lingual walls should be at right angles to the surface of the tooth and in the direction of enamel rods.

• CERVICAL ENAMEL RODS- at the cervical margin the rods incline slightly toward the occlusal.

• RETENTION-retention grooves may be placed into the buccoaxial and lingual-axial line angles ,but in a fashion which will not undermine the enamel walls.

• ISTHUMUS WIDTH-on the occlusal surface the isthumus width should rarely exceed the width of a channel cut.

• AXIOPULPAL LINE ANGLE-this can be rounded with a bur or hand instrument by sharp enamel hatchets.

PULPAL WALL-the pulpal wall may be flat or rounded slightly

and should be preparedso it is about 0.5mminto the dentin

OCCLUSAL WALL-the buccal and lingual walls of the occlusal step

may converge slightly as they approach the occlusal surface.

OCCLUSAL DOVETAIL- this should be extended to include the

susceptible or carious areas of each specific tooth. The outline form should be rounded,smooth,and graceful with a definite lock on the occlusal.

SPECIFIC MODIFICATIONS

• DEEP PROXIMAL CARIES

• SMALL FIRST MOLARS

• THIN CUSPS

DIFFERENCES IN CAVITY PREPARATION FOR PRIMARY

AND PERMANENT TEETH

PRIMARY TEETH PERMANENT TEETH

DEPTH OF THE CAVITY 0.5mm into dentin 0.2mm into dentin

OCCLUSAL TABLE Occlusal table is narrow as the buccolingual width of the tooth is less

Occlusal table is wider than the primary teeth

CONTACT POINT /POINT Because of the presence of contact area, buccal and lingual margins of the interproximal box must extend far enough towards the embrasure at the gingival margin to make them accessible for cleaning.

Because of the presence of contact area, buccal and lingual margins of the interproximal box don’t have to extend too far into the embrasure.

MARKED CERVICAL CONSTRICTION

Because of the marked cervical constriction the floor of the cavity can become too narrow if placed more gingivally

The cervical constriction is not that marked therefore sufficient width of the floor of interproximal box can be maintained.

ISTHUMUS OF THE CAVITY

Isthumus is narrow because the buccolingual width of the tooth is less.cavities with wide isthumus can lead to fracture of the tooth.

Isthumus is wider compared to primary teeth.

BEVEL IN CAVOSURFACE MARGIN OF GINGIVAL SEAT

Bevel is not given in the cavosurface margin of gingival seat

Bevel is given in the gingival seat

OCCLUSAL ASPECT OF THE PROXIMAL BOX

Must be kept narrow to prevent weakening of the cusp

Its not that narrow

GINGIVAL SEAT PLACEMENT

They are placed clear of contact with the adjacent tooth, so that the margins of the restorations can be cleaned.

It is not that wide.

BUCCAL AND LINGUAL WALLS OF THE PROXIMAL BOX

Because of the wider contact area the buccal and the lingual walls of the interproximal diverge buccally and lingually to clear the contact area.

Because of the prasence of contact point the buccal and the lingual walls of the interproximal need not be diverged towards the embrasure.

MOD CAVITY Should not be restored for amalgam alone.

It may be restored with amalgam.

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