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Cavity Preparation and Placement of Restoratives

Robert Wiggs United States

INTRODUCTION

Cavity preparation, in coordination with restorative material, and technique is the basis for successful restoration.

RESTORATIVE TERMS

 Enamel Prisms. Basic enamel unit running the dentinoenamel junction to the surface enamel.

 Undercut. A designed feature of a restorative preparation created by removing a portion of the dentin within the preparation for the intention of providing retentive qualities to a restoration.

 Overhang. An excess of restoration projecting beyond the parameters of a preparation margin resulting a projection or shoulder.

 Pin. A metal pin or wire cemented or threaded into the dentin at a preparation site to aid in retention of a restoration.

 Flashing. Restorative that extends beyond the preparation outline, but when initially placed does not cause an overhang.

G.V. BLACK MODIFIED CAVITY PREPARATION CLASSIFICATION SYSTEM

1.   I,PM,M; Beginning in structural defects, such as pit or fissure, commonly found on occlusal surfaces.

2.   PM,M; Proximal surfaces; when a tooth with a Class 2 lesion includes a Class 1, it is still considered a Class 2.

3.   I,C; Proximal surfaces, incisal angle not included.

4.   I,C; Proximal surfaces, incisal angle included.

5.   I,C,PM,M; Facial or lingual, gingival third; excluding pit or fissure lesions.

6.   I,C,PM,M; Defect of incisal edge or cusp; not included in Black's original classification.

Note: While this table shows a standard numerical system, Roman numbers may also be used (i.e., I, II, III, etc.) There may also be two separate lesions present on the same tooth (i.e., Class II, Class V) or a combination lesion where two locations are present and contiguous (i.e., Class II/V).

ELEMENTARY CAVITY CLASSIFICATION (CLASSIFICATION BY LOCATION)

 Simple. Involving only one tooth surface.

 Compound. Involving two tooth surfaces, when prepared.

 Complex. Involving three or more tooth surfaces, when pre­pared.

STAGING OF TOOTH INJURIES

These are generally referred to as stages, and used in combination with Black's Modified Clas­sification of Tooth lesion locations (Classification by extent of pathology).

Stage:

1.   Simple fracture of the enamel.

2.   Fracture extends into the dentin.

3.   Fracture extends into the pulp chamber; pulp vital.

4.   Fracture extends into the pulp chamber; pulp non-vital.

5.   Tooth displaced.

6.   Tooth avulsed.

7.   Root fracture; no coronal involvement; tooth stable.

8.   Root fracture; combined with stage 1-2 coronal fracture; tooth stable.

9.   Root fracture; combined with stage 3 coronal fracture; tooth stable.

10. Root fracture; in combination with stage 1-4; unstable tooth.

BASIC CONCEPTS OF RESTORATIVE PROCEDURES

When an injury or defect occurs in the dental tissues, it is generally best to preserve the function and structure of the tooth by restorative means. It is essential to know basic components of restorative efforts before undertak­ing therapy, including knowledge of cavity preparation, from skills involved to the final prep that is required.

RULES OF RESTORATION

1.   Conservation.

2.   Esthetics.

3.   Contours and contacts.

4.   Extension for prevention.

5.   Cavity Preparation.

6.   Identification and resolution of cause.

COMPONENTS OF PREPARED CAVITIES

Various walls, lines, and angles are created during cavity preparation. The following terms are used to identify the various components of a cavity prepared for restoration.

An enclosing side of a prepared cavity is termed a wall. The wall is named in relation to the tooth surface of which it is formed. There are two internal walls possible, the axial and pulpal walls. The axial wall is the internal wall formed by the surface of the long axis (axial or vertical plane) of the tooth. The pulpal wall is the internal wall in the horizontal plane.

PREPARATION OF CAVOSURFACE ANGLES OR MARGINAL FINISH LINES

Design of the cavosurface angle requires special considera­tion in its preparation. The preparation marginal restoration greatly affects retentive qualities of the restoration, resist­ance to marginal leakage, physiologic contour reactions, gingival health, and resistance to attrition, abrasion and fracture of the restoration and restored tooth. Selection of the specific cavo­surface angle treatment is dependent upon the type of restoration selected, restorative materials to be used, degree of anticipated stress demand upon the restoration, and the length and direction of the enamel prisms.

CAVITY PREPARATION

Multiple factors must be taken into consideration prior to the design of the preparation outline being implemented upon the tooth:

 Location.

 Extent.

 Stresses.

 Tooth condition.

 Esthetics considerations.

RESTORATIVE MATERIALS

Operative chairside restorations generally involve the use of one, or more, of three basic restorative materials; amalgam, glass ionomers, and composites. These products are held in place by macro-mechanical retention, micro-mechanical retention, or chemical crystal formations. Macro-me­chanical retention is undercuts in the dentin, and is used with non-bonded amalgams and self or auto cure composites. Micro-mechanical retention is obtained by the use of bonding agents that microscopically interlock in enamel porosities, dentinal tubules or other microscopic anatomy. This is used primarily with light cured composites, and bonded amalgam restorations. Chemical crystal formations occur with glass ionomers as they form a crystal between the ionomer and the minerals within the enamel and dentin.


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