Cavity preparation can be defined as the procedure by which caries are removed and the area of the tooth is shaped to retain the restoration.
PRINCIPLES OF CAVITY PREPARATION
The traditional Cavity preparation is composed of seven essential steps. In the first three steps, the dentist examines the tooth that needs the cavity preparation.
1. Outline form. The curved shape and border of the tooth and restoration; also includes extension for prevention.
2. Resistance form. The form and the thickness given to the tooth and restoration to prevent displacement or fracture of either.
3. Retention form. The relationship of the tooth walls to prevent displacement of the restoration.
4. Convenience form. The procedures by which the operator gains access to the cavity preparation and by which instruments can fit into the cavity preparation to place restorative materials.
5. Removal of caries. The procedure of removing decayed tooth structure, followed by placement of the bases or liners.
6. Finishing of enamel walls. The process of angling, beveling, or smoothing of the preparation’s walls with appropriate instruments (e.g., hatchets, hoes, margin trimmers).
7. Cavity debridgement. Removal of debris and the cleansing of the cavity preparation to assure a clean, dry surface for the restorative placement.
Cavity Walls, Angles, and Bevels Cavity Walls
The sides of the cavity preparation are named to correspond to the surface of the tooth toward which it’s placed. For example, the pulpal wall would be at the base of the preparation near the pulp of the tooth, the lingual wall would be toward the tongue, the buccal wall would be toward the cheek, and so forth. The buccal wall (nearest the cheeks for posterior teeth) and the labial wall (nearest the lips for anterior teeth) are known also as the facial wall (for either posterior or anterior teeth).
The angle that is formed at the junction of two walls of a cavity preparation is called the line angle. Its name is created by compounding the names of the two surfaces involved. For example, the angle formed by the mesial and facial walls of a preparation is called mesiofacial, This format follows for all the possible line angle names. The junction of the cavity wall and the external surface of the tooth is called a cavo-surface line angle.
The junction of three cavity preparation walls forming a corner of the preparation is called a point angle. As with line angles, compounding the names of the three associated tooth surface walls forms the name. An example of a point angle is the disto-bucco-pulpal angle.
Tooth preparations with an angle to the cavity wall are called bevels. Traditional amalgam preparations use proximal wall bevels to retain the metal restorations. Modem adhesive restorative preparations utilize beveled surface margins to blend the restorative to the tooth surface and provide more tooth to be bonded to, making the restorative virtually undetectable.
Cavity Preparation Types
Cavity preparation are named for the tooth surfaces involved. Compound names are created as for line angles.
For example, a common three-surface posterior restoration involving the mesial, distal, and occlusal tooth surfaces is designated MOD and spelled mesio-occluso-distal.
Classification of Cavities
- There are five classifications of cavity preparation according to Blacks description.
- Class I cavities are pit and fissure decay that involve the occlusal, buccal, or lingual surfaces of a posterior tooth. Class I cavity may also be on lingual surfaces of maxillary incisors.
- Class II cavities involve the proximal surface of posterior teeth, such as the mesial and distal surfaces. In the cavity design, the occlusal is usually included.
- Class III cavities are found on the proximal surfaces of anterior teeth but do not involve the incisal edge. In the cavity design, the lingual or facial surfaces are usually included.
- Class IV cavities are found on the proximal surfaces of anterior teeth that involve the incisal edge.
- Class V cavities are found on the gingival third of the labial, buccal, or lingual surfaces of any tooth. This can include root erosion/abrasion.
A sixth classification of cavities, Class VI, was added to Black’s classifications. These Cavity preparation involve the incisal edge of anterior teeth and/or the cuspid portion of posterior teeth.