General.

Cavity preparation is largely a mechanical procedure in which hand excavating instruments and motor driven burs, disks, and stones are used to remove caries and debris and to cut and shape tooth structure. Speeds used with rotating cutting instruments vary from the range of 4, 000 to 10, 000 revolutions per minute (rpm) to " high" speeds of 500, 000 rpm or more. Instruments and techniques vary with the speeds, and the dental assistant should be familiar with these differences and be prepared to adapt readily to assist in the use of any technique.

Instrument and Material Setup.

Specific instruments used in cavity preparation will be determined by the dentist's preference and by the location of the cavity and the type of restorative material to be used. Instruments and materials used in preparing the cavity for an amalgam restoration include the contra-angle hand piece and appropriate hand instruments and burs, stones, and disks.

Procedure

Resistance form, retention form, and convenience form. The dentist will begin each procedure by selecting one of the burs we have discussed, and then outlining the cavity preparation. This establishes the general outline that the preparation will take, or how it will appear on the surface of a tooth. The bur used to accomplish this procedure will depend on the dentist's preference. The burs that might be used are the inverted cone, straight fissure, or tapered fissure burs. After outlining the cavity preparation, the dentist will want to obtain the resistance and retention forms. Though resistance and retention are not the same, both are accomplished at the same time. Resistance form is a form whereby the tooth and the restoration are able to resist the normal forces of mastication regardless of loss of tooth structure caused by caries and cavity preparation. Retention form is a form that tends to prevent dislodgment of the restoration and is characterized by lock, dovetails, and undercuts. This step may also be accomplished with burs: a small round bur, inverted cone, or tapered fissure bur. Convenience form will be accomplished at this time to obtain access for removing the remaining decay and to facilitate placement of the restorative material.

High speed procedures.

Use of high speed cutting instruments reduces cutting time, increases operator control of the instrument (no tendency to bind, wedge, or hop), and lessens patient apprehension and operator strain and fatigue.