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Steps for Cavity Preparation

Preparations are the first step in restoring a tooth that either has a carious lesion or has been fractured or otherwise physically damaged. Preparations are based on outline, retention, and resistance forms after decayed tissue has been removed.

The outline form and prep are created using carbide or diamond burs with a high-speed handpiece. A slow-speed handpiece with a steel bur and hand instruments typically are used to remove decayed dentin and finish the preparation.

For example, the technique would be to employ a pear-shaped bur in a high-speed handpiece to a depth of less than 2 mm in a Class I carious lesion involving all of the occlusal fissures on a molar tooth. The doctor can use a spoon excavator to remove any remaining decayed dentin by stopping at 2 mm.

The pear-shaped bur creates a subtle convergence toward the occlusal opening. This creates an “undercut” effect or the retention form, which will help keep the restoration in place.

A large round bur in a slow-speed handpiece can be used to remove decayed dentin from the subfloor of the preparation while slow-speed burs can be used to finish the walls and floor of the cavity.

If a carious occlusal lesion in a molar is connected to another lesion on the buccal or lingual surface, it will be necessary to perform a Class I cavity preparation with a buccal or lingual extension. If the second lesion is below the level of the pulpal floor, the preparation for the extension may need to include a “step”.

A freestanding lesion may occur on the buccal or lingual side of a molar, or on the lingual side of incisors. Typically, the outline form for this preparation is a little larger than the lesion. The preparation is round, oval, or triangular.

A convenience form used for access to a two-surface cavity preparation results in a proximal box preparation. The retention form is created when the floor is larger than the occlusal opening. The proximal part of the restoration can be kept from moving horizontally by carefully creating retention grooves.

In order to further protect the stability of the remaining tooth structure in maxillary molars and lower the risk of fracture, the dentist might need to remove areas of unsupported enamel by beveling the gingival cavosurface

The best way to provide long-lasting restorations is to use proper cavity preparation techniques and select the right design. It is important to use sharp and new burs for these procedures as well as proper isolation and moisture control. When restoring with composites, moisture control, polymerization shrinkage, and light curing also impact the success and longevity of a restoration.