Introduction
Class I cavities are, in G. V. Black's classification, cavities that start in pits and fissures. This note covers the classical preparation of the simple occlusal Class I cavity in premolars and molars – designed for amalgam and the model from which every other cavity design is taught – and its two types, which differ in how far caries has spread along the fissure system. Pits and fissures are the most caries-prone surfaces of the dentition, so this is the preparation cut most often.
Class I cavities and the classical approach
Black's Class I covers caries in:
- the occlusal surfaces of premolars and molars;
- the buccal and lingual (palatal) pits of molars – most often buccal in mandibular and palatal in maxillary molars;
- the lingual pits of maxillary incisors, above the cingulum.
These blind pits are the foramen caecum (Latin: "blind opening"). Cavities that run from the occlusal surface onto the buccal or lingual surface, and foramen caecum cavities, belong to the next topic; this note deals with the purely occlusal cavity.
The classical (Black's) preparation was designed for amalgam, which does not bond to tooth and is brittle in thin section. The cavity must therefore hold the filling mechanically (retention form), let filling and tooth withstand chewing forces (resistance form) and give the material enough bulk. Black's principle of extension for prevention carried the outline along every deep fissure to areas considered self-cleansing. Today the outline includes only carious and deep, non-cleansable fissures; shallow ones are removed by enameloplasty or sealed.
The classical Class I cavity is a box: a flat pulpal floor just inside dentin, buccal and lingual walls parallel or converging occlusally, and margins on sound enamel supported by dentin.