Microstructural characterization of enamel at different walls of Class II cavities

Enamel microstructure critically determines its biomechanical behavior and adhesive interface quality. This study aimed to characterize the site-specific microstructure of enamel at different walls of a Class II cavity and to elucidate its potential influence on bonding and marginal integrity.

A standardized Class II cavity was prepared on the mesial surface of four human maxillary first premolars. Enamel from the gingival, buccal, lingual, and proximal walls (mesial) was sectioned, acid-etched, and examined using scanning electron microscopy (SEM).

The gingival wall exhibited a homogeneous structure of parallel-oriented prisms without Hunter-Schreger bands (HSBs). In contrast, the buccal, lingual, and proximal walls (mesial) showed a bilayered architecture: an outer layer of parallel prisms and an inner layer of decussating prisms forming distinct HSB patterns.

Based on the SEM observations, the gingival wall's uniformly parallel prismatic structure may contribute to its susceptibility to adhesive failure and marginal fracture, potentially explaining its clinical vulnerability to secondary caries. From a microstructural perspective, selective bevel preparation at the gingival wall may be hypothesized to improve bonding at this site, as it reorients the adhesion interface toward transversely cut prism ends, potentially enhancing mechanical retention and reducing enamel cohesive failure. Further studies are needed to test this hypothesis.