Fracture strength and fracture patterns of maxillary premolars with approximal slot cavities

The fracture strength and fracture patterns of maxillary premolar teeth prepared with two different cavity designs and tested with and without amalgam restorations were determined. No significant difference in the fracture strength of intact premolars and premolars prepared with conventional MOD cavities or slot MO/DO cavities was found whether or not the teeth were restored with amalgam. However, fracture pattern analysis revealed significant differences among the groups of teeth. Premolars with MO/DO slot cavities or slot amalgam restorations exhibited minimal fractures that involved enamel only in the majority of the cases. This behavior was similar to what was observed with intact premolars. In contrast, premolars with conventional MOD cavities or MOD amalgam restorations exhibited severe fractures that involved enamel, dentin, and the root in the majority of the cases. These severe fractures were statistically significantly different from those of premolars with slot cavities or slot restorations as well as from those of intact premolars. It is concluded that when maxillary premolars require restoration of carious lesions on both approximal sides without occlusal involvement, MO/DO slot amalgam restorations will be expected to result in teeth that are unlikely to undergo severe cuspal fracture compared to conventional MOD amalgam restorations.