Source of Support: None, Conflict of Interest: None
This is-vitro study was conducted to find the importance of cavity designs in the fracture resistance of class II composite restorations in four different cavity designs. 32 freshly extracted teeth were used in the study. Group I received a mesio-occlusal preparation with extension through the occlusal groove into the central fossa. Group II received a mesio-occlusal slot preparation with retention grooves extending from the gingival floor to the occlusal surface at the axiofacial & axiolingual line angles. Group III received a mesio-occlusal slot preparation as in group II but without retentive grooves; Group IV received a mesio-occlusal slot preparation, without removal of facial or lingual portions of the mesial enamel shell. After the restorations were thermocycled, their marginal ridges were flattened & loaded to failure. Mean (SD) failure loads were 392.37(79.96) N in group I, 353.81(49.23)N in group II, 257.36(73.42)N in group III and 284.73(73.56)N in group IV. Mean failure loads of group I and II were not significantly different from each other but very significantly greater than failure loads of group III and IV. Mean failure loads of group III and IV were not significantly different.