ABSTRACT
Background: Many diseases and conditions weaken the strength of tooth making it to fracture. Many cavity designsand materials are used to restore the tooth to bring about the normal function. The present study was done to determine which one of the three class II cavity design offer the best fracture resistance to the teeth when used with different restorative materials. Methods: 165 molars (150 intact and 15 carious) were collected and preserved in hydrogen peroxide. These teeth were divided into five groups and restored with silver amalgam, compomer (Dyract AP) and metal modified ionomer cement (Miracle mix). The restored teeth were subjected to a compressive load using Universal Testing Machine by flat and metallic die. Results: Conventional designs with amalgam restoration seemed to withstand more load when it was imparted through a flat surface (741 kg ±158 SD) compared to the box or slot designs. However, when the load was imparted through a metallic die, the slot design with compomer restoration gave the maximum value (SD) of 472 (±88) kg. When analyzed statistically on the difference in the fracture resistance among the different restoration materials and the different cavity designs, statistically significant values were found between certain combinations. Conclusion: The study concluded that in the case of silver amalgam material, the test conducted by flat surface gives the best strength for the conventional design which is 3% and 23% better than that of box type and slot type respectively. However, when tested with a metallic die, slot type takes 8.3% more load than the conventional type. Among the various restoration materials tested for, amalgam provides more strength followed by compomer and miracle mix.