RESUMO
PURPOSE: To evaluate the fracture resistance of teeth restored with direct and indirect restorations of composite resin and restored with indirect ceramic restorations. MATERIAL AND METHODS: Fifty-six maxillary premolar teeth were chosen and divided at random into seven equal groups; Group 1 (control): intact teeth; Group 2: MOD cavity preparations, 1/2 intercuspal distance, with rounded internal angles, convergent walls, unrestored; Group 3: MOD cavity preparations, 1/2 intercuspal distance, divergent walls; Group 4: same preparation as Group 2, restored with direct composite resin (Single Bond/Filtek Z250-3M); Group 5: same as Group 3, restored with indirect composite resin (Artglass/Single Bond/Rely X); Group 6: same as Group 3, restored with indirect composite resin (Targis/Single Bond/Rely X); Group 7: same as Group 3, restored with indirect ceramic restoration (Empress/Single Bond/Rely X). The specimens were subjected to a compressive axial loading in a Universal testing machine at 0.5 mm/minute by means of a steel bar (8 mm in diameter). RESULTS: The mean fracture strength obtained was: Group 1: 1.91 kN; Group 2: 1.06 kN; Group 3: 0.93 kN; Group 4: 1.45 kN; Group 5: 1.81 kN; Group 6: 1.81 kN; Group 7: 1.77 kN. The restored teeth with direct composite restoration increased the fracture resistance of Group 4 up to 76% of a level comparable with the intact teeth (Group 1). However, statistical analysis indicated no significant (P < 0.05) differences between Group 1 (intact teeth) and restored teeth groups, with direct restorations as well as indirect restorations. Both cavity preparation designs weakened the remaining tooth structure. These results demonstrated that a bonded indirect restoration could satisfactorily be an ideal option for restoring teeth weakened by wide cavity preparation.