Aim: The resistance and retention forms as the determining factors affecting the success of retention of resin-bonded restorations. The present study was conducted to compare the effects of diamond rotary burs with different grit sizes on retention of resin-bonded restorations. Materials & Methods: 80 maxillary central incisors was removed and polished surfaces of the teeth were prepared with four groups of rotary diamond burs with super-coarse, coarse, medium, and fine grit sizes. 80 restorations were casted with nickel-chromium alloy and bonded with Panavia cement. The samples were mounted on a universal testing machine and an axial load was applied along the cement-restoration interface at the crosshead speed of 0.5 mm/min to assess the shear bond strength. Results: Statistical analysis and interpretations were quite interesting and revealed that the differences was non- significant (P> 0.05). Group I, group II and group IV showed 15% and group III showed 10% of type I debonding. Most commonly type II debonding was seen and it was 75% in group IV, 70% in group III, 60% in group II and 50% in group I. Type III debonding was seen 35% in group I, 25% in group II, 20% in group III and 10% in group IV. Conclusion: The shear bond strength in samples prepared by super course diamond burs were significantly higher than course, medium and fine burs. The success of retention of resin-bonded restorations depends on retention, resistance and roughness of abutment teeth. Clinical significance: With the advent of resin bonded restoration, the replacement of missing teeth has become easy and effective management may be done in the benefit of the patient. However, for the success of resin bonded restoration, factors such as retention form, resistance for, grit size, surface roughness plays important role. Thus by this study, factors affecting failures can be determined.
Key words: Nickel-chromium, Resin bonded restoration, Shear strength.