This in vitro study assessed the influence of effect of surface roughness and auxiliary tooth preparation on the resistance form of complete metal crowns. Aluminium oxide particles of grit 50µ and 110µ were used to treat the intaglio surface and auxiliary features such as mesio- occluso- distal (MOD) slot and reduced occlusal convergence (ROC) were investigated. The frequently encountered problem in clinical practice is dislodgement of cast restorations. This displacement is mainly because the tooth preparation features do not oppose the forces led against the restorations. Therefore, the design of the tooth preparation is an important consideration in fixed dental prosthesis. Materials and Methods: 45 extracted maxillary premolar teeth were mounted on acrylic blocks. They were prepared to a standardised dimension of 3mm and taper of 15-20 degree.15 teeth had MOD slot and 15 teeth had ROC additional auxiliary feature. Cobalt chromium alloy metal crowns were casted. These samples were then segregated and were treated with aluminium oxide particles of 50 µ and 110 µ. The crowns were then cemented with glass ionomer cement and tested under universal testing machine at angle of 45 degrees to evaluate the resistance form. The force required to dislodge the crown was noted as resistance value. Results: There was significant difference in the resistance values when cobalt chromium metal crowns were treated with aluminium oxide particles and were incorporated with auxiliary feature. (p<0.001). Interpretation and Conclusion: Aluminium oxide particles and modified auxiliary features have an influence on the resistance form of complete metal crowns. Therefore, in cases with compromised crown height and taper ROC auxiliary feature should be incorporated and treated on the intaglio surface with 110µ aluminium oxide particles.
