Convergence Angles of Clinical Tooth Preparations Achieved by Dental Students at King Saud University, Saudi Arabia

The appropriate convergence angle (CA) for adequate retention and resistance of cast crowns has always been a matter of research and discussion. The purpose of this study was to measure the CA of tooth preparation for single crown (SC) or as abutments for fixed partial denture (FPD) carried out by final-year undergraduate dental students at the College of Dentistry, King Saud University and to compare them with the recommended CA. The convergence angles of 355 tooth preparations were evaluated and grouped into SC preparations and FPD abutment preparations. Dies were scanned using the computer-assisted design (CAD) system (Cercon, Degudent), and snapshots were then taken from buccal and mesial views. CA was calculated from a colored printout for each snapshot using a protractor. The overall mean CA was 18.56 degrees. Only 32.7 percent of the preparations were within the recommended CA (<12 degrees). The mean CA of SC (17.7 degrees) was less than the mean CA for FPD abutment preparations (19.58 degrees). The mean CA for anterior tooth preparations (15.8 degrees) was significantly less than the mean CA for posterior tooth preparations (20.3 degrees). The mean CA for mesio-distal axial wall preparations (16.66 degrees) was less than the mean CA for the buccolingual axial wall preparations (20.45 degrees). A wide range was found for the convergence of the axial walls among dental students. The recommended CA (<12) was difficult to achieve clinically by these students.