The ability of dental students and faculty to estimate the total occlusal convergence of prepared teeth

Statement of problem: Total occlusal convergence (TOC) is an important aspect of tooth preparation, but the accuracy of its visual estimation has not been determined. Purpose: The purpose of this study was to determine which TOC angles are considered ideal, maximal, and minimal, and also to determine the accuracy of visually estimating TOC. Material and methods: Thirteen dentoform teeth were prepared, for complete gold crown restorations, with TOC angles ranging between -3 and 30. Thirty students and 30 faculty members visually identified the teeth they believed had ideal, maximal, and minimal convergence and then estimated the angle of TOC for each tooth. Data were analyzed with a 2-sample binomial test and the 2-sample t test (α=.05), as well as the general linear model (the mixed procedure). Results: Teeth selected had TOC angles of 9-12 degrees, 21-30 degrees, and 3-12 degrees for ideal, maximal acceptability, and minimal acceptability, respectively. Students and faculty exhibited similar visual estimation capabilities. Greater accuracy of visual estimation of TOC angles occurred with teeth judged to have minimal or ideal convergence, as opposed to those with maximally acceptable angles, indicating estimation accuracy decreased as convergence increased. More than half of the estimates were within 5 degrees of the measured TOC. However, 11 ideal, 14 maximal, and 5 minimal estimates were judged inaccurately by 11 to 20 degrees, and 5 estimates were inaccurate by more than 20 degrees. There were more underestimates than overestimates. Conclusions: Most visual estimates were accurate, but several were inaccurate by more than 10 degrees. The most common inaccuracies were underestimated TOC. Students and faculty were not significantly different in their ability to accurately estimate TOC. Students and faculty were less accurate when estimating large, as opposed to small, TOC angles. (J Prosthet Dent 2009;101:7-12).