Objectives: The purpose of this study was to compare the actual CA values of tooth preparations to those visually estimated by experienced prosthodontists, and to compare performance between prosthodontists. Materials and methods: Three prosthodontists visually estimated the mesiodistal and buccolingual convergence angles (MDCA and BLCA, respectively) of 65 randomly selected premolar preparations made by dental students on typodonts. Preparations were scanned in three dimensions and digitized.

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... ctual MDCA and BLCA values were measured by three-dimensional imaging software. Data were analyzed by Friedman test (α=.05) and pairwise multiple comparisons with the Bonferroni adjustment (α=.0042). Results: The mean actual MDCA was 10.66 ± 3.96 degrees, compared to visual estimates of 13.86 ± 12.01, 21.94 ± 6.11, and 12.49 ± 8.38 degrees. The mean actual BLCA was 11.31 ± 4.80 degrees, compared to visual estimates of 13.32 ± 10.93, 23.52 ± 6.18, and 8.83 ± 5.75 degrees. The Friedman test resulted in χ 2 (3) = 68.54 (P<. 05) for MDCA and χ 2 (3) = 100.07 (P<.05) for BLCA. Multiple comparisons indicated that two prosthodontists provided CA estimates that were similar to each other (MDCA, P=1.0; BLCA, P=.042) and to the actual CA values (MDCA, P=.804 and P=.457; BLCA, P=1.0 and P=.006), whereas one prosthodontists provided higher CA estimates compared to the actual CA values and the other prosthodontists (P<.0042). Conclusions: One out of three of prosthodontists gave high CA estimates of tooth preparations compared to the actual CA and other prosthodontists' estimates.