Comparison between digital superimposition and microcomputed tomography methods of fit assessment of removable partial denture frameworks

Statement of problem. The fit of removable partial denture frameworks should be assessed to optimize clinical adaptation. Potential discrepancies between framework and supporting structures are typically precisely measured with negative subtracts and high-resolution equipment. The growth of computer-aided engineering technology allows the development of new methods for the direct evaluation of discrepancies. However, how the methods compare is unclear. Purpose. The purpose of this in vitro study was to compare 2 digital methods of fit assessment based on direct digital superimposition and microcomputed tomography indirect analysis. Material and methods. Twelve cobalt-chromium removable partial denture frameworks were fabricated by conventional lost-wax casting or additive manufacturing techniques. The thickness of the gap between occlusal rests and respective definitive cast rest seats (n=34) was evaluated by using 2 different digital methods. Silicone elastomer impressions of the gaps were obtained, and microcomputed tomography measurements were used as controls for validation purposes. Digitization of the framework, the respective definitive cast, and the combination was followed by digital superimposition and direct measurements with the Geomagic Control X software program. Because normality and homogeneity of variance were not verified (Shapiro-Wilk and Levene tests, P<.05), the data were analyzed with Wilcoxon signed rank and Spearman correlation tests (a=.05). Results. The thicknesses measured by microcomputed tomography (median=242 mm) and digital superimposition (median=236 mm) did not reveal statistically significant differences (P=.180). A positive correlation (r=0.612) was detected between the 2 methods of assessing fit. Conclusions. The frameworks presented median gap thicknesses under the limit of clinical acceptability without differences between the proposed methods. The digital superimposition method was determined to be as acceptable as the high-resolution microcomputed tomography method for assessing removable partial denture framework fit.