Measurement of the Margins of Partial-Coverage Tooth Preparations for CAD/CAM

Purpose: This study tested the hypothesis that a scanning laser 3-dimensional digitizer is a precise and accurate instrument to measure chamfered and beveled margins of partial-coverage tooth preparations for computer-aided design/computer-aided manufacturing (CAD/CAM). Materials and Methods: The margins were measured by the digitizer on stone dies and calculated by triangulation into a 3-D representation. Instrument precision was defined as the ability to reproduce the same margin in repeated measurements and expressed as the coefficient of variation as a percentage. Instrument accuracy for chamfered and beveled margins was estimated by correlating their measurements to the measurement of the margin of a spherical calibration 'phantom' with known dimensions. Accuracy was expressed as the standard deviation. Results: The precision errors for the box- and cusp-chamfered margins and cusp-beveled margins were 3.9%, 3.4%, and 2.4%, respectively. With regard to accuracy the standard deviations of the measurements of the box- and cusp-chamfered margins and cusp-beveled margins were 19 µm, 21 µm, and 24 µm, respectively, compared to 15 µm for the phantom. Conclusion: Measurements of chamfered and beveled margins by a scanning laser 3-D digitizer for CAD/CAM are (1) precise (error 4%) and (2) accurate, with a standard deviation of less than 9 µm compared to optimal measurements of the spherical margin of the phantom.