Measurement of the margins of partial-coverage tooth preparations for CAD/CAM

Purpose: This study tested the hypothesis that a scanning laser 3-dimension al digitizer is a precise and accurate instrument to measure chamfered and beveled margins of partial-coverage tooth preparations for computer-aided d esign/computer-aided manufacturing (CAD/CAM). Materials and Methods: The ma rgins were measured by the digitizer on stone dies and calculated by triang ulation 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 c hamfered and beveled margins was estimated by correlating their measurement s to the measurement of the margin of a spherical calibration "phantom" wit h known dimensions. Accuracy was expressed as the standard deviation. Resul ts: The precision errors for the box- and cusp-chamfered margins and cusp-b eveled margins were 3.9%, 3.4%, and 2.4%, respectively. With regard to accu racy the standard deviations of the measurements of the box- and cusp-chamf ered margins and cusp-beveled margins were 19 mu m, 21 mu m, and 24 mu m, r espectively, compared to 75 mu m 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 deviatio n of less than 9 mu m compared to optimal measurements of the spherical mar gin of the phantom.