Three dimensional shape measurement of teeth by the system of laser displacement meter and computer controlled scanning machine. 2. The improvement of accuracy by means of the divisional measurement method.

Abstract

The accuracy of the three dimensional shape measurement of teeth was improved. The system was composed of a laser displacement meter and a computer controlled scanning machine. The compensation of errors which were observed when the reflected beam was shaded by the model teeth itself was attempted by connecting the data which were measured by rotating the model tooth at 180 degrees on the going stage. The accuracy of measurement was examined at the slope of 7 crown abutment tooth. When the model tooth were measured without tilting, the difference between the true value and the measured data was -240 microns (-2.8%). However, by tilting the model tooth at +/- 20 degrees on the going stage and connecting the two couples of data obtained, the difference considerably decreased into +/- 10 microns (+0.1%). In order to measure a complete crown abutment tooth with high accuracy and without error at the shaded portion, the model tooth was tilted +/- 30 degrees and rotated 180 degrees on the going stage and measured divisionally at four regions. The four partial data thus obtained were combined by using the software program. By the present procedure, the margin of the abutment tooth was recognized and the error data were eliminated. The overlapped data upon divisional measurements were excluded and the complete data of the single abutment tooth were saved into a file. They are possible to be the basic data for the future production of prostheses by means of CAM technique.