[Three dimensional shape measurement of teeth (3). The divisional measurement method of abutment teeth]

In order to improve the accuracy of the three dimensional shape measurement, the divisional measurement method, which tilts and rotates the abutment teeth was attempted. This system is composed of a high precision laser displacement meter, teeth model scanning machine and personal computer. For the measurement of a crown abutment tooth with indistinct margin lines, the measuring area was divided into four regions of the mesio-distal sides and the buccal-lingual sides. The tooth was tilted on the gonio stage +/- 30 degrees around the mesio and distal direction, rotated 180 degrees around the tooth axis, and measured divisionally. The partial data thus obtained were combined by means of the software program into the composed data. Using this method of measurement, the margin of the abutment tooth was recognizable, and the faulted data, which arose from shielding of the receiving beam, was eliminated. Overlapping data from divisional measurements were deducted and the complete data for the single abutment tooth was saved into a file. In the case of a MOD inlay abutment tooth, the divisional measurements with only rotation were carried out, since each curved wall makes nearly a square angle and sharp boundary. A couple of data sets were combined and complete data without error was obtained. Thus, measurements of abutment teeth were obtained without error. It is possible to get the basic data for the production of crown and inlay by means of CAM technique.