Three dimensional shape measurement of teeth. (3) The measurement by the newly developed laser displacement meter with double sensors.

A laser displacement meter which equips two sensors was developed in order to measure the shape of teeth with higher efficiency and accuracy. By this displacement meter the rotational measurement to compensate the data at the shaded points became needless. The measurement of the 6 molar was carried out, and the regions such as cusps and fissures of the occlusal plane were measured precisely without errors. The time required for the measurement was about 10 min. and reduced to one third that of the previous system. While, by the measurement from one direction, the undercut portion such as toothneck is less accurate. Then, 7 molar model was tilted on the gonio stage with +/- 20 degrees and measured divisionally, and two groups of data were connected. By this method, the whole shape of tooth including the undercut portion became to be measurable. In the case of a crown abutment tooth with steeply inclined axial wall and margin, tilting method was also applied to measure more accurately. 7 abutment was tilted with +/- 30 degrees and measured and connected. The gingival and marginal line which are the characteristic spots for designing the crown were recognized. These data thus obtained will be able to give the inner and outer shape of crown for processing the prostheses by CAD/CAM technique.