[Three dimensional shape measurement of teeth. (5) On the measurement by the newly developed double sensor laser displacement meter].

A laser displacement meter equipped with two PSD (Position Sensitive Device) sensors located 45 symmetrical to the incident beam was developed to measure the three dimensional shape of a tooth with a higher efficiency and accuracy. This displacement meter enabled compensation of the data at the shaded points without the rotational measurement which could not be done by the former single sensor displacement meter. The output voltages on the declined plane measured by the two sensors were different on the complicatedly declined plane. in such a case, the output measured by the sensor which made a larger angle with the declined plane was adopted since it was affected less by the secondary scattering. All regions of the 6 molar were measured without errors, and the cusps and fissures of the occlusal plane were measured as precisely as by the single sensor displacement meter. The time required for the measurement was about 10 min, which was one third that required for the former single sensor displacement meter. For measurement of a crown abutment tooth with steeply inclined slope and margin, by the single sensor displacement meter, the tooth area had to divided into four parts by tilting and rotation on the gonio stage, and required about one and half hours. However, with the present displacement meter, only the measurements with tilting were required and the time was reduced to about 40 min. Besides, the data connection for CG was accomplished in about 5 min, and the complete data without errors and overlap could be saved. This data will be able to give the inner shape of a crown for machining by CAM technique. As mentioned, the newly developed double sensor laser displacement meter greatly simplified the procedure to measure the shape of a tooth and enabled measurements with high precision.