[Three dimensional shape measurement of teeth (4). On the measurement by the laser displacement meter which is able to move on Z-direction].

A three dimensional shape measurement using a wide area teeth model was constructed using a high precision laser displacement meter, teeth model scanning machine and personal computer. The system employed a Z-directional movement of a laser displacement meter which tracked wide and complicated changes of shape, allowing for the accurate measurement of not only the crown and alveolar crista of the molar, but also maxillary root, the height difference between which extends about 25mm. As for the labialis of the incisors, teeth model was stood on a gonio stage and measured. In the present study, arrange arc and rugged array of incisors were measured. Improvements in the accuracy of measurement were also expected. Higher resolutions were obtained by the measurement at the center of the measurable range of the displacement meter where the laser beam is most focused. Since the lineality of the measured value varies with the sensitivity coefficient, if the coefficient drifted, values measured in the outer measurable ranges yielded large errors than those in the central positions. The present Z-directional movement enables measurement at the center of the measurable range, yielding smaller errors. The data obtained with the present method of Z-directional movement of a laser displacement meter enables not only the precise measurement of the shape and position of teeth for CAD prosthesis design but also provides basic data for simulation of occlusion by adding the relative positions of the maxilla and mandible to computer models.