Dental casts are frequently used for measuring the size, shape and position of a tooth. We have developed an optical apparatus for measuring a three-dimensional profile of a dental cast. The measurement is based on the triangular method which detects a laser spot on a cast by an image sensor. The apparatus is computer-controlled and designed to achieve a total measuring depth of 40 mm, a data acquisition time of 25 ms per point and a minimum scanning pitch of 0.1 mm. The depth and lateral resolutions are 0.05 and 0.1 mm, respectively, within a depth range of 25 mm. As a particular application of the apparatus, three-dimensional movement of teeth, including rotational movement, during orthodontic treatment, has been quantified by means of the superimposition of tooth profiles using a computer.