Abstract: The apparatus comprises a first holder (10) fixed stationarily relative to the upper jaw to the patient's head, and a second holder (16) which is secured to the lower jaw. The second holder contains a number of distributed transmitters (S1, S2, S3) which successively supply stepwise ultrasonic pulses. A supplied ultrasonic pulse is successively received by all of the receivers (E1, E2, E3) of the other holder (10). By the transit times, the distances between the receivers and the activated transmitter may be noted. Changes of the sound velocity are detected by a reference path (S4R, E3; S3, E4R) and used for the correction of the transit time signals. By means of an additional, freely movable holder which also carries a number of transmitters and which contains a scanning tip, the position, data of individual teeth or of other points of the mouth may be imputted into the computer.