[Electric potential changes of newly cemented non-precious metal alloy crowns in the mouth].

In connection with edentulous prosthesis, it is significant to measure the thickness of the oral mucosa by a non-invasive technique in vivo. Ultrasonic waves of 15 MHz were used in an A-mode pulse reflection method. In order to check the suitability of the ultrasonic method, it was compared with the puncturing method on 10 sites of the maxillary mucosa in 6 dentated subjects.The results were as follows:1. The equipment has a small probe to measure the thickness of soft tissue in a limited oral cavity, and the axial resolution is 0.1 mm.2. The relationship between the mean values obtained by the ultrasonic and puncturing methods showed a high correlative coefficient of 0.94. Also, the standard error obtained from each subject by the ultrasonic method was smaller than that of the puncturing method.3. The difference in the thickness of the oral mucosa varied in individual cases, but compared with the same site of others, there was a regular tendency: the thinnest sites were in the center of the palate with a range of 1.3 to 1.6mm; the thickest sites were in the rear sides of the palate with a range of 5.5 to 5.9 rnm, the other sites were medium thickness.