Tadataka Sugimura

Measurements of Deformations of Teeth and Mandibles due to Occlusal Forces

When occlusal or masticatory forces were applied to teeth and mandibles, three dimensional (3-D) displacements of their deformations were measured quantitatively by double-exposure holographic interferometry. The mandibles were extracted from adult dogs. As measuring places, buccal surfaces of the teeth and mandibles were selected. When vertical load was applied to the first retromolar (M1), a tiltlike deformation was observed. By this the tooth was displaced to the buccal direction. Experimental observation of a sagittal section shows that deformations of the tooth are larger than that of the corresponding mandible. When a lateral load acted on M1, the buccal surface of M1 was displaced into the upper direction of the tooth axis from the dental socket. In these experiments, two kinds of tensile forces, 100 gm and 200 gm were applied to M1. When the buccal surface of the mandible in the neighbourhood of M1 was partly scraped, the same surface of the tooth was displaced further to the upper direction of the tooth axis. The mandible in the neighbourhood of M1 was displaced in the same direction. These results show that the periodontal membrane plays the role of a buffer and will be valuable to considerations of deformations of human teeth and periodontal diseases.

Holographic measurement on deformation of mandible with dental implants due to occlusion

To consider the dynamic response of implant bridge caused by occlusion, the deformation of the bridge and the near mandible subjected to occlusional force was measured by holographic interferometry. In the study, the mandibles of Japanese monkeys were used. A screw type ceramic implant was placed in the site of the second molar, when it was about one year since the mandibular first and second molars were extracted. An implant bridge was then fabricated and placed between the implant and the first and second premolars. After the mandibular bone was extracted, double exposure holographic interferograms were recorded under various loads for the mandible. It was found that the stress on the implant bridge concentrated on the mesial of the pontic when the vertical load was applied to the second premolar. This shows that the mandible near the implant receives most of stress and suffers frequent damage such as the bone resorption, when the loads were applied to its mesial side.

Holographic Investigation of Tooth Deformations

A bad approximal contact may cause food impactions between teeth by masticatory forces. This may give rise to caries or other paradental diseases. Many studies on approximal contact relation have been presented based on clinical experience [1] and considered from a morphological standpoint [2] up to now. However, there have been only few studies on approximal contact relation investigated from a functional viewpoint. Therefore, investigations of the deformations of teeth subjected to occlusial or masticatory forces and the mechanical effect to their adjacent teeth are very important. Deformations have been measured, until now, with mechanical instruments [3], [4] such as dial gauges and strain gauges. Recently, double-exposure holographic interferometry has been found useful to measure three-dimensional deformations of teeth [5], [6]. This method, however, is restricted to the measurement of deformations within a certain time interval. Real-time holographic interferometry, on the other hand, allows measuring such deformations continuously.