[Studies on stress distribution under simulated muscles on dry skull]

In case of occlusion, the mandible is elevated by the muscles of mastication with T. M. J. as the fulcrum point, and at this time, the masticatory force concentrated mainly on the dental arch is absorbed into the jaw bone through the periodontal tissues. Therefore, it is of great significance for the study of prosthodontics to assess what distribution of mechanical strain the maxillar and mandibular bones exhibit to occlusal force at mastication. Very many studies have been made to clarify this point, but many of them were analyses of stress pattern when a tooth (a point) is under force on models prepared on the assumption that a tooth is planted on the jaw bone, but there are only very few studies which made analysis of stress pattern when the mandible is under force by elevating it mainly along the direction of the M. masseter upon positioning the bone similarly as in vivo mechanism. With the purpose of assessing the distribution of mechanical strain received when the mandible is elevated by the muscle of mastication, the author has assessed the change in the stress distribution under 2 conditions of light and hard tensile forces by setting the M. masseter form the center of the inferior border of the zygomatic bone and center of the zygomatic arch to the mandibular angles on the assumption that self memory alloy takes the places of the M. masseter (the masseter) and M. temporalis (the temporalis) on the experimental model. As a result, the following conclusions have been reached: 1. When the origin of the masseter is at the center of the inferior border of the zygomatic bone, the maximum exhibited tensile strain at all the measuring points both under light and hard tensile forces. Under light tensile force, the minimum strain showed compressive strain in the region from the lower canine to the lower first under hard tensile force, the minimum strain exhibited tensile strain at all measuring points. The amount of strain under hard tensile force exceeded the amount under light tensile force. 2. When the origin of the masseter is at the center of the zygomatic arch, the maximum strain showed tensile strain at all the measuring points both under light and hard tensile foece. The minimum strain exhibited compressive strain at all the measuring points both under light and hard tensile foece. The amount of strain under hard tensile force always exceeded the amount under light tensile force.(ABSTRACT TRUNCATED AT 400 WORDS)