Distribution of Stress and Strain Produced in the Human Facial Skeleton by the Masticatory Force

Abstract

In an attempt to make analysis of stress and strain on the human facial skeleton due to chewing force, a series of experiments were carried out on dry skulls reproducing the mastication, Brief results are shown in Fig. 4 (ditribution of principal strains); Fig. 5 (distribution of strains along the free margins); Fig. 8 (distribution of strain normal to the supposed cross sections); and Fig. 10 (distribution of the maximum absolute values of the strains, i. e., relative strength of various parts), and they are summarized as follows :1) The strains in the facial skeleton increase generally as the load (Pd in Fig. 2 (A)) moves toward the foreteeth in consequence of the increase of the moment of the load about the mandibular joint.2) The direction of the axes of the principal strains changed according to the shift of the load along the dental arch. Nevertheless, the directions in the facial skeleton excluding the lower part of the maxilla and the forehead, are in some measure similar to the orientation of the split-lines.3) Intensive strains appear in the anterior region of the lower part of the maxilla. Fairly intensive strains appear in such region as the nasal root, medial end of the infraorbital margin, infero-lateral corner of the orbit and its inferior vicinity, and the orbital surface of the zygomatic process of the frontal bone.4) Strains in the facial skeleton show the remarkable occurrence of the bending moments.5) The mechanical behavior of the human facial skeleton seems to resemble that of the rigid frame structure.6) The infero-anterior part of the maxilla is relatively weak among various parts of the facial skeleton. This fact may suggest that the human facial skeleton is rather adapted to the use of the posterior teeth.The present study was carried out in the Department of Anthropology, Faculty of Science, University of Tokyo, before the author was transfered to the present institution. The author is deeply grateful to Professor Hisashi SuzuKI of the above department for his guidance and continuous suggestion during the course of the present study. The author also wishes to express his sincere thanks to Professor Teruyoshi UTOGUCHI, Assistant Professor Hiroyuki OKAMURA, and Mr. Shunsaku MITSUHASHI of the Department of Mechanical Engineering, Faculty of Technology, University of Tokyo for their instructive advice during the experiment of the present study.