2022 Volume 42 Issue 2 Pages 194-205
[Introduction] The human maxillofacial morphology has gradually changed from ancient times to the present, and the greatest change is considered to be progressive reduction of the jaw bone size associated with decreases in masticatory force due to softening of the diet. It is a well-known that bone adapts to mechanical conditions and changes its morphology, but the association between masticatory force, especially dentition and number of teeth, and maxillofacial morphology has not been biomechanically established. In this study, we prepared three models of the maxillofacial skeleton and considered the causal relationship between mastication and morphological change in the jaw bone from the viewpoint of mechanical responses to changes in the dentition and number of teeth with a review of the literature. [Materials and Methods] To clarify mechanical behavior of the maxillofacial skeleton associated with changes in dentition, a normal occlusion model (analysis model 1), bilateral mandibular first molar defect model (analysis model 2), and bilateral first and second molar defect model (analysis model 3) were prepared from CT image data of actual patients, and analysis was performed using finite element analysis software (MECHANICAL FAINDER version 11.0, Research Center of Computational Mechanics, Inc., Tokyo, Japan). [Results] ① In normal occlusion, stress was distributed widely on the front surface of the maxillofacial skeleton, and occlusal force was transmitted to the upper and lower jaw bones and anterior parts of the facial cranium via the teeth. Also, dense convergence of horizontal components was observed near the midpoint between the bilateral orbits, which was in agreement with the anatomical reinforcement structure of the facial cranium. ② With loss of teeth, the burden on the remaining teeth, particularly the most distal molars, increased, stress in the anterior aspect of the maxillofacial skeleton centering around the nasal cavity and midpoint between the bilateral orbits and mandibular condyles increased relative to the areas immediately above the tooth defects, and the burden of the surrounding bone tissues including the temporomandibular joints increased with decreases of support in the molar region.
