Ichizoh Itoh

Morphological changes in the zygomatic arch during growth

Abstract Morphometry of the zygomatic arch was obtained using 30 Indian dried skulls at each of Hellmans dental stages: IIA, IIIA, IIIB, IVA, and VA, for a total of 150 skulls 300 sides. The following conclusions were obtained. 1.Though both the height and length of the zygomatic arch increased at all stages from IIA to VA, the rate of increase of the height indicated a value larger than the length. 2.The zygomaticotemporal suture consisted of the vertical element from the upper margin to the center and the horizontal element from the lower side to the margo inferior during the IIA period. This suture changed to a gradual curve from the upper margin to the margo inferior with the movement of the center and the lower side to the rear during the VA period. 3.The degree of interdigitation of the zygomaticotemporal suture increased from the IIA period to the IIIA and IIIB to IVA. These findings suggest that the form of the zygomatic arch and the zygomaticotemporal suture showed growth change adjusting to the functional change in mastication with growth.

Coronal Cementogenesis in Cattle Molar Teeth

Abstract Coronal cementum is generally noted in herbivorous animal teeth. Cementum is occasionally formed in the cervical area and the impacted tooth occlusal surface in humans. Therefore, it is suggested that coronal cementum is formed under certain conditions. In this study, using cattle premolar tooth germs, the relationship between the movement of cementoblasts and the initiation site of cementogenesis was observed, and the following results were obtained: 1. Cementogenesis was initiated in the bottom area of occlusal surface grooves, and gradually progressed toward the cuspal crest area. 2. When reduced enamel epithelial cells migrating from the enamel surface toward the dental sac were at a distance of 20–30 μm from the enamel surface, cementoblasts appeared and cementogenesis was initiated. These findings demonstrated that after the degeneration of reduced epithelium, coronal cementum was gradually formed, showing a relationship between the formation area and progression process of coronal cementum and tooth development, since the completion period for enamel formation differs between areas.

Relationship between the Cranial Morphology and Temporal Muscle in Insectivora, Suncus murinus

Abstract In observations of Suncus cranial specimens, tissue sections of the temporomandibular joint, and dissected sections of the temporomandibular joint articular surface and temporal muscle, the relationship between the temporal muscle and cranial morphology was evaluated. Morphology of the calvaria in the origin of the temporal muscle and that of the coronoid process in the insertion of the temporal muscle corresponded to marked development of the temporal muscle. The temporal muscle was composed of superior, middle, and inferior muscle bundles. The superior and inferior muscle bundles vertically overlapped the middle muscle bundles. Most of the muscle fibers were inserted in the thick fascia of the middle muscle bundle. The middle muscle bundle originated from the calvaria, ran in the horizontal outer anterior direction, and was inserted in the coroniod process. From the composition and course of the three muscle bundles of the temporal muscle, it was speculated that the main action of the temporal muscle was to pull the mandibular bone coronoid process in the horizontal inner posterior direction. This action of the temporal muscle influenced a series of bone morphology ranging from the inner surface of the coronoid process to the temporomandibular joint via the condylar process. From the articulatory direction of the superior and inferior joints of the temporomandibular joint, the size of the articular surface, and the presence of the articular disc, it was speculated that, in the temporomandibular joint, posterior-inferior inner action caused by the temporal muscle and articulation is received with the inferior joint as the fulcrum, in response to the mandibular supero-inferior movement caused by the condylar antero-posterior movement in the superior joint.