Hajime Hanamura

How Does the Pulpal Floor of a Molar Tooth Develop

Abstract Development of the pulpal floor was reviewed from both macroscopic and microscopic perspectives, and relations between individual variation in tooth roots and their development are considered. It has been thought that the pulpal floor of a molar tooth is formed as a continuation of the coronal dentine in rodents. In humans, the interradicular dentine develops from a separate mineralization center or centers (subpulpal lobe), and only later does it unite with the coronal dentine. The subpulpal lobe appears in the tooth germ of some mammals other than humans, but it is absent in mice. The molars of Suncus have a large pulpal floor, and are useful as a model of the development of the bifurcation area. The calcified process of the pulpal floor in Suncus is divided into two stages : (1) the primary subpulpal lobe appears, and (2) a secondary subpulpal lobe forms aggregated by the small calcified centers. The number of secondary subpulpal lobes determines the root number. The connecting line among the subpulpal lobes on the completed tooth becomes a ridge (interradicular crista) on the external surface, and a groove (isthmus) on the internal surface. The pattern of the interradicular crista seems to depend on the number of roots. We addressed the following three macroscopic variants and these developments ; (1) three-rooted mandibular molar, (2) enamel projection, and (3) gutter-shaped root. These structures relate to developmental events.

Numerical variation of teeth in the wild house musk shrew Suncus murinus captured from Nagasaki, Japan

Wild populations of Suncus murinus from Nagasaki were thought to be extinct, although specimens from Nagasaki are kept at the National Science Museum, Tokyo. Variation in the number of teeth, including both congenital and postnatal absence, was observed in 25 of 85 individuals. All 25 abnormal individuals were checked using a micro-CT unit to document the presence or absence of embedded teeth and any traits of postnatal absence. Four of these had congenitally absent teeth, whereas the rest showed signs of postnatal absence. There was no significant difference in the ratio of length of tooth group P(4)M(3) against palatal length between individuals with congenital absent teeth and normal ones. Because S. murinus in captivity shows a high rate of periodontal disease, we suggest that the high rate of postnatal absence of teeth in the wild population is due to oral diseases such as periodontal disease or other traumatic factors.

Observation of Lateral Mandibular Protuberance in Taiwan macaque (Macaca cyclopis) Using Computed Tomography Imaging

Morphological characteristics of the protuberance on the external surface of the mandible in Taiwan macaque (Macaca cyclopis) was investigated using cone-beam computed tomography. We observed 49 skulls of M. cyclopis. Of 7 skulls with deciduous and mixed dentitions in which M2s did not erupt, the protuberance was not found. Of the 13 skulls with mixed and permanent dentitions in which M2s had erupted, a palpable protuberance was found in one specimen. Of the 29 samples in which M3s had erupted completely, a perceptible protuberance was found in 2 samples, and palpable protuberance was found in 8 samples. Thus, the protuberance was found in 10 samples of the 29 samples with complete dentitions (34.5%), and the emergence of the protuberance may have been related to mandibular growth. In the case of the well-developed protuberance, it extended from the P4 to M3 region but did not extend to the mental foramina. By using cone-beam computed tomography, it was determined that the protuberance was composed of cortical bone and was the thickest in M2 region. Since the protuberance consisted of homogeneous cortical bone, it was considered to be the result of normal bone growth similar to the mandibular torus in humans.