The class system in place during the Edo (early modern) period in Japan is thought to have included a range of customs that differed between the samurai (ruling class) and commoners. The incidence of caries in the dentition of the samurai was significantly lower than that of commoners. This difference is considered to be due to diet, eating frequency, and tooth care. As to location of the caries, it was found that the incidence of root caries in the samurai was remarkably lower than that in commoners. Root caries does not occur until gingival attachment recedes in an apical direction. The samurai and commoners did not show a significant difference in incidence of periodontal disease, while many samurai dentitions exhibited slick-polished teeth and wedge-shaped defects, which are thought to have been caused by the customary brushing of teeth. Such a custom might have successfully prevented dental caries. Given these findings, we consider that the lower incidence of caries in the samurai, compared with commoners, resulted from the influence of oral hygiene practices that helped to prevent root caries.

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The strict class system in place during the Edo (early modern) period in Japan is thought to have encompassed customs that differed between the samurai (ruling class) and commoners. This study found that in samurai children, deciduous caries occurred only in maxillary incisors at 0.5-2 years of age and did not occur in the mandibular incisors and canines at 3-5 years of age. Conversely, in commoner children, deciduous caries occurred in all maxillary teeth and mandibular molars at 0.5-2 years of age and in all maxillary and mandibular teeth at 3-5 years of age. In commoner children, deciduous caries was seen in tooth types that have a low incidence of deciduous caries in modern Japanese. The present results show that deciduous carious lesions appear earlier and more frequently in the commoner children compared to the samurai children, probably because of differences in lifestyle between the two groups. There was no significant difference in the incidence of enamel hypoplasia in the deciduous dentition between samurai and commoner children, suggesting that the two classes had broadly comparable nutrition. In our previous study using the same skeletal series, similar results between samurai and commoners were found with respect to caries and enamel hypoplasia prevalence of the permanent dentition. Many of the samurai adults had slick polished teeth, which we believe were caused by regular brushing of the teeth in the samurai class. Such a custom might have functioned to prevent dental caries not only in the permanent dentition, but also in the deciduous dentition. Thus, oral hygiene practices in the samurai class are thought to have functioned to prevent dental caries not only in adults but also in children.

The use of bisphosphonates for osteoporosis patients has markedly decreased the incidence of femoral neck or trochanteric fractures. However, anti‐osteoporosis drugs have been reported to increase the incidence of atypical femoral fractures, which involve stress fractures in the subtrochanteric region or the proximal diaphysis. In this study, the morphological characteristics of the cortical bone in human femoral diaphysis samples were analyzed from individuals who lived before bisphosphonate drugs were available in Japan. A total of 90 right femoral bones were arbitrarily selected (46 males and 44 females) from modern Japanese skeletal specimens. Full‐length images of these femurs were acquired using a computed tomography scanner. An image processing method for binarization was used to calculate the threshold values of individual bones for determining their contours. The range between the lower end of the lesser trochanter and the adductor tubercle of each femur was divided at regular intervals to obtain 10 planes. The mean value of cortical bone thickness, periosteal border length, and the cortical cross‐sectional area was evaluated for all planes. Moreover, the ratio of the area of the cortical bone to the total area of cross‐section at the mid‐diaphysis was calculated. A comparison between males and females demonstrated that most females had lower cortical bone area ratios at the mid‐diaphysis. The femoral outer shape did not differ markedly according to age or sex; however, substantial individual differences were observed in the shape of the inner surface of the cortical bone. The cortical bone thickness and the cross‐sectional area decreased with age in the femoral diaphysis; furthermore, in females, the decrease was higher for the former than for the latter. This may be due to a compensatory increase in the circumference of the femoral diaphysis. In addition, in about half of the subjects there was a discrepancy between the region with maximal value of the cortical bone thickness and that of the total cross‐sectional area. Biological responses to mechanical stresses to the femoral diaphysis are thought not to be uniform. Bisphosphonates inhibit bone resorption and may promote non‐physiological bone remodeling. Thus, a nonhomogeneous decrease in cortical thickness may be related to the fracture occurrence in the femoral diaphysis in some cases. Thus, long‐term administration of bisphosphonates in patients with morphological vulnerability in the femoral cortical bones may increase the occurrence of atypical femoral fractures.

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