The purpose of this study was to evaluate the health activities in Hiraizumi primary school, Iwate prefecture. As a result of intensive dental health activities from 1978 to 1990, which consisted of tooth brushing instruction by class, dental education for the schoolchildren and their guardians, utilization of fluoride mouth rinsing (once a week), and, by following a model school of caries prevention designated by the Ministry of Education et al., the oral health status of the Hiraizumi primary schoolchildren improved significantly compared with those of the Ohya primary schoolchildren who followed the routine school dental health activities. The results of questionnaires, taken from both primary schoolchildren in 1986 and 1989, show that the oral health behavior of the Hiraizumi primary schoolchildren also improved.
We performed a clinicostatistical study of the maxillofacial fracture due to sports during the period of 15 years between 1977 and 1991. Eighty-nine patients were seen with injuries resulting from 21 different sports. The incidence of the fracture was most common in rugby, followed by ski, baseball and soccer. Males were shown to be more prone to maxillofacial fracture than females (5. 4: 1) and the highest incidence of injuries involved the 20-29 age group followed by the 10-19 age group. The major parts of the fracture were the mandible and the alveolar process. Conservative therapy such as maxillomandibular fixation was usually performed and the clinical course was good. It was suggested that the prevention of the sports-relatedfracture and the time of returning to sports after the fracture will require further study.
Dental caries was experimentally induced in the Ishibashi rats (ISR) by feeding them with conventional diets or with caries-producing diets, and the pattern and severity of their induced carious lesions were compared with those of the Sprague-Dowly rats (SD) . Simultaneously, serum antibody titers against Streptococcus mutans and calcium and phosphorus concentration in the sera and in the femurs were compared between the ISR and SD. The results were as follows: 1. When judged by cavities, ISR showed a higher carious incidence and average number of cavities per one rat than the SD, whichever diet the rats were fed. 2. When judged by fissure caries observed on the thin sections of the teeth, both the carious incidence and average number of fissure lesions in the ISR were not always high compared with those in the SD, and there seemed to be a great variation of cariessusceptibility in the ISR. 3. Caries in the ISR seemed to be more progressive than that in the SD. 4. There were no differences in the serum antibody titers against the S. mutans between the ISR and SD. 5. No differences in the concentration of calcium and phosphorus in the sera and femurs were observed between the ISR and SD, whichever diet they were fed.
The present study was carried out to investigate the alveolar bone resorption in the molar tooth region in the rats fed a low calcium diet. Male Wistar rats (70-85g in body weight) were either fed a low calcium diet (0.05% Ca, 0.35% P) or a control diet (0.5 % Ca, 0.35% P) by using a pair feeding technique. The rats were sacrificed at intervals of 3, 6, 9 and 20 days during the experimental period. Contact microradiograph of the second molar region of the mandible showed that the cancellus bone as well as the endosteal surface of the cortical bone were progressively resorbed soon after the start of low calcium feeding. At day 9, the amount of bone was reduced to about half of the control rats and 80% of the bone was diminished at day 20. In spite of the severe bone resorption, the alveolar bone proper that surrounds the molar sockets and a few cancellus bone were seen remaining and the occlusal function of the molar tooth seemed to be maintained. These results suggest that the alveolar bone quickly responded to the low calcium diet resulting in bone resorption and that the bone in the supporting tissues of the molar tooth seems to be not affected by the calcium deficiency.