A program for surveying dental hygienic status of rural populations having no dental service has been undertaken. The present paper concerns with the situation of Yonozumura inhabitants in the Prefecture of Ohita. Judging from its geographical location, distribution of the communities within the district, population scarsity and its poor socio-economic situation, it seemed utterly hopeless for these people to maintain any sort of dental facilities at their own expense, while in fact the dental health status as revealed in the present study pointed to an urgent need for such facility. The authors is of the opinion that some means of finacial aids from either the national, prefectural or village budgets should be taken into consideration to establish and partly maintain such an institution for the benefit of these people. The minor occurrence of tooth decay in the primary and middle school pupils as shown in the present study may be ascribed to their diet habit consisting of sweet potato and rye as staple food and generally rich in vegetable as compared to the dietary regimen of urban people.

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Age distribution studies have been conducted by Nohara for Osaka city (♂1588♀1342), by Ogata for Kumamoto city (♂2217♀1739) and by Urata for Kitakyushu city (♂1481♀1263) with reference to the deciduous teeth eruption in the younger populaiton of respective city. Based on the data obtained by these authors, geographical difference in the time of eruption of individual deciduous teeth was presented here by a special diagram for the purpose of clearer understanding. In the preparation of the diagram all the cases of eruption ages from the earliest to the most retarded ones were plotted by percentage values for the individual teeth. Any difference existing between tooth groups on both sides of the jaws was discarded from the diagram because of its insignificance found. The horizontal elongation of areas occupied by the individual teeth and the tilting of individual areas in this diagram represented the geographical difference of eruption age as well as the extent to which individual teeth divergently came into eruption.

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It is generally established that the time required for individual permanent teeth to come into full eruption range in relatively short period from 2 to 4 years of age. In the study to determine the average age of eruption for individual teeth, if one take one year period for the class unit of variances, there will always be danger to obtain one-sided data of frequency distribution giving incorrect knowledge of average eruption ages. In view of the above consideration, the average eruption time of permanent teeth was comparatively studied on two groups of data obtained from the same population of subjects taking either 4 months or 12 months for the class unit of variances. The results are summarized as follows. 1. It was suggested that the class unit of variances should be limited within 2 or 3 months period for the correct calculation of the average ages for the permanent teeth eruption. 2. For the correct calculation of ages for the first molar eruption, subjects older than 4 years should be selected and studied. 3. The aveage ages for the permanent teeth eruption were calculated as follows : in upper jaw, the first molar 80 months, the central incisor 86 months, the lateral incisor 99 months, the first premolar 111 months, the second premolar 126 months, the cuspid 126 months, and the second molar 147 months, in lower jaw, the first molar 79 months, the central incisor 79 months. the lateral incisor 84 months, the first premolar 117 months, the cuspid 120 months, the second premolar 124 months, and the second molar 136 months.

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A series of studies has been conducted in our laboratory on the anatomical features of the dental arch and the palate in the adult female. In the present communication, the palatal breadth, the mandibular alveolar breadth and the palatal arch length were examined on the male and female groups in Shimonoseki city, the female group in Yawata city, and comparison was made of the data obtained between both sexes groups in Shimonoseki city, between the two city groups and between both sexes groups in Tanushimaru, Fukuoka Prefecture. I. It was revealed that the palatal breadth, the mandibular alveolar breadth and the palatal arch breadth were shortest in the cuspid region, being increased toward the posterior region of jaws. II. Palatal Breadth The Palatal breadth in the female was conspicuously smaller than in the male of Shimonoseki group suggesting marked sex difference. It was also observed that the breadth in Shimonoseki female was smaller than in the male in Tanushimaru, although greater than the female groups of Yawata and Tanushimaru districts. III. Mandibular Alveolar Breadth There was also noted sex difference in the mandibular alveolar breadth of Shimonoseki group where that of the female was definitely smaller than that of the male. However, the value for Shimonoseki female was greater than that for Yawata female. IV. Palatal Arch Length Between both sexes groups of Shimonoseki the Palatal arch length in the female was definitely smaller than in the male. The value for Shimonoseki female was greater than either for Yawata and Tanushimaru female groups, although smaller than that for Tanushimaru male. V. Observation of the general aspect of the palate revealed that the palate in the female was smaller than that in the male in Shimonoseki group, but was greater than those in the other two female groups. There was no significant difference between Yawata and Tanushimaru female groups in this respect.

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