Table 1. Distribution of caries in finds of the mediaeval, Kamakura period (13-14th c., from Zaimokuza site, Kamakura City) Table 2. Distribution of caries in finds of the late mediaeval, Muromachi period (15-16th c., from Marunouchi, Tokyo) (39)

Table 3. Distribution of caries in finds of the early modern, Edo period (17-19th c., from Unko-in temple, Tokyo) Table 4. Distribution of caries in find of the early modern, Edo period (17-19th c., from Joshin-ji temple, Tokyo) (40)

Table 5. Distribution of caries in finds of the final Edo period (the latter half of 19th c., from Shirogane navy cemetery) (41)

Historical Changes in the Frequency of Dental Caries among the Japanese People Hajime SAKURA It is well known that the Japanese of to-day has one of the highest frequency of dental caries as other civilized peoples in the world. On the contrary, it has been reported that the caries were much less frequent among the prehistoric and protohistoric Japanese than among the recent Japanese. The aim of this study is to know the process of increase of caries through the time sequence from the ancient up to the present, by examining caries in the skeletal material of various historic periods between protohistoric and recent periods, and comparing the frequencies of them with each other. Methods The most common indices used in comparing the degree of caries occurrence among different populations are as the followings: (1) Ratio of persons having carious teeth =Number of persons who have caries/n, where N means the total number of persons examined. Sometimes is used "the ratio of jaws having carious teeth" calculated by the similar way, especially in the skeletal materials. (2) Ratio of carious teeth (R)=C/T, where C and T mean the number of carious teeth and the total number of teeth examined. (3) Caries frequency per person (CFP)=C/N. These three indices, however, do not mean much in such populations as skeletal material having a large number of post-mortem lost teeth. In such cases, (1) and (3) generally show lower values than the real ones. Index (2) also has a bias towards a higher value than the real one, because of such circumstances that the anterior teeth may be lost more easily than the posterior ones, although caries are found in the latter more frequently than in the former. This bias would become negligible if 32 kinds of teeth could be considered separately. Then, by summing up caries ratios in each of the different kinds of teeth, another index corresponding to unbiased CFP is computed. This has been defined as "the approximate estimate of the caries frequency per person (ACFP) " by the present author. ACFP can be calculated in three different ways: (A) By summing up caries ratios in each of the 32 different kinds of teeth: ACFP=R{1 }+R{ 1}+R{1 }+R{ 1}+*+R{ 8}. (B) By summing up caries ratios in each of the 16 different groups of teeth, grouping together the same teeth on both sides of the jaw: ACFP=2[R{1}+R{1}+R{2}+*+R{8}]. (C) By summing up caries ratios in each of the 5 different groups of teeth, (44)

grouping the same type of teeth on both sides and on both jaws together ACFP=8R{I}+4R{C}+8R{P}+8R{M1+M2}+4R{M3}. In these three methods of calculation, (C) has lower accuracy than the other two. In the present study, the ACFP is used as a useful index, to compare different populations. Intra-vital losses are not included in the number of carious teeth. Material and Results Five series of excavated skeletal remains covering a period from the 13th-14th century to the 19th century are used as the material for caries examination. Four of the five series each consists of adult individuals over two thirds of the whole population, some mature ones and very few seniles, except one from the Shirogane navy cemetery, most of the individuals of which are very young adults. The distributions of caries in these populations are shown in Tables 1-5. And comparisons of caries frequencies among the Japanese populations of various periods and the Ainus are made in Table 6. The ACFP of other authors' skeletal matelials also have been calculated in the same way by the present author. As to be seen in Table 6, the ACFP of the prehistoric Japanese appears to be 1 to 3, and that of the peoples in the protohistoric and Kamakura periods is not higher. Among the people of the Muromachi period (the 15th-16th c.), however, the ACFP is around 4, which is apparently higher than those of the former periods, and is not much different from that of the Edo period (the 17th-19th c.). The populations of the final Edo period and the recent Japanese represented in Table 6 mainly consist of very young persons, so the figures of ACFP and CFP of them are rather low. According to the reports of other investigators (NAGAO and TAKAKUWA, 1953; KITA et al, 1958), the CFP of the recent common Japanese over 25 years of age seems to be on a level around 7, which is much higher than those of the other periods. It can be recognized, therefore, that the increase of caries frequency in Japanese people is markedly rapid in two periods, the late mediaeval Muromachi period and the recent. These two increases are probably due to the changes in food habits, for example, the spread of artificial hard farinaceous food in the former case and the spread of sugar in the latter. In contrast with the Japanese, the ACFP of the Ainus in the 19th century are extremely low, 0.6 or less. But the CFP of the living Ainus in more recent times indicate higher values. It can be considered as the results of contact with Japanese civilization. General Institute Tokyo Medical & Dental of Legal Medicine, University (45)