Of all the environmental factors of our life, drinking water has the greatest effect on our life. Consequently, it is essential to study the relation between drinking water and the caries of temporary teeth, which is of a great importance in the infant hygiene. Nevertheless, we have not seen any report on this study. From this point of view, we carried out medical group examination on the teeth of 1, 835 babies living in the central part of Tokyo and the Izu Seven Islands, who used rain water, underground watr or river water, during the period of 1956-1960. The following result was then obtained by making observation of the caries (def) classified by districts, sources of drinking water, ages, and also generally by the kinds of teeth and the surfaces of teeth.
The general observation of def classified by regions revealed that the rate was low for all agegroups in Central Tokyo, while high in the Oshima Island. This tendency was, in addition, remarkable in younger ages. The general observation of def by sources of water revealed the fact that rain water gave the highest rate, while surface water gave the lowest rat, for all ages. Besides, this tendency was most remarkable in two-year-old babies, in whom significant differences were noted as a result of the χ²-test. The observation of two-year-old babies classified by sources of water and kinds of teeth revealed that the teeth related with rain water gave the highest rate, then underground water followed, and river water the lowest, irrespective of the kinds of teeth. Moreover, the tendency was remarkable in the front teeth of the upper jaw and in the molar teeth of the lower jaw. Classified by the surfaces of teeth, it was generally found that the rate was the highest in rain water, then in underground water, and the lowest in river water, for every type of tooth surface. The tendency was remarkable in the occlusion part, incisors and molars on the upper jaw, molar teeth on the lower jaw, and in lower incisors for centripetal and centrifugal lips, cheeks, tongue and palate surface. Compared among the kinds of teeth and surfaces of teeth, def was the highest in the lip surface of the front teeth at the upper jaw, and the tendency was notable when classified by the sources of drinking water.
Thus it was discovered that there were characteristic relations among the caries of temporary teeth, region and sources of drinking water, and at the same time it was proved that drinking water played an important role in causing caries in temporary teeth.

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By comparing data obtained by a dental caries research team on the Scientific Research Program of the Ministry of Education in 1950, results of a dental disease public survey conducted by the Medical Affairs Bureau of the Ministry of Welfare in 1957, and significant differences between the school children of two Izu islands reported in a survey conducted in 1958, this writer made the following findings:
1) Among the school children on Hachijo Island, those between six and eleven years of age showed the highest dental caries rates, ranging from 82.1% to 96.0%.
2) Among the school children on Oshima Island, those between twelve and fourteen years of age showed the highest dental caries rate, ranging from 88.0% to 93.1%.
3) On Oshima, the dental caries rate for six-year-old school children was lower than on Hachijo Island, but no significant difference was noted between the two rates when these were considered in comparison with the national averages in the Ministry of Education and Ministry of Welfare surveys.

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In 1958 the National Society of Female Dentists conducted mass dental examination on Isu Oshima and Hachijo Islands. Utilizing data on the 1, 657 school children of six to fourteen years then examined, this writer tried the following techniques, with considerable success, as most effective and simple means of obtaining basic data for public health administration from community halth examinations: 1) with the reliability set at 95%, accuracy 5% and the percentage of healthy cases 15%, the number of mass-examined cases was determined by the following equation: n n₀/1+n₀-1/N, n₀=t²pq/d²
2) Numbers of cases were assigned on a doublebasis examination program with“area” and “age”taken as factors, and this allowed the mass-examinations to be conducted with ease.
3) After the mass-examinations, the results could be learnt mechanically.

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Utilizing data obtained in a dental disease public survey conducted by the Ministry of Welfare in 1957, this writer studied how the number of existing teeth changes in each sex and age group, and succeeded in estimating the number of existing teeth for each age group by the following equation, where X represents the age and Y, the number of existing teeth:
1) In males, Y=26.96+0.16X-0.006X².
At 17, 28 teeth; at 67, 13 teeth.
2) In females, Y=26.90+0.18X-0.007X².
At 17, 28 teeth; at 67, 8 teeth.
3) In general: Y=25.87+0.21X-0.007X².
At 17, 28 teeth; at 67, 10 teeth.
These tendency curves all proved highly significant through examination by the dispersion analysis method and showed good agreement with the examination results. The coefficients of interrelation between the age groups and the tooth number groups where as follows:
A) Male: r=-0.96±0.02
B) Female: r=-0.97±0.02
C) General: r=-0.96±0.02
Through examination it was found that P=0.001 in all these cases, showing that these values are significant. No significant difference was noted between males and females.

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This study is a continuation of“A Study on Statistics of Dental Caries”published in Japan Journal of Oral Hygiene, No. 1, Vol. 6, 1956.
Chapter I.
On the aggravation grade of caries, and the defective stage of dental substance, with special reference to“a scale for measuring the aggravation”.
We propose to use the following scale in order to measure the aggravation degree of caries. This scale has the advantage of being objective and quantitative, as compared with the usual classification which is subjective and qualitative.
i) volume of caries-capacity of defect in dental substance after the removal of soft dentine.
ii) carious surface, especially defect of masticating surface-defect of the surface of a tooth caused by caries, especially of the masticating surface.
iii) volume rate of caries=volume of caries/total volume of dental substance C₁= (0-6) %, C₂= (6-27) %, C₃= (27-100) %, C_M=100%
iv) rate of masticating surface defect=defect of masticating surface/total masticating surface C₁= (0-5) %, C₂= (5-100) %, C₃=100%, C_M=100%.
The author considers these characteristics will serve as the basis for the aggravation statistics of caries, statistics of dental ability, or evaluation of individual dental status.
Chapter II.
Statistics of caries aggravation
In Chapter I, we have pointed out the defects of usual statistics of caries aggravation, and having studied a method for ameliorating them, we have proposed a statistical measurement of caries aggravation.
In this Chapter we also derive diverse statistics from the proposed characteristics. As far as we know, no study in this field has yet been made; and this study is the result of the original idea of the author.
i) The following characteristics are used as the basis for measuring the aggravation grade of caries:
“volume of caries”,
“carious surface”,
“defect of masticating surface”.
ii) From these fundamental characteristics, eight following statistics are derived:
volume rate of caries,
defect rate of surface,
remaining rate of masticating surface,
aggravation velocity of caries,
aggravation rate of caries,
volume rate of healthy substance,
ability of masticating surface,
index of dental health and ability.
iii) These characteristics are calculating for all defective teeth, total teeth, by location and by person. Morever, we have also derived many statistics from them. The author belives these statistics are sufficient for the study of the process of caries.
iv) They will also serve as a convenient basis for comparing the resistibility of dentine against caries, a problem much discussed lately.
Chapter III.
Statistics of dental function, especially of the “ability of masticating surface”
We have studied the statistics of masticating ability, which is the most important part of dental statistics, and have also studied the ability of masticating surface which plays a fundamental role.
We have obtained the following conclusions:
i) It has become possible to classify the studies on masticating function into two groups, i. e., the one on ability, the other on efficiency. It seems to us the statistics on ability are less than those on efficiency. This is perhaps due to the difficulty and complexity of measuring.
ii) As the most important results on masticating ability, we may enumerate the calculation of contact point and surface by Dr. Yazaki, measurment of transparency of masticated wax plate by Dr. Manly, but all these studies on the decrease of masticating ability concern only with the change cause by a dental defect, and, as far as the author knows, no study has yet been made on the decreasing of masticating ability in the course of caries aggravation.

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