A one-year clinical study was carried out on 181 school children 6 to 11 years old to compare the caries-preventive effect of three commonly used topical fluoride agents: an acid phosphate-fluoride solution (2% NaF, 0.15MH₃PO₄, pH 3.6), an 8 percent aqueous stannous fluoride solution, and a 2 percent aqueous sodium fluoride solution.
Four groups -including the control group- were formed, each group representing as nearly as possible an equal cross section of the entire body of subjects.
The most careful procedure of topical application with a tray was used; applications were performed once yearly except in one group. This group was received topical application of a 2 percent aqueous sodium fluoride solution four times in two weeks according to the method of Knutson.
Considerable protection was afforded by all three of these agents, and especially by the acid phosphate-fluoride solution.

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Consumption of various kinds of soft drinks containing fruit juices has increaced remarkably in the past ten years in Japan. Most fruit juices contain large amounts of organic acids, and some experimental studies of the influence of these acids on human teeth have been reported. However, there have been few studies regarding soft drinks.
In this thesis the author examines the effects on human tooth enamel of some organic acids normally found in soft drinks, and discusses some countermeasures. Part I describes the methods employed: Part II compares the decalcifying effects of various kinds of soft drinks: Part III compares the effects of three organic acids-citric acid, tartaric acid, and malic acid-on human enamel powder: Part IV describes the effects of orange-flavored soft drink on human enamel powder: Part V describes the decalcifying effects of orange-flavored soft drink on human enamel powder that has been treated with fluoride compounds: and Part VI describes the decalcifying effects of orangeflavored soft drink on the enamel of deciduous teeth.
The author's findings are as follows:
1) Soaking the enamel of permanent teeth in various soft drinks and in citric acid showed that lemon drink caused the strongest decalcification, followed by orange, apple, grape and pineapple drinks, in that order. The decalcification caused by these drinks was stronger than that caused by citric acid solutions in which the pH was adjusted to the same value as the acid contained in each of the drinks.
2) Citric acid caused the strongest decalcification of enamel powder, followed by tartaric acid and malic acid.
3) The decalcification of enamel powder of both permanent and deciduous teeth caused by orange drink was stronger than that caused by citric acid. There was some slight indication that citric acid decalcified deciduous teeth more than permanent teeth, but there was no significant statistical evidence to support this. Soft drinks caused more decalcification of deciduous enamel powder than of permanent enamel powder.
4) Acid-proofing enamel powder of both permanent and deciduous teeth with a 2 % sodium fluoride solution and with Brudevold's II solution appeared to be more effective against the decalcification caused by soft drinks than against that caused by citric acid. Brudevold's II solution was more effective than 2 % sodium fluoride solution.
5) When deciduous teeth were soaked in soft drinks, the teeth treated with fluoride compounds were less affected than untreated teeth. In addition, Brudevold's II solution was decidedly more effective than 2 % sodium fluoride solution.

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Statistical observations conducted on the relationship between the prevalence of caries in deciduous teeth and bodily physical development in 1065 children between 3 years and 3 years and 1 month of age living in Tokyo between June 1963 and August 1964 revealed the following results.
1. Relationship between the prevalence of caries in deciduous teeth and the Kaup index.
The relationship between types of caries experience A, B and C in 3-year-old children according to the guide for dental health by the Ministry of Health and Welfare of the Japanese Government and the Kaup index classified into 5 groups, from 13 to 17 failed to show a significant difference among the groups. The ratio of types A, B and C was 2: 3: 0.5.
No significant difference was noted in each group according to the author's classification based on the number of carious teeth, type a (free carious teeth), type b (1-4 carious teeth), type c (5-8 carious teeth), type d (9-12 carious teeth), type e (more than 13 carious teeth). However, those with a low index or under poor nutritional conditions had numerous caries. The ratio of types b, c, d and e was 3: 4: 2: 0.5 except in groups 13 and 17.
The caries prevalence rate, the average number of carious teeth per child and the rate of carious teeth per total teeth present were calculated for each of the groups of caries classified according to the symptoms such as untreated teeth, caries 1st degree, caries 2nd degree and caries 3rd degree. In untreated teeth, C₂ and C₃, the group with a low index gave a significantly higher rate than the group with a high index.
2. Relationship between the prevalence of caries and body length at birth and growth of body length from birth until the present.
No relationship was found between the type of prevalence of caries and body length at birth and subsequent growth in body length. In the group with a short body length at birth, types a and e were frequently found in the number of carious teeth, but there was no significant difference in the degree of growth.
In untreated caries and caries separated according to symptoms, the group with large body length at the time of birth showed a somewhat higher rate of prevalence. In the degree of growth, as in the number of caries, no significant difference was found.
3. Relationship between the prevalence of carious teeth and body weight at birth and growth of body weight from birth until the present.
No positive correlation was noted between the type of prevalence of caries and body weight at birth and growth of body weight. In the type of caries number, types d and e appeared less frequently in children with good development of body weight.
In the untreated carious teeth and carious teeth according to symptoms, the ratio of caries was high in those with high body weight at birth. Regardless of the body weight at birth, the ratio of carious teeth was high in those with current poor development. The appearance of severe caries was especially high. Such a relationship was more pronounced in body weight than in body length.

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The color changes of human gingival epithelia offer an important information for the diagnosis of periodontal diseases. However, if observation is made with the naked eye, it is difficult to express the color correctly because each observer has some individual bias.
To prevent this fault in observation, the author devised a method in which the tone of gingival color was interpreted objectively by numerical values.
The author remodelled the ophthalmic fundus camera “Kowa RC-2”.
The gingiva was photographed on reversal color film, and the light extinction of a specified wave-length through the developed film was measured with an electric spectrophotometer.
The extinction curve showed two peaks at 440mμ and 540mμ in gingival photograpes.
As the extinction was higher at 440mμ, the measurement of color was hereafter made at this wave-length.
The results were as follows.
(1) The correlation between the degree of extinction of films and clinical PMA index was very high (γ=0.82).
(2) The greatest difference of light extiction between normal and pathological gingivae was found at the papillary and attached gingivae rather than at the alveolar mucosa and muco-gingival junction.
(3) In case of intact gingivae, no significant changes in the degree of extinction were observed by usual stimuli such as brushing or eating.
(4) The average extinction of buccal gingivae including molar teeth was not different from that of lingual (buccal) gingivae measured by a reflection mirror devised by the author.
(5) The values of light reflexion from the standard color paper the light extinction through the color film obtained frow it showed the same tendency. Moreover, the extinction degree method was far more sensitive than the former method.
(6) The extinction of color firm paralleled well the pathological conditions of the gingivae.
It started to drop after beginning clinical treatment and reached its lowest value after 20 days of treatment.

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