This study was the result of three successive experiments that started from 1959, 1960 and 1962. Only first grade children of the primary schools in Tokyo and Yokohama city were used for the experiment.
Experiment 1959: -
The children who had lower first permanent molars free from carious lesions were selected from 16 schools. These children totalling 1.221 were divided into three groups, i. e., 2% NaF group, 4% SnF₂ group and the control group independently in Tokyo and Yokohama area. All children were recieved dental prophylaxis and the children of experimental group were applied with respective fluoride solution for three minutes according to Knutson's method. The control group was similarly treated with distilled water. The treatment of all groups were carried out four times within one month.
After two years, the 23 per cent (Tokyo) reduction and the 33 per cent (Yokohama) reduction were shown in children who were treated with 2% NaF as compared with the control group being evaluated by DMFT. In 4% SnF₂ group, there were 20 per cent reduction in Yokohama, area, but no reduction in Tokyo area. These reduction were considered statistically significant at 1% level by Chi-square test.
Experiment 1960: -
The children totalling 994 were selected from 24 schools similarly as in 1959, and were divided into four groups that were 2% NaF, 2% SnF₂, 8% SnF₂ and the control group. All children were recieved dental prophylaxis and topical application of respective fluoride solution or distilled water (in the control group) according to Muhler's method. Two per cent NaF group and 2% SnF₂ group were recieved four treatment during one month, but the control group and 8% SnF₂ group were recieved a single treatment.
After two years, the reduction of new carious teeth in 2% NaF group were indicated as 39 per cent (Tokyo) and 23 per cent (Yokohama) when compared with the control group. Per cent reduction of the SnF₂ group versus the control group were indicated as follows, 2% SnF₂ group was 16 per cent (Tokyo) and 6 per cent (Yokohama); 8% SnF₂ group was 27 per cent (Tokyo) and 15 per cent (Yokohama). Two per cent NaF group in Tokyo and Yokohama and 8% SnF₂ group in Tokyo were considered to show the significant reduction, but in other groups it was not significant (at 1% level).
Experiment 1962: -
The children in a school totalling 132 in Yokohama city were divided into two groups. The experimental group were recieved a single application of 2% NaF solution followed by a single application of 8% SnF₂ solution on all the teeth after the dental prophylaxis. The latter treatment was applied in the following seven days. The other group served as the control without treatment.
After one year, 57 per cent reduction (a significant difference at 10% level) was shown in this group evaluated by DMFT incidence, but after two years, there was indicated only 13 per cent reduction which was not statistically significant.
In Yokohama city the children of six schools totalling 819 were divided into two groups. The experimental group was recieved a single application of 8% SnF₂ solution on all the teeth after the dental prophylaxis, and control group was not treated. After one year, the 4 per cent or 7 per cent reduction was shown according to the DMFT incidence per capita or the DMFT percentage. After two years, there was no reduction being evaluated by DMFT incidence. These reduction were not considered to be significant.
One of the reasons of apparently lower percentage reduction in SnF₂ group might be attributed to the pigmentation on the fissures and pits after the stannous fluoride treatment, which were wrogly diagnosed as carious lesions and filled by the dentists in practice. To support this assumption, the filling teeth ratio in the SnF₂ group was actually increased.

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Antibacterial activity in human saliva against species of lactobacilli has been described by Zeldow, Matsumura et al and Dogon, Kerr and Amdur In each study this activity was demonstrated in either BS agar or LBS broth.
Bartels and Blechman attempted to observe this antibacterial activity on other nine kinds of medium, and failed to demonstrate the antibacterial activity on the selected media. Reasons for a variations in the antibacterial activity of saliva on the selected media have not been clarified.
Ueda et al in this laboratory have reported that an inhibitory substance on the activity of the S.A. Factor, the S.A.F. depressor, contained in human serum was identified as a serum albumin, and that reactive sulfhydryl groups of the albumin as well as other -SH compounds played an important role on demonstrating the depressor activity.
This paper is concerned with the presence of reactive -SH group, as a S.A.F. depressor, on selected media.
As the results, the activity of the S.A. Factor, against Lactobacillus plantarum ATCC 8014, was demonstrated in LBS broth, and was scarcely observed on selected media such as trypticase soy broth, brain heart infusion broth, nutrient broth, Todd-Hewitt broth and Sabouraud maltose broth. Partial regeneration of the activity, however, was obtained on the selected media by an addition of -SH group reagents.
Complete regeneration of the activity was observed on trypticase soy broth with a -SH reagent CuSO₄. The activity of the S.A. Factor regenerated with CuSO₄ in trypticase soy broth was apparently decreased on addition of mercaptoethanol which is a powerful reducing agent of sulfur.
A depression of the activity on selected media appears to be due in part to the reactive -SH groups contained in the media.

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Significance of changes in the teeth especially Hutchinson and Fournier teeth among student of schools for the blind and deaf was reported from our Department about 10 years ago. In order to assess the recent situation, 124 students were examined in a school for the blind concerning the intraoral state from an odontological point of view.
Abnormalities in the development and morphology of the teeth, degree of carious state, pyorrhea, state of the cleaning of the oral cavity, presence of deposition around the teeth, and relationship with diseases of the eye were investigated. No difference was found between students in the school for the blind and other healthy subjects concerning the degree of carious state, alveolar pyorrhea, state of the cleaning of the oral cavity, and deposition around the teeth. In 4 students Hutchinson and Fournier teeth were noted simultaneously, while Hutchinson teeth alone were noted in 1 and Fournier teeth alone were seen in 8. Among those, congenital complete or almost complete blindness was seen in 8 and acquired complete or almost complete blindness was seen in 5, indicating a pronounced decrease as compared with the result of 10 years ago.

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Relation between commencement of menstruation and tooth development in ninety-one girls in a primary school in Kumamoto City who were in the 6th Grade in 1965 was studied, with resultsas follows:
1. In early cases, menstruation begins at 9 years and 11 months of age; menarche increases from about 11 years and occurs in large numbers during 11 years and 10 months and 12 years and 3 months. That is, 34.07% of the girls had the menses before they finish primary school.
2. Dental condition at the time of menarche was as follows:
a) In general three or more second molars had erupted before menarche. Its percentage was 77.41%. At least the bilateral second molars on the lower jaw had erupted before the first visit of the menses in all the case.
b) Presence of remaining deciduous teeth was investigated, with the result that 80.65% of the subjects had no deciduous teeth in their jaws. Even if there was any, it was supposed to be not more than one.
It was considered that, along with the growth in stature, degree of tooth development may be used as an indication of the time of menarche.

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Kikuchi City has been said to have the largest number of pupils having carious teeth. The following investigation was made by the Research Group of the Association in order to clarify their actual condition.
Material was the records of oral examinations in a total of 3774 pupils in all the eleven primary schools in Kikuchi City, and soley the so-called 6-year-old molars were investigated, counting both treated and untreated teeth, and a child having either one molar or even four (upper, lower, left and right) molars affected by caries as a head.
1. The caries incidence rate per head of the 6-year-old molars in the pupils of oll the primary schools in Kikuchi City in 1965 was 71.11% (_??_67.51, _??_74.93). Also the per-head-percentage of the carious 6-year-old molars which had been treated on was 40.99%, while its per-tooth-percentage was 52.33%. It is rather good, but is far from an idealistic dental service.
2. In this study the city was divided into four parts, the mountain, the mountain with some paddyfields, the business area, and the level area mostly paddy-field. The highest rates of caries incidence in the 6-year-old molars at different age levels always were those in the business area, the part of the mountain with paddy-fields closely following. Then the mountain, and the lowest rates always were those in the level area.
3. The caries incidence percentages of the 6-year-old molars per head and per year of entrance to school were: the 1st graders in 1960 was 16.00%, while those in 1965 was 38.39%, the latter being approximately 2.6 times as much as the former.

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A statistical investigation on dental caries in the so-called 6-year-old molars in 36, 909 (_??_ 19, 011, _??_ 17, 898) pupils in 45 primary schools in Kumamoto City, Kumamoto Prefecture, was made by the Research Group in the Association, using “Records of Oral Examinations in the Primary Schools, 1965”. All the 6-year-old molars in these children which had been affected by caries at all were counted regardless of their being treated or not, and a child having either one or four (upper, lower, left, and right) carious molars was counted as one head. The result was a follows:
1. The caries incidence rate of the permanent first molar in the pupils of all the primary schools in Kumamoto City was 52.11% (_??_ 48.23%, _??_ 56.22%), and in area levels, the highest rate was that of the mountainous area, followed by those of the residencial, farming, and business areas, between the latter two, however, hardly any difference was observed. The actual incidence rate for each school varied so much that no classification was possible.
2. The ratios of the carious 6-year-old molars in all the primary school pupils in Kumamoto City were: 1st graders 19.17%, 2nd graders 20.88%, 3rd graders 17.67%, 4th graders 12.42%, 5th graders 9.65%, and 6th graders 8.72%. That is, the majority, 62.2%, of these molars were attacked by caries during the 1-3 Grades. This tendency was remarkable in schools having high ratios.
3. The caries incidence rates of these pupils in past years were also studied, resulting in the findings that every year the ratio of the 1st graders was higher than that of the previous year. While it was 12.17% in 1960, it was 20.64% in 1965, indicating increase of approximately 1.7 times during the past six years. The difference in the ratio resulted from this yearly increase continued unchanged as the newly entered pupils grew up to be 6th graders, showing clearly parallel lines.
4. The percentage of the permanent teeth affected by caries per head of the pupils in Kumamoto City was 35.67%, while that of per tooth was 54.93%. Although this condition is rather good compared to those in other districts, it is still very far from the perfect treatment on children's teeth.

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Ratios of caries incidence per head in children living in minor cities, and villages in rural district, mountain, and coast in Kumamoto Prefecture were investigated by the use of “Records of Oral Examinations, 1965” of 11, 704 pupils (_??_ 5, 907, _??_ 5, 797) in 30 primary schools, chiefly concerning the affected permanent first molars. In this statistics, all six-year-molars that had been attacked by caries were counted regardless of their being treated or non-treated, or slightly or severely affected, and when there was a single affected first molar in an oral cavity or four (upper, lower, right, and left), it was equally counted as one.
1. Observation by district: The highest ratio of the carious six-year-molars in primary school pupils by districts was unexpectedly that of the pupils in mountain villages, followed in the order by minor cities, farming villages and fishing villages. In Kumamoto Prefecture as a whole, there was little difference between the ratios in Kumamoto City and minor cities. Also, very little difference was observable in a more detailed comparison between the ratios in the agricultural areas in Kumamoto City and those in simple farming villages in rural districts. In short, the number of children having carious permanent first molars has already increased to high ratios all over the prefecture without distinction between rural and urban districts.
2. Frequency of caries attack on the permanent first molars in pupils in the abovementioned minor cities and villages was observed in relation to their chronological ages, with the result that the higher the ratio of caries incidence per head of the district, the larger the number of permanent first molars attacked by caries during the first few years in the primary school. This fact seems to be a general principle.
3. Observation of the relation between the six-year-molar caries incidence rates and the year of entrance to school was made in children in simple farming villages. While the percentage of children having caries-attacked first molar among the 1st Graders of the year 1960 was 12.98%, that of those in 1965 was 19.86%, that is, increase of 6.88% (1.53 times) during the six years. In other words, the ratios in the 1st Graders has shown approximately 1.0% of increase every year. Furthermore, number of the affected first molars in all graders increase year after year as they grew up, showing parallel ascending curves. This phenomenon is similar to those in children in Kikuchi City and Kumamoto City described in the previous report.

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