The present study was conducted for the purpose of elucidating the correlation of three items: i) the frequency of toothbrushing, ii) the degree of dental cleanliness, and iii) the PMA index for a three-year period till the graduation of the subjects from lower secondary school. The subjects were instructed to brush their teeth thoroughly in the inital examination of each year, and their oral conditions were examined for a total of 13 times, on an average of 3 to 5 times per year.
When the correlative coefficient (r) was calculated based on the study, there was observed a weak minus correlation between the frequency of toothbrushing and the degree of dental cleanliness but there was no statistical difference between the frequency of toothbrushing and the PMA index, the statistical difference being about 1% risk level between the frequency of toothbrushing and the PMA index.
When the 1975 data were analyzed concerning the above items, the correlation between the degree of dental cleanliness and the frequency of thoothbrushing and the PMA index was given the main attention. As a result, it was found that the correlation between the degree of dental cleanliness and the PMA index was +0.320-+0.578, with a fair degree of positive correlation.
The correlation, on the other hand, between the degree of dental cleanliness and frequency of toothbrushing was slight, with a value of -0.084- -0.198.
As stated above, a total of 314 children were subjected to the study for a consecutive period of three years. But some of the subjects were for a period of two years.

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The present study was made for the purpose of reinvestigating the safty of fluoride mouth rinse, the possibility of caries-preventive effect and the rinsing method itself by determining the amount of fluoride that remains in the mouth after the use of fluoride mouth rinse.
A total 80 children in the third grade of primary school (consisting of 44 boys and 36 girls) were selected as subjects. They were instructed to rinse with 10ml of the fluoride mouthrinsing solution (containing 500ppm of F^-; pH 5.0, phosphoric acid-acidified NaF solution) that had been exactly measured for 30 seconds, and then rinse the mouth twice with 10ml of distilled water for 10 seconds at a time. The fluorine content of the portion of the agent that remained in the rinsing cup, the amount of fluorine that was spit out after use of the rinse, and the fluorine content of the rinsing distilled water were determined. For the determinations, an ORION ion meter (model 801) and fluoride ion activity electrodes were used.
As a result, the sum of fluorine content of the portion of the rinsing agent that remained in the rinsing cup and the amount of fluorine that was spit out was 4.69±0.12mg in the boys and 4.58±0.12mg in the girls, corresponding to 93.79% in the boys and 91.52% in the girls of the amount of fluorine that had been given.
Using the conventional rinsing method, the amount of residual fluorine in the mouth was 0.31±0.12mg (6.21%) in the boys and 0.42±0.12 (8.48%) in the girls. When the use of fluoride mouth rinse was followed by a rinsing with water, the retention of fluorine was 0.16±0.12mg (3.13%) in the boys and 0.27±0.12mg (5.46%) in the girls. In 65 children, corresponding to 81.3% of the total 80 children, the retention of fluorine after use of the conventional fluoride mouth rinse was less than 0.5mg.
From these findings, it was proved again that the fluoride concentration and volume of rinsing solution is entirely safe provided the rinsing method is adequate, and fluoride mouth rinse is an effective fluoride application method for the prevention of dental caries.

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When cavities are prepared in clinical practice, the outline form is generally established by following the law of extension for prevention advocated by G.V. Black, who placed stress on the unclean area and immune area of tooth surfaces. In this case, not much consideration has so far been given to caries immunity of the oral environment, that is, caries susceptibility. So it seems to be reasonable that the concept of caries susceptibility is introduced into the conventional cavity preparation.
The purpose of this study is to investigate the proper testing methods for determining individual caries susceptibility which could be an effective measure when preparing the cavity under the law of extension for prevention. Thus, attention was focussed on the acid buffering property of saliva as an environmental factor and the acid solubility of enamel as a host factor.
In this article, the effect of storage conditions of saliva on acid buffering capacity was first studied and then a unique method for the buffering capacity test was devised and its availability was examined.
The results were as follows;
1. Saliva stored for 3 hours in air showed considerably higher pH and acid buffering capacity than saliva stored for 3 hours without air or saliva immediately after collection. In the conventional measurement of the buffering capacity in air, pH values of the salva increase depending upon the amount of stirring and subsequent standing time, and are unstable. A quasi-anaerobic measurement of the buffering capacity was therefore designed.
2. A special apparatus with a Beckman pH combination electrode fitted in the piston of the injection syringe was devised. In the measurement, pH of the saliva (1ml) sucked through the injection needle was read (initial pH) and then was again read after suction of 0.1ml of lactic acid and stirring (final pH). Final pH/initial pH was expressed as the value of the acid buffering capacity.
3. According to the new method, the pH and the buffering capacity of the same individual were stable with several measurements of different saliva.
4. The pH and the buffering capacity of saliva stored for 3 hours without air were the same as those of saliva immediately after collection.
5. When the pH and the buffering capacity of saliva of the same individual were determined in the spring and autumn, the values of both salivas did not show any difference.
The new method presents good reproducibility of the pH value of the saliva, and proves to be available for the buffering capacity test.

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This study was attempted in oder to design a new acid solubility test of tooth substances for clinical practice. Therefore, an acid-agar cylinder containing the Fiske-Subbarow reagent (named“FS-Agar”) was newly devised, and its application was also evaluated. This agar is developed to a blue color by phosphorus.
1. The density of developed color of FS-Agar increased in proportion to the given amount of inorganic phosphorus added. The color development in blue was recognized even by such a quantity of phosphorus as 0.1 μg.
2. Using the facial surfaces of the permanent teeth, phosphorus was determined by the color-developing technic with FS-Agar applied at the mesial halves and calcium was determined by the microspectrometric method with acid-agar applied at the distal halves. A significant correlation was found between the dissolving tendency of phosphorus and the amount of dissolution of calcium.
3. FS-Agar which was applied on the surfaces with and without fluoride treatment showed significant difference of acid solubility between both treatments.
4. The newly devised color developing method with FS-Agar proved to be easier and more practical than the other tooth acid solubility test with dissolved calcium.

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Predicting the tendency of caries susceptibility in the individual mouth seems to be very important for preparing cavities, selecting restorative materials and technic, and giving health care to the patients.
In this study, the test for buffering capacity of saliva newly designed in Part I, and the test for acid solubility of tooth substances and the additional measurement of inorganic phosphorus of saliva with FS-Agar designed in Part II were applied to the pupils of primary and junior high schools, and to the adults in oder to find an effective test for determining caries susceptibility.
The results were as follows;
1. Acid solubility of tooth substances did not show any relations to DMFT and new DMFT.
2. The amount of inorganic phosphorus of saliva was closely related to only DMFT. On the other hand, there was a close relationship between the buffering capacity and new DMFT.
3. Regarding the adults, the buffering capacity of saliva had significant correlation with DMFT, but the amount of inorganic phosphorus of saliva had only a slight correlation.
4. The buffering capacity test newly devised appeared to be quite useful for examining caries suceptibility, after various factors were discussed. Tentative criteria based on the buffering capacity of saliva were thus considered for the treatment planning of carious teeth or the mouth. However, the degree of DMFT should not be overlooked because the tendency of caries susceptibility are somewhat reflected in the degree of the DMFT, particulary in acults case.
5. Further study should be attemyted in oder to establish clear criteria for clinical practice.

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A recent problem is mercury pollution of river and fish, and the allowable level of mercury in waste water has been fixed at below 5 ppb. Environmental mercury contamination through dental procedures, especially through waste water from dental offices, was studied and the following results were obtained.
1) High levels of mercury were contained in saliva vacuumed from the oral cavity during amalgam filling, but mercury levels were decreased by using a net bag for removal of amalgam scrapings.
2) Mercury was detected in all waste water from dental practice, such as saliva vacuumed from the oral cavity, water gargled after amalgam filling, waste water from the dental unit, and the final waste water from dental offices. As the amount of flowing waste water increases, mercury levels in waste water decrease. But the amount of mercury discharged from dental practice through waste water was not small.
3) Mercury levels in final waste water from dental offices were at an average of 11.3 ppb. The final waste water of almost all dental offices exceeded the allowablelevel (5 ppb).
4) Mercury levels in soil around dental offices, and even in soil of houses next to dental offices, was higher than control houses. Then it was shown mercury contamination in dental practice was caused not only through waste water but also through the atomosphere.
5) Very high levels of mercury was contained in soil soaked in waste water from dental offices and in sludge from drain-pipes of dental offices. It was shown that soil and sludge absorb and concentrate mercury in waste water.
6) There is almost no risk that mercury metal discharged from dental offices will be converted to more poisonous methylmercury by the action of microorganisms in soil and sludge.
A large amount mercury metal is discharged from dental offices, and it is absorbed, accumulated, and concentrated to very high levels in soil and sludge. Therefore we should strive to find a practical method of extracting mercury from dental waste water.

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In a previous study we have demonstrated that a bacteriolytic enzyme from Streptomyces globisporus inhibits dental plaque formation in man. This paper describes the effects of the enzyme administration into the oral cavity on the relative proportions in population of 8 selected genera of microorganisms indigenous to human dental plaque and tongue coating.
Eighteen volunteers, males and females aged 19 to 30, were divided into 2 groups, the enzyme and the placebo. The Enzyme was administered by inserting a chewable tablet with or without the enzyme (9mg/tablet) under the tongue. The volunteers were instructed to take 2 tablets after each meal, 6 tablets a day, for 20 days, and to refrain from brushing the 6lower anterior teeth during the experimental period. On day 3 and 20, samples of dental plaque and tongue coating were collected from the labial surface of the lower right canine with asterile spoon excavator and from the dorsal surface of tongue with a sterile cotton applicator. The relative proportions in population of 8 selected genera were determined by comparing numbers of colonies recovered on selective media under appropriate cultural conditions.
Streptococcus was a major component of dental plaque of day 3 (80% of total colony forming units), and Neisseria (3.0%), Veillonella (7.7%), Corynebacterium (5.2%), Actinomyces (3.4%) and Fusobacterium (1.0%) were consistently recovered in the ratios given in parenthesis. With the development of plaque, Streptococcus (63%) and Neisseria (0.1%) decreased, while the remainder, particularly Corynebacteriurm (20%), appeared to increase in the relative proportions of populations. In tongue coating as well, Streptococcus (70%) was predominant. Actinomyces (0.8%) and Corynebacterium (1.3%) were present in lower proportions, and Neisseria (9.7%) and Fusobacterium (3.4%) in greater proportions, in tongue coating than in dental plaque. The increments of Veillonella (12.5→20%) and Fusobacterium (3.4→5.7%) compensated for the reduction of Streptococcus (70→61%) in day-20 samples. No significant difference in the relative proportions of genera other than these two existed between day-3 and day-20 tongue coatings. The proportions of Candida were negligible in all samples of the dental plaque and tongue coating. Lactobacillus was recovered in extremely low numbers from only a few samples of tongue coating.
The relative proportions of the selected organisms detected in dental plaque and tongue coating were not affected by the intra-oral administration of the bacteriolytic enzyme for 3 and 20 days. Streptococcus mutans also, although highly sensitive to the enzyme in vitro, did not decrease in proportion.

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I studied a sample of 159 workers employed in various departments of a battery factory, so that adequate measures for prevention of occupational dental disease and workplace reassignment could be established. Workers in an environment where acid fumes were produced were studied by the macroscopic method established by our laboratory and by the replica method of Hayashi (G₀-G₄). Further, the same workers were subjected to a four-year consecutive study for a comparison of the results of the two methods. The volume of acid in the work environments under study was 0.475mg/kg on the average, which is much lower than the maximum permissible standard of 1mg/kg. I obtained the following results:
1) About half the workers under study complained of some dental disease or other. These inclueded such complaints as stinging pain in the anterior teeth when inhaling cold air, stinying pain in the anterior teeth when at work, and occasional unpleasant feeling in the front teeth.
2) In terms of age, the majority of those who complained of dental disease were in their twenties. However, in terms of the length of time they were engaged in this occupation, the majority fell in the 6 to 10 year bracket.
3) More diseased teeth were found in the mandible than in the maxilla, disease occurring most often in the mandibular central incisors. The incidence of disease in the maxillary incisors was small. The percentage of diseased teeth increased in proportion to the number of years spent in the occupation.
4) Although the findings of the replica method gave a high distribution for G₂ and G₃ (77.5%) in the first year, with the passage of time G₂ decreased while G₃ increased.
5) With regard to individuals during the four-year suvey period, the percentage of diseased teeth increased linearly with the passage of time. Although the subjects worked in an environment containing less acid than the legal limit, acid erosion of their teeth was observed when they continued in their occupation for a considerable length of time. With the replica method, it was possible to observe the transition from G_0·1 to G₃.
6) When comparing the marcroscopic and replica methods, 48-65% of the macroscopically normal cases (E₀) and 70-80% of the macroscoscopically dubious cases (E_±) were found the be G₂ or G₂ when examined by the replica method.
7) Since it is possible to discover early cases of acid erosion by microscopic examination with the replica method, workers can be reassigned to a safer place of work either immediately or later, depending on the degree of the erosion.

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