A cup of tea (containing about 0.49 mg F) containing soluble fluoride in the optimum necessary amount was recommended after every school lunch to 298 school children of Suhara in Sumon, Niigata prefecture, for about 250 days from December, 1975 to November, 1976. Increment lesions which appeared at three carious predirective sites, i. e., pits and fissures, proximal, and free gingival smooth surfaces of the children of the test school in the Suhara district were compared to the lesions found at the same sites in 185 children of three control schools in the Kamijo district of the same village. Reduction rates at each site were 52.8% for the pit and fissures and 57.2% for the proximal sites, but there was no reduction at the free gingival sites.

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The purpose of this study was to evaluate the clinical effect of a mutanase-containing mouthwash on the accumulation of dental plaque in a doubleblind cross-over investigation.
The teeth of twenty dental students were cleaned by scaling and tooth-brushing preceding two test periods of 1 week each. Oral hygiene measures were discontinued during the test periods, while the students rinsed their mouths thrice a day after each meal, one-half using the mutanase-containing mouthwash and the other-half using the placebo mouthwash.
At the end of each test period, the plaque accumulation was estimated. Statistical analysis of the data showed that less plaque accumulated during the mutanase than during the placebo period when analysed on all surfaces of all teeth. (P<0.02). The mutanase mouthwash was more effective for the lingual than for the labial or buccal surface of the tooth arches.

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Veillonella, a strict anaerobe, which is one of the constituents of the habitual oral microflora, is known to have the strongest nitrate reduction ability of the oral microorganisms.
The author isolated some Veillonella from human saliva and identified them as two species, V. alcalescens and V. parvula. Each Veillonella was inoculated and cultured in a medium containing nitrate. The concentration of nitrite produced by the action of nitrate reduction and the turbidity in the growth medium were measured. The processes of nitrate reduction was compared in the two Veillonella species in regard to the nitrite production, the bacterial growth, nitrate reduction ability, and nitrite reduction ability in the medium.
The difference of nitrate reduction between V. alcalescens and V. parvula was not obvious in the logarithmic growth phase, but it was clearly demonstrated in the stationary phase, where the nitrite reduction was observed only in V. alcalescens. However, it was also found that V. parvula acquired nitrite reduction ability when it was cultured under aerobic conditions. This change in V. parvula seemed to be related to catalase action.
Nitrate reductase activities of Veillonella were present mainly in the membrane-bound fraction at both the logarithmic and the stationary phases. But cytoplasmic nitrate reductase activities increased exceptionally at the stationary phase in V. alcalescens.
From these results, it seemed that V. parvula showed the respiratory type of nitrate reduction, whereas V. alcalescens showed both the respiratory and the assimilative types; the respiratory type appeared at the logarithmic phase and the assimilative one mainly at the stationary phase.

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In order to clarify the epidemiological features of occupationally acquired hepatitis B virus infection in japanese private dental practitioners, the author carriedout a questionnaire survey (n=2, 356) and serological survey (n=209). HBs-Ag and HBe-Ag in saliva (whole and parotid) of hepatits B virus (HBV) carriers (n=36) were also investigated to study the saliva as a source of infection. HB-antigen and antibody were determined mainly by solid-phase-radioimmunoassay (RIA).
The following conclusions were obtained:
1) The incidence of hapatitis (including jaundice) in japanese private dental practitioners in the questionnaire survey was 16.8%, and a higher rate of incidence was seen in the higher age groups. The occurrence of hepatitis (including jaundice) was at the age of 36.4 years (mean). 44.7 % of the dentists who had been practicing more than 10 years had contracted hepatitis and the mean occurrence period was 8.9 years.
2) The incidence HB infection in Japanese private dental practitioners in the serological survey was 48.4 % (positive to HB-antigen and antibody), which was significantly higher than the controls (p<0.05). A higher rate of positive antibody reaction was seen in the higher age groups. An acquired immunity against HB was obtained within 20 years of practice which may protect the dentists from the HB infection.
3) HB infection in Japanese private dental practitioners tends to a lateral infection during the dental treatment of hepatitis patients. By the application of the prevalence theory of Reed-Flost, it was calculated that 35 to 40 HBs-Ag positive patients may be treated by a Japanese private dental practitioner per year.
4) Considering the occult blood reaction in saliva, the HBs-Ag in saliva may originate mostly from the blood. Thus, pure saliva may not contain the HBs-Ag. However, since HBe-Ag originating from blood was identified, it is possible that the saliva is one cause of HB.
From the consideration of the questionnaire and serological surveys, it seems reasonable to conclude that Japanese private dental practitioners have been infected with HB at a high rate. Therefore, anti-HBs serum or inactivated HB-antigen-vaccine might be required to prevent the disease.

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The air compressor is one of the many instruments frequently used in dental treatment. The air coming from a compressor must be clean, for it is used for treatment in the oral cavity.
As a matter of fact, however, the air is not always clean or sterile as confirmed by our studies and there have been published other studies to the same effect. On the other hand, the literature is still scanty concerning countermeasures for this problem.
In the present report, we studied the effectiveness of a Puretron in supplying pure air to the dental unit through the elimination of dust particles, bacteria, and water drops in 2 selected dental clinics.
The effectiveness of dust depuration was measured with a Royco 202 airborne particle monitor in which the particle sizes were classified into 15 groups, the effect iveness of sterilization was examined with a SY model pin hole sampler, and the effectiveness of dehumidification was also studied. The following conclusions were obtained.
1. The effectiveness of dust depuration in our laboratory was found to be 100% over 15 microns and, in a dental clinic used for the present experimental purpose, it was 100 % over 2.0 microns.
2. As regards the rate of bacterial elimination, it was 99.6% in the laboratory, whereas it was 100% in the dental clinic.
3. The effect on Serratia marcescens through a spray procedure proved to be 100% when the number of bacterial colonies was 3.60±0.34 pieces/l in the intake part of the Puretron.
4. As for the effect of dehumidification, the humidity after having passed through the Puretron was 36% in all the cases under study.
In view of an assumption that these instruments will play a greater role in dental treatment in the future, it is desirable that an instrument capable of a higher degree of elimination of dust particles and sterilization should be developed.

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