Oral hygiene has been widely cared of by means of a mechanical and physical practice with tooth-brushes as a daily habit. But conventional methods cannot be effective enough, as the fact of a recent increase in caries and periodontal diseases has shown.
The author considered it necessary to approach oral hygiene from aspects of chemical and biochemical actions in addition to from conventional aspects of mechanical and physical ones. Therefore, Dextranase, expected to have mentioned new effects, was added to a dentifrice, and another dentifrice not containing the above agent was used as a control, and two problems, how effective it would be and if it would be safe or not, were examined.
Fifty-eight healthy adult women were selected as subjects: 29 of them were asked to use a dentifrice containing Dextranase for continually one month; rest of 29 were asked to use a control dentifrice for the same period.
A health examination was conducted five times at intervals of a week, and DI, CI, OHI, and P.H.P. index were recorded. As a result, the test dentifrice containing Dextranase was found effective and a statistically significant difference was observed in contrast to the control dentifrice. Moreover, it was confirmed that a continual use over the period of one month did not resulted in oral anomaly either subjectively nor objectively.
Then, 115 healthy adult women were seleted and divided into two groups. The same two kinds of dentifrice as used in the first experiment for effectiveness, one containing Dextranase and the other not were used in this second experiment again. Subjective and objective conditions of all subjects were observed after three hours of use of dentifrice.
One week late, two groups were crossed each other, and the previous test group used a control dentifrice, and the previous control group a test dentifrice. In the same way, an examination was done after three hours of use of dentifrice.
Consequently, abnormal conditions such as oral pain, oral ill feelings, or oral stripping were not observed.
Therefore, a dentifrice containing Dextranase was found effective in plaque removal and caries prevention.

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It has been reported that a bacteriolytic enzyme derived from Streptomyces globisporus strain 1829 (SG enzyme) possessed strong lytic action against the cariogenic bacteria and dental plaque.
The pur pose of this study was to determine whether the adsorption and elution of the enzyme in powdered human and bovine enamel and hydroxyapatite could be detected.
The bacteriolytic enzyme was successfully absorbed into the powdered enamel and hydroxyapatite in 0.005 M phosphate buffer, pH 6.8, and approximately 50% of the adsorbed enzyme was eluated in 0.1 M phosphate buffer, pH 6.8. Hydroxyapatite which had been pre-treated with salivary proteins absorbed the SG enzyme to the similar extent as hydroxyatite without pre-treatment. The salivary proteins and SG enzyme were simultaneously eluated from the hydroxyapatite in 0.1 M phosphate buffer, and a synergistic effect of the eluated salivary lysozyme and SG enzyme was observed.
These phenomena suggested that the SG enzyme may play an effective role in dental plaque control in the oral cavity.

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In a dental epidemiological study, it can be greatly beneficial to use a computer system for filing and analyzing dental information accumulated periodically during a prolonged investigation.
The author has designed a computer program for filing the information obtained from dental examinations of school children in Yahiko Village and Maki Town, Niigata Prefecture, during a five-year period.
A system flow chart of the programing in this study is composed of five programs, each of which has its own particular function. Filing systems of the program ought to include the following;
a) accurate recording of clinical examinations.
b) cording of information recorded about each tooth surface, and designing of a punched card format.
c) check and maintenance of date by using a computer system.
d) filing of data in an external memorizing assembly (e. g. magnetic tape).
In this report, the advantages and problems in using a computer system in this field are also discussed.

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Dental calculus contains various trace elements, but a standardized method of detection has not yet been established. The author detected traces Mn, As, Cd, and Hg in calculus by means of radioactivition analysis and conducted a quantitative analysis of them.
The results of the experiments were as follows:
1) In a preliminary experiment, a standard sample and each test sample were irradiated with neutrons under fixed conditions, and quantitative values were measured for each sample. The γ-ray-spectrum of each test sample showed a similar peak point contrased with that of a standard sample of calculus: ⁵⁶Mn had 0.874 Mev of γ-ray spectrum, ⁷⁶As had 0.549 MeV of γ-ray spectum, Cd had ^115mIn 0.335 MeV of γ-ray spectrum, and ²⁰³Hg had 0.274 MeV of γ-ray spectrum.
2) The four regions of Tokyo, Osaka, Toyama and Niigata were compared as to the detection of Mn, As, Cd, and Hg in calculus. A significant difference was found for Mn and Cd between regions. The most Mn was found in the Toyama region, and the most Cd was in the Tokyo region.

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Experiment I; The incidence of Str. mutans in the dental plaque of 20 students was examined. The plaque was obtained from the buco-lingual smooth surface of the lower anterior teeth and the occlusal pits and fissures. Str. mutans could not be detected from the buco-lingual smooth surface of the lower anterior teeth, but it was detected from the occlusal pits and fissures in all subjects.
The ratio of Str. mutans to total Streptococcus was 29.30±27.34 per cent. Experiment II; The incidence of Str. mutans in the dental plaque of 30 patients, ages 19-52, was examined. The plaque was obtained from the buco-lingual smooth surface of the lower anterior teeth, from the approximal surface with a contact point and from the occlusal pits and fissures. The prevalence of Str. mutans in the plaque was 0% (the buco-lingual smooth surface of the lower anteior teeth), 20% (the approximal smooth surfaces with a contact point) and 65% (the occlusal pits and fissures).
The ratio of Str. mutans to total Streptococcus in the plaque of the occlusal pits and fissures, was about eight times that of the approximal surfaces.

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