The plaque control has been discussd and practiced in many ways recently. We divided these ways into four categories and picked up four factors which were considered to be the most basic and important in clinical plaque control.
To study about the correlation between these factors, sixty-three adult women were examined in regard to toothbrushing and the plaque index was evaluated. According to clinical tests, following results were obtained.
The plaque control effects of three toothbrushing methods, i. e., Rolling, Scrubbing and Bass' methods, were not statistically significant differences. However, the two-factor interaction between factors of toothbrushing methods and surfaces of teeth was statistically significant and the order of plaque control effects on lingual and palatinal surfaces was Scrubbing>Rolling≥Bass' methods.
With respect to the factor of the hardness of the tooth-brush hair, it had a statistically significant effect on the plaque control. In proportion to the hardness, the order of plaque control effects was Hard>Medium≥Soft. These effects were not influenced by any other factors and had no statistically significant interaction.
As for the dentition and surfaces of teeth, plague control was more difficult on the lingual and palatinal surfaces under the conditions used in these clinical tests. Moreover, on lingual and palatinal surfaces Scrubbing method had a relatively stronger plaque control effect.
In this study, the cumulative analysis of variance of multiple-way classification was applied to confirm the interaction of factors. The results suggested that this statistic analysis was very useful for examining the interaction and considering the change of factors in the clinical tests.

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There is a fairly large body of literature concerning the influence of bodily growth and environmental factors on the eruption of teeth in man. However, studies dealing with tne correlation detween the number of erupted deciduous teeth and the value of bodily growth are comparatively scanty. In the present work. I studied the correlative coefficients of the stature, weight, weight ratio, and increasing rates of both stature and weight in an effort to elucidate the relationship between these body factors and deciduous tooth eruption. By way of study materials, a selective use was made of 5, 119 boy and girl infants of 5 to 18 postnatal months, who were reared in more or less the same family circumstances. At the same time, observations were made of differences, if any, between the firstborns and second-borns. As a result of the study. I arrived at the following conclusions:
1. Stature, weight, and their increasing rates. In these categories, boys showed a tendency to be larger than girls in corresponeding postnatal months. The difference became statistically significant after 8 postnatal months. In terms of stature, there was a tendency for the firstborns to be somewhat larger in both boys and girls. 2. Weight ratio. Boys showed a tendency to be laerger than girls in corresponding postnatal months. The first-born group also tended to be laerger. 3. In the number of erupted deciduous teeth, boys showed a larger count than girls after 10 postnatal months. The first-born group showed a larger number of erupted deciuous teeth than the second-born group. 4. In the correlation fetween the number of erupted deciduous teeth and stature and weight, the correlative coefficients became larger in proportion to the postnatal months, but statistical difference was absent in every group. An absence of statistical difference was also seen between the first-born and second-born groups. 5. In the Number of erupted deciduous teeth and increasing rates of stature and weight, boys and girls gave a significant correlation after 6 postnatal months. There was no significant difference between the first-born and second-born groups in either sex. 6. In the correlation between the number of erupted decidous teeth and the increasing rates of stature and weight, the increasing rate of stature was most closely related, followed by the present stature, increasing rate of weight, and present weight in descending order. Therefore, I conclude that there exists a close relationship between the deciduous teeth eruption and the amount of physical growth of infants.

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It has been reported by various investigators that a greater proportion of the contamination on the part of dentists and their clinics is due to drilling with high-speed air-turbine handpieces. It is not only the dentist or his clinic that is contaminated, but also the handpieces themselves that probably become contaminated. For this reason, some kind of countermeasure is needed. But, because of their structure it is difficult to disinfect these instruments and, therefore, we must search for an easy method of disinfection in clinical environments.
In the belief that ultraviolet ray, if it could be proved sufficiently effective for bacteriocidal purposes, would provide one easy means of disinfection, I carried out the following research. For study purposes, 3 different types of dental clinics were selected:
1) those clinics where handpieces were not disinfected at all dnring dental treatment, 2) those clinics where handpieces were occasionally disinfected, and 3) those clinics where handpieces were disinfected every time they were employed.
In these 3 different types of dental clinics, efforts were made to wipe off the handpieces for 5 days prior to the treatment in the first week and at the end of treatment daily in the second week.
The number of bacterial coloneis between these two-week intervals were measured and analyzed.
By way of determining the disinfecting effects of ultraviolet ray on different bacteria, Escherichia coli, Staphylococcus aureus and Bacillus subtilis were selectivly used to establish the density of ultraviolet ray and the time of bacteriocidal effect.
In the last phase of the study, an apparatus was devised so that the entire surface of handpieces could be disinfected and the different bacteriocidal effects were comparatively examined.
As a result of the present sudy, I arrived at the following salient conclusions.
1. In dental clinics where handpieces were not routinely disinfected, the degree of bacterial infection was much larger than in other dental clincis where handpieces were regularly disinfected.
2. Even in dental clinics in which handpieces were disinfected after every dental treatment, they were not always free from bacterial infection.
3. The time required for disinfection of Escherichia coli, Staphylococcus aurens, and Bacillus subtilis by an application of ultraviolet ray could be much reduced by increasing the intensity of the ultraviolet ray.
4. The bacteriocidal effects of ultraviolet ray were most prominently observed with Escherichia coli, followed by Staphylococcus aurens, and Bacillus subtilis.
5. An ultraviolet disinfecting apparatus, devised by me for this study, was effective in killing the bacteria on handpieces within 5 minutes.

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In general, dextranase is an effective plaque control agent which enzymatically resolves and removes dental plaque.
In this study, the effect on plaque control of dextranase prepared from chaetomium gracile and added to a dentifrice was examined in clinical tests.
Sixty-two male subjects aged about thirty to fifty and employed in a factory, were divided into two groups. Each group used a test dentifrice containing 2000 units of dextranase per grain and a placebo dentifrice without dextranase for one month. Then the OHI was evaluated.
Regarding the debris-index, reduction rates of the test and the placebo dentifrice groups were 62.3 and 34.4%, respectively, and a statistically significant difference (P<0.01) was observed between them.
On the other hand, in the calculus-index, reduction rates of the test and the placebo dentifrice groups were 76.5 and 74.9% respectively. Their effects were almost the same and there was no statistically significant difference.
These results suggested that an effect on plaque control of dextranase could be expected in clinical use, but that it would have on effect on the reduction of calculus.

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The purpose of this study was to examine the regional and age-related variations in the enamel solubility and the fluoride concentration on the surface of women's lower first premolars and to develop a technique to determine both enamel solubility and fluoride concentration using dissolved enamel from the same point on the tooth surface.
The following results were obtained.
1) Both the enamel solubility and the fluoride concentration could to be determined at the same window of enamel (3-mm diameter) on tooth surface.
2) Fluoride concentration on the approximal surfaces were higher in older persons than in younger persons. The fluoride concentrations on the buccal surface increased transiently after eruption and then decreased. The decrease of fluoride concentration appeared to be most remarkable near the biting edge of the buccal surface in earlier stage.
3) The differences in the fluoride concentrations between the approximal surfaces and the buccal surface in the group of unerupted teeth were not significant, but in the older group the approximal surface showed significantly higher fluoride concentrations than the buccal surface.
4) The gourp of unerupted teeth showed significantly lower fluoride concentrations than the: group of erupted teeth, and the most scattered value of all.
5) Enamel solubility tended to decrease first and then to drop to a plateau shortly after eruption.
6) There were no differences in the enamel solubility between the approximal surfaces and the buccal susface, but in the older group the approximal surface. showed lower enamel solubility than the buccal surface.
7) The group of unerupted teeth showed the least scattered values of all in the enamel solubility. The enamel solubility of the approximal surfaces tended to be more dispersed than that of the buccal surface.
8) There was a reverse relationship between fluoride concentration and enamel solubility.

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The hemagglutinin (HA) of S. sanguis ATCC 10557 was apparently present on the cell surfaces and released by the treatment with freezing and thawing. An affinity chromatography on D-galactose binding-Bio-Gel P-2 was significantly effective in purifying the HA.

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The effect of fluoride mouth-rinsing solution on human enamel was examined by means of electron probe microanalysis and X-ray diffraction. Experiments were made in vitro by applications of phosphoric acid-acidified NaF solution (500 ppm of F^-; pH 5.0) to the intact enamel.
The distribution of fluorine, calcium and phosphorus in enamel following the topical fluoride treatment (30 minutes every day for 8 weeks) were demonstrated by electron probe microanalysis.
X-ray diffractometry was performed by the use of X-ray microfocus diffraction. Reaction roducts and crystallinity of the enamel were observed in the X-ray diffraction pattern obtained with a microphotometer. The variation of crystallinity was estimated from the half-maximum breadth values (310), (002) reflections of enamel apatite.
Electron probe microanalysis shows that the fluorine concentration of surface enamel was increased not only on flat surfaces but also in fissure areas by the repeated use of fluoride mouthrinsing solution. Espeiaclly high concentration of fluorine was observed at the subsurface decalcified area of the enamel surface.
In the X-ray diffraction experiments, no reaction product was detected. The crystallinity of enamel apatite of the surface layer was increased in both a- and c-axis directions by application of fluoride mouth-rinsing solution. In the inner layer it seemed that the crystallinity of enamel apatite in the a-axis was also increased by the use of fluoride mouth rinse.

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The fluoride acquisition in vitro by intact enamel from phosphoric acid-acidified NaF solution (500 ppm of F^-; PH 5.0) and the acid solubility of the enamel were examined. Specimens were treated with fluoride mouth-rinsing solution for 30 minutes every day at 37°C during 8 weeks and immersed in artificial saliva.
The fluoride content in succesive layers of enamel was determined by using an ORION ion meter (model 801) and fluoride electrodes. The calcium content was determined by Yanagisawa's method using Plasmo Corinth B.
An acid solubility test was made to determine the released calcium content from enamel into a 0.4 M acetate-sodium acetate buffer (pH 4.0) during three hours every thirty minutes.
In the experiments of fluoride mouth-rinsing, the fluoride acquisition by intact enamel was increased. Especially the surface layer of enamel contained greater amounts of fluoride, which increased with time. The distribution of fluoride was observed in the inner layer of enamel treated with fluoride mouth-rinsing solution. An acid solubility test proved that the acid resistance was increased 2-3 times more in the fluoride treated enamel than in the control.

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