A new simple techique for the microdetermination of fluorine in the presence of aluminum was obtained by using the fluoride ion electrode. Procedures are as follows ;
Aluminum fluoride complexes were deeomosed in alkali (pH>12) and the liberated aluminum was masked with oxine. The pH and total ionic strength were adjusted with TISAB, and fluorine determination was carried out with no extraction of the aluminum-oxine complex and free oxine.
The calibration curve showed a linearity down to less than 0.1 ppm (5.3×1O^-6M) of fluorine in the presence of 4 ppm of aluminum and oxine, which is as good as measurements obtained in the absence of aluminum.
Recovery of 1 ppm of fluorine was relatively good-about 95%-, even in the presence of 200 ppm of aluminum. Good recovery of fluorine added to artificial cryolite was also found.

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Orion solid-state electrodes for heavy metal ions such as for cadmium, lead, silver, and cupric ions were evaluated regarding their limits of detection, effects of pH, in- terferences by other ions, and applications to urine analyses.
The authors are convinced that these electrodes precisely detect low levels of each corresponding ions without notable interference by pH or other ions, and that urine analyses may be possible by the use of adequate masking agents for interfering ions through the Known Addition Method.

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It is well known that the atomic absorption method of analysis is suitable for the simple or rapid determination of traces of metals such as zinc, lead, copper or cadmium in biological materials. In this ex- periment, the method was applied to the analysis of cadmium, zinc and lead in human teeth.
An appropriate weight of teeth was digested according to the wet ashing process with nitric acid and hydrogen peroxide. After adjustment to pH 3.0 by the addition of aqueous ammonia, the solution was brought up to 25 ml. To this solution was added 5 ml of a 3 percent aqueous solution of ammonium pyrrolidine dithiocarbamate and 10 ml of methyl isabutyl ketane.
The mixture was shaken, and after the layers were separated, the solvent layer was centrifuged at 3000 rpm for 5 minutes. The cadmium and lead content were directly analysed, and for the determination of zinc an aliquot of the solvent was diluted to 100 times its volume.
Judging from the consistency of the results obtained by the standard addition method and the completeness of the recoveries, the method is reliable and free from interference.

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It has been suggested that deciduous teeth could be useful material for the analysis of the minerals available to the human body during the time the teeth are formed. In this study, an attempt was made to define the variation in the cadmium, zinc and lead content of the various types of deciduous teeth collected from two dif- ferent areas (Tokyo and Toyama city) in Japan. It was also of interest to determine the effect of breast feeding versus bottle feeding.
Therefore the pooled teeth were classified as to the residence area, the type of teeth and the length of time the child was fed by breast or bottle. The cadmium, zinc and lead values of teeth were obtained by analyzing 795 deciduous teeth by atomic-absorption spectrophotometry. Calcium determinations were made according to the ethylendiaminetetraacetic acid (EDTA) titration method.
The results obtained are summarized below.
(1) While the distribution patterns of calcium and cadmium were slightly logarithmic-normal, those of zinc and lead were shown to be normal.
(2) There were no appreciable differences in the mean concentrations of the three metals between Tokya and Toyama city, and no significant differences were found between the kinds of diet
(3) In comparisions between various types of teeth, the mean concentrations of three metals were found to be low in the following descending order: incisors, cuspids, and molars.

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This study was made to investigate the connection between interdental space and interproximal caries in the deciduous teeth by means of “neighboring age” as defined by the author. The materials were the same infants and children of 0, 1, and 2 years of age in 1965 in Kameoka City, Kyoto, on which the “Studies on Epidemiological Patterns of Caries Attack in Deciduous Teeth” had been made by means of cohort survey by the author.
Interdental spaces were examined at the semiannual oral examinations by inserting a wire (diameter: 0.5mm) between two contiguous teeth and noting “Space” where the wire passed and “Contact” where it did not.
Neighboring age: Considering that the neighboring relationship is formed between two tooth surfaces by the eruption of a tooth next to an existing tooth, the neighboring age was counted from this point and by half years. Furthermore, because the neighboring relationship may change as time elapses, the calculation was made only with the tooth surfaces which remained spaced or in contact according to the basis shown in Table 1. The numbers of the “contact” and “space” tooth surfaces were as shown in Table 2.
Table 3 shows the caries indexes of the “Contact” group and the “Space” group: that is, caries incidence rate of tooth surfaces during a half year (M_x), number of tooth surfaces newly attacked by caries per initial healthy 1, 000 surfaces during a half year (C_x), and cumulative number of carious tooth surfaces per initial healthy 1, 000 tooth surfaces (ΣC_x).
The polygonal lines of C_x are shown in Fig. 1, and the trend-lines of C_x, ΣC_x, and e^-kx line of the proximal surfaces of Contact and Space groups obtained from Table 3 are as shown in Fig. 2.
Table 4 shows the angle formed by the e^-kx line and the 1-line, and the neighboring age at which the C_x trend-line reached the summit, and ΣC_2.5.
The trend-lines of ΣC_x of proximal surfaces of the opposing tooth in the case of the spaced condition is seen in Fig. 3, while Fig. 4 shows the ΣC_x trend-lines of caries in the opposing proximal surfaces in the contact condition. Of these the trend lines of almost simultaneously erupted pairs of teeth, such as A-B, C-D, A-B, and C-D are almost identical. On the other hand, in the case of D-E and D-E, if one of the pair, that is, D or D, eru- pts about a year before the other, there would be affected cases before any neighboring relationship comes to exist, and D, therefore, shows higher rates than E at 0 year of neighboring age. At 3 years of neighboring age, however, the rates of the two become roughly equivalent. The relation of D and E observed by post-eruptive tooth age in the previous paper exhibited an opposite situation. By either method of counting it is impossible to observe the situation of two teeth that have different eruption times like D-E under the same condition. It was presumed, however, that if they were placed under the same condition the proximal surfaces between D and E would show the same pattern.
Table 5 shows the comparison of Mx between the Contact group and the Space group. It may be of use in the assessment of the effectiveness of floss silk in the prevention of caries.

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It has been proposed that adequate incorporation of fluoride in teeth, particularly in the outer layer of the enamel, increases resistance of teeth to caries.
For this purpose, topical fluoride application and the use of fluoride mouthwashes have been proposed. But no matter how effective, topical application is not destined to gain wide popularity, because this application can be performed only by dentists or dental hygienists and it reguires some dental facilities. On the other hand, the latter, fluoride mouthwashes, is so simple, , rapid and painless that it can be carried out entirely by instructed and supervised public health personnel.
In this epidemiologic study, the effectiveness of fluoride mouthwashes was examined. Male and female schoolchildren of 10 years of age (Numbers of subjects=223) in Osaka, were divided into two groups, experimental and control. Ten ml of acid fluoride-phosphate mouthwash system (500 ppm F^-, pH=5.0) were employed for 30 seconds once a day after lunch at school in the experimental group. In the control group, the condition was the same as the experimental group except that the fluoride solution was replaced with a placebo.
This treatment resulted in caries reduction of 20 to 30% after three years of regular usage. From this result, it was concluded that the fluoride mouthwash can be a useful technique for the control of dental caries on a large scale.

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Antibacterial action of human saliva has beenone of the central subjects in oral biology and numerous studies have been reported. Among the antibacterial factors present in human saliva, the salivary peroxidase has received the most extensive studies. The salivary peroxidase antibacterial system consists of three integral components, that is, salivary peroxidase, hydrogen peroxide and thiocyanate. This antibacterial enzyme is referred to thiocyanate peroxidase. Thiocyanate peroxidase was also observed in the tissue extracts from the salivary glands of the rat, the guinea pig and the cattle.
Although the mode of action of the thiocyanate peroxidase has now been largely clarified, the origin of this enzyme remains obscure.
The purpose of this experiment is to study the origin of this enzyme in the salivary glands of developing mouse with tissue culture technic.
The experimental results are as follows: (1) The activity of thiocyanate peroxidase was detectable at 17 th day in utero in the sub maxillary gland of the mouse, and at the 2 nd day after birth in the parotid gland. There was a progressive increase in the enzyme activity throughout the various stages of perinatal development. This enzyme could not be detected in the sublingual gland of either pre-or postnatal mice. (2) Embryonic submaxillary, sublingual and parotid glands of mice were successfully cultivated using Rose's chamber, and the differentiation and proliferation of glandular tissues were observed for approximately 5 days. The peroxidase in cultivated tissue could be stained by the method of Straus with benzidine. According to the acinar differentiation, the positively stained product in blue which presume secretory granules was developed in secretory cells of the submaxillary gland and parotid gland on the 3rd day after cultivation. However, no positive staining reaction was obtained in the sublingual gland. The possible relation between the positively stained product and the thiocyanate peroxidase is discussed. (3) These findings strongly suggests that the thiocyanate peroxidase develops in the acinar cells of the submaxillary and parotid glands during the perinatal period of the mouse.

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