To understand the pathology of caries lesions, it is important that the earliest stage of destruction in the surface layer of enamel and also the point of attack at the superficial layer of the enamel should be directly demonstrated. For this reason the progress of destruction in caries-like lesions produced on thin sections of teeth should be successively followed up.
While histopathological evidence on incipient caries lesions has been accumulated by numerous researchers, little has been published concerning a direct demonstration of structural changes.
This paper, then, deals with a successful new method for continuous observation of changes in lesions produced on ground thin sections of teeth under the microscope. Plano-parallel thin sections of approximately 20μ in thickness were prepared from undecalcified teeth according to procedures previously published. The sections were cemented with 3% toluene solution of polyvinylmethylether between two pieces of glass, leaving intact only the small area of the enamel surface to be observed (Fig. 1).
The area thus prepared was exposed to the attack solution running at a constant flow rate through the apparatus assembling on the microscope as shown in Fig. 2 and 3.
The changes were observed and recorded by microscopic photography for long periods of time. In particular, 16 mm. cine-automatic photography was most useful in following details of the changes.
As can be seen in Fig. 4, in which changes on the enamel section produced by N/10 acetic acid buffered to pH 5.0 were sucessively shown for 67 hours according to the method described here, the reliability and availability of this method was confirmed. The method will be helpful for getting further information on the pathology of enamel caries.

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A study was made of 12 male adults from 20 to 28 years who brushed the facial and lingual surfaces of their upper and lower anterior and posterior teeth using three kinds of manual toothbrushes, which differed in the shape of the shank, the number of tuft, and stiffness, but were the same in the brushing plane (straight).
The three kinds were the Rolling type toothbrush (tufts are of a multitufted design and stiffness in medium), the Straight type toothbrush (tufts are of a tufted design and soft texture), and the Banet type toothbrush (the handle has a curved oval concave in the shank in the direction of the brushing plane and is at an angle of 10° with respect to the brushing plane or head, tufts are of a multitufted design and stiffness is medium). The adults followed their habitual brushing method for 20 seconds in each area.
Quantitative determinations were made of brushing force, brushing strokes per 20 seconds and percent of debris removal.
(debris index before brushing minus debris index after brushing/debris index before brushing times 100%)
The debris removal for each toothbrushing area and each toothbrush was discussed on the basis of relaticns between brushing force and the number of brushing strokes, and between the percent of debris removal and the product of brushing force times the number of brushing strokes.
Brushing force was generally 200-1, 000 g and the number of brushing strokes was 30-100 per 20 seconds.
Variations in brushing force and the number of brushing strokes were due more to individualities than to toothbrushes and brushing areas.
The above findings meant that habits appeared with individualities in brushing procedures. Brushing force and the number of brushing strokes were inversely proportional among adults who showed a 100 percent debris removal, but were not necessarily so among the examinees whose debris removal was less than 100 percent.
The percent of debris removal was generally proportional to the product of brushing force times the number of brushing strokes except in the labial surface area of the upper and lower anterior teeth and the lingual surface area of the upper and lower right posterior teeth. The percent of debris removal was higher in the former area and less in the latter area than in the other areas.
Those findings seem to indicate that the difficulty or easiness of brushing procedures was reflected on the brushing areas.
The brushing areas did not always show the same percent of debris removal depending upon the kind of toothbrush used. A Banet type toothbrush was most effective for the facial surfaces of the upper anterior and posterior teeth as was the case with a Straight type toothbrush in brushing the lingual surfaces of the upper and lower anterior teeth.
The present experimental data revealed that the percent of debris removal was better evaluated by the product of brushing force times the number of brushing strokes than by brushing force only.

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A study was made of 33 primary school pupils who brushed the labial surfaces of their upper anterior and posterior teeth using three kinds of manual toothbrushes different in the shape of the shank, the number of tufts and stiffness but the same in brushing plane (straight) and tufts (tufted design).
The three kinds were the Rolling type toothbrush for pupils (stiffness is medium), Wakaba No. 1 toothbrush (stiffness is medium), and Wakaba No. 2 toothbrush (soft). The pupils followed their habitual brushing method for 20 seconds in each area.
Quantitative determination were made of brushing force, brushing strokes per 20 seconds and percent of debris removal
(debris index before brushing minus debris index after brushing/debris index before brushing times 100%)
The debris removal effect due to the toothbrushing areas and toothbrushes was discussed on the basis of the relations between brushing force and the number of brushing strokes, and between the percent of debris removal and the product of brushing force times the number of brushing strokes.
Brushing force in the pupils was 100-500g, which was less than in adults. The range of the number of strokes was 30-100 strokes per 20 seconds, which was the same as in adults.
Differences in brushing force among the brushing areas were observed in adults, but not in the pupils.
Habits in the pupils did not reflect individualities in brushing procedures as much as in adults.
Some pupils (Fig. 2, Subjects A-G) showed more removal effect with a stiff toothbrush than with a soft toothbrush, while others (Subject O) showed the opposite result or similar data (Subjects L-N), that is, debris removal was related to not only brushing force but also to the number of brushing strokes.
Brushing force and the number of strokes were inversely proportional among subjects who showed 100 percent debris removal, but were not necessarily so among pupils whose percent of debris removal was less than 100.
The percent of debris removal was generally proportional to the product of brushing force times the number of brushing strokes.
There was no difference in debris removal between adults and the pupils in brushing the labial surface of the upper teeth, which was easy to brush regardless of the skill of brushing procedures among the examinees of different ages.

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Since atomic absorption spectrophotometry was introduced for the determination of magnesium in blood serum by Willis in 1960, many studies have been published on the use of the method for determination of trace metals in biological materials. However, reports on trace heavy metals in teeth are scarce. Much more analytical data are necessary.
The present report describes a method for using atomic absorption spectrophotometry for the determination of trace heavy metals (lead, copper, cadmium and zinc) in extracted human permanent teeth.
(1) A tooth was dissolved in 5 ml of nitric acid, and then dried and ashed by heating in a silica crucible for 10 hr in a muffle furnace at 400-450°C. The ash was dissolved by gentle warming in 5ml of hydrochloric acid and transferred to a 20 ml volumetric flask. Distilled water was added to make 20ml of sample solution.
(2) Mixed working standard solutions were used for the determination of lead, copper and cadmium.
(3) Lead, copper and cadmium were chelated by 3ml of 1% ammonium pyrrolidine dithiocarbamate (APDC) and extracted simultaneously with 5 ml of methyl isobutyl ketone (MIBK) from 10 ml of the sample solution at pH 3.5. Zinc was determined directly in diluted water solutions.
(4) Interferences of calcium in measurements were investigated. Calcium interferences were compensated by the addition of citric acid both to the working standards and sample solutions, and also by addition of calcium to the working standard solutions.
(5) Detection limits were approximately 0.7 μg Pb, 0.3 μg Cu and 0.03μg Cd in a final volume of 20ml, equivalent to one whole tooth.

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The glucose metabolism of streptococcus mutans and streptococcus sanguis was examined anaerobically in a buffer containing NaHCO₃+KH₂PO₄.
Streptococcus mutans produced more acetic acid and formic acid in a buffer without KH₂PO₄than in a buffer containing KH₂PO₄.
Production of lactic acid by str. sanguis increases with increasing KH₂PO₄ concentration.
The oxygen uptake of these streptococci in hydroxyl-apatite and in enamel powder was examined. Oxygen uptake was almost nil when str. mutans was grown in B.H.I. broth, but it increased considerably when the culture medium was B.H.I. broth+5% sucrose. Str. sanguis did not show this variation.

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The relationship between oral cleanliness and the prevalence of dental caries and gingivitis were investigated in 288 school children of 12 to 15 years residing in the suburbs of Sendai in 1969 and in 265 similar children in 1970.
The scores of the Simplified Oral Hygiene Index (Greene, J.C. and Vermillion, J.R. 1964.), PMA index of front teeth (Schour, I. and Massler, M., 1948) and DMFT index were treated statistically and the following results were obtained. A close correlation between the scores of OHI-S and PMA of front teeth was present but no correlation between OHI-S and DMFT as several investigators had reported.
In the study of 1970, the subjects were rated by Occlusal Plaque Index (O·P·I·), estimated by the amounts of the disclosed occlusal plaque of the four first molars. The O·P·I· scores were closely correlated with DMFT index scores, and the coefficients of correlation were 0.371 (P<0.001) in 134 boys and 0.248 (P<0.01) in 131 girls.
As a highly statistical significant relationship was found between the amounts of the occlusal plaque of molars and the prevalence of dental caries, the Occlusal Plaque Index could be a useful index for estimating the status of oral hygiene in public.

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Quantitative studies on Candida in healthy oral cavities were carried out. A new method was designed which enables more candida to be collected than before.
1. Detection of Candida in the oral cavity: Successive inspection for 10 days was done on 10 patients. In 4 cases it was detected in gargle and centrifugal sediment; in 2 cases it was detected in the sediment only; in 4 cases it was undetectable in either material.
Daily fluctuation of the candida count was not found. The candida count in gargle showed a normal distribution. The count was highest on the surface of tongue.
2. Relation between candida and lactobacillus counts: A positive correlation was shown between those in gargle and on the surface of tongue.
3. Influence of antibiotics on the counts of candida and lactobacillus and on candidiasis: Administration of antibiotics under the same conditions resulted in a distinct difference between 2 groups-detectable and undetectable before antibiotics administration.
The most increased count was of C. albicans and this increase was strongly related to the appearence of candidiasis.
The significance of candida detection in the oral cavity before antibiotic administration was discussed.

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