In a previous study we demonstrated that the cells of nonadhering Streptococcus mutans AHT mutants and Escherichia coliand the inert resin particles adhere to glass when incubated with extracellular glucosyltransferase (GTF) from S. mutans AHT and sucrose. The results prompted us to examine whether oral inhabitants other than S. mutans can induce plaque formation and subsequent development of dental caries in rodents by providing them with sucrose-containing diet and cellfree GTF soultion.
The cells of Lactobacillus casei PSR 3002 and indigenous flora in the plaque collected from the molars of golden hamsters adhered to glass when incubated with sucrose and cell-free GTF from S. mutans AHT-SMRI. However, L. casei did not establish itself in the mouth of penicillin-pretreated SD rats reared on cariogenic diet # 2000 and cell-free GTF solution. Consequently, no carious lesions developed on the molars of the rodents. The oral administration of GTF as a drinking fluid neither significantly induced microbial plaque formation nor caries development in the sucrose-fed golden hamsters harbouring indigenous lactobacilli. In this case, however, the extent of plaque formation and caries development of the GTFadministered animals was higher than those of the control animals provided with distilled water.
No decisive conclusion can be drawn from these results. There still remains a possibility that tenacious glucans produced by extracellular GTF of S. mutans could induce non-specific adherence of oral bacteria and thus that they are involved in the formation of microbial deposits and subsequent development of carious lesions on teeth. A decisive conclusion must await further study.

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Dental caries is known as a disease of very high morbidity. In order to protect of dental caries, fluoride has been broadly used. This study deals with the effect of the rare earth element lanthanum in controlling dental caries. There are very few instances of application of lanthanum in dental study and practice. However, considering the fact that it is of low toxity and is used as a hardening reagent for glass, lanthanum could have hardening effects of dental enamel.
As a preliminary study of the cariostatic effects of lanthanum, we examined its MIC for Str. mutans, its acute toxity in mice, and the inhibition of experimental caries in hamsters, using a water solution of Lanthanum nitrate.
The result was as follows.
1) The MIC of Lanthanum nitrate for Str. mutans was about 2000μg/ml.
2) The LD₅₀ of Lanthanum nitrate for mice was about 150mg/kg.
3) Lanthanum at a concentration below 3μg/ml obviously reduced experimental caries produced by Str. mutans 1089 in hamsters.
4) Very little inhibitory effect of Lanthanum nitrate on alveolar bone loss was observed.

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Although the lierature contains many reports concerning the prevalence of dental caries in Japan, there is little information about the relationship between dental caries in preschool children and dental care by their mothers.
Seven hundred and twenty-one children between the ages of 3 and 5 years were examined by three dentists. A mouth mirror and dental explorer were used to detect lesions. Questionnaires were given to thetr mothers concerning toothbrushing, between-meal eating and topical application of fluoride for children. The prevalence rates of clinical caries ranged from 90.4% for 3-year-olds to 97.5% for 5-year-olds. The mean number of decayed teeth was 7.5, 8.8 and 10.2 for 3-, 4- and 5-year-olds children, respectively. In statistic analysis, the group taking one between-meal snack a day showed a lower mean number of decayed teeth than another group (p<0.001) taking 2 or 3 between-meal snacks a day. The children who were reported eating“sweet”and/or“sticky”between-meal items exhibited a high def (decayed, indicated for extraction and filling deciduous teeth) rate (p<0.001, x²-test). Also in those children who consumed snacks at bed time there was a greater incremental caries score (p<0.001, x²-test). In the group brushing more than twice a day, their toothbrushing was usually checked by the mothers and there was low caries frequency. This study confirmed that frequency, items and time of between-meal eating and tooth brushing might play an important role in preventing dental caries in preschool children.

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For an enamel solubility test as screening procedure of caries susceptibility (activity), the follwing five conditions are required : Ideally, the test should be, (1) applicable to all tooth enamel surfaces, (2) easy to perform, (3) simple in analysing its result (4) minimum in damaging the enamel, and (5) known about its accuracy.
The present study was performed to find a method with above five conditions. The following results were obtained.
1) Sensitivity of calcium by atomic absorption spectrophotometry (AAS) was 0.05 (1% absorbance value) μg/ml of 0.005 (2N=S value) μg/ml.
2) The linear range of phosphorus standard curve by AAS of molybdenum was 0.3-0.5μg/ (n-butyl acetate) 5 ml (Air-Acet. flame) and 0.1-1.0 μg/ (n-butyl acetate) 5 ml (Nitrous-Acet. flame).
3) The determination of calcium by AAS was interfered with the presence of sodium fluoride, EDTA, albumin and phosphate. Such interference was overcome when 3 mg/ml of lanthanum was added to the sample.
4) The amounts of calcium and phosphorus obtained from the enamel surface by a filter paper disc containing perchloric acid changed with volume, concentration and application time of the perchloric acid, and pretreated condition of the enamel surface by various polishings. It was also found that calcium/phosphorus ratio changed similarly.
5) Scanning electronmicroscopy showed that the amount of dissolved enamel correlated with the roughness of the etched enamel surface.
6) When a filter paper disc and a cellulose acetate membrane disc were compared with each other, the cellulose acetate membrane disc was found to be more suitable as an applicating material than the filter paper disc, since the latter contained a small amount of calcium.
7) The amounts of calcium, dissolved from enamel surfaces after application of the sixteen agents, were investigated. Acid buffers (pH 4.0 sodium acetate-acetic acid and others) showed a highest amount of calcium dissolution, organic acids (acetic acid, lactic acid, tartaric acid and others) an intermediate, and inorganic acids (hydrochlyric acid and perchloric acid) alowest.
8) When the dissolution of calcium was less than 3-4 μg, the enamel surface was still intact macroscopically.
9) It was concluded from the present study that the method for enamel solubility, that is, application of a cellulose acetate membrane disc (∅3 mm) with the acid on the enamel surface and then measurement of calcium in the disc by AAS, satisfied three (1, 2 and 3) of the five conditions mentioned above.

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The author reported in a previous paper that the method for enamel solubility (application of a cellulose acetate membrane disc (φ3mm) with the acid on the enamel surface and then measurement of calcium in the disc by atomic absorption spectrophotometry) had a great merit as an enamel biopsy.
This article reports on the selection of the acid agent by studying both variation of the calcium dissolution and morphological changes of the enamel surface after acid agent application.
1) Three acids (acetic acid, lactic acid and perchloric acid) and three buffers (sodium acetate-hydrochloric acid buffer, sodium lactate-lactic acid buffer and sodium acetate-acetic acid buffer) were studied about their enamel solubilities. Mean enamel solubility of a single tooth was determined from calcium amounts of the different locations on the buccal or labial tooth surface. Acid etched enamel surfaces were studied macroscopically and scanning electronmicroscopically. In addition, some of the surfaces were exposed to synthetic saliva for six days and then observed similarly.
2) The mean enamel solubility showed a reverse relationship with the coefficient of variation, although the latter became plateau when the amount of dissolved calcium was more than 0.3-0.4 μg. The relationship may be expressed in the following fomula;
y=ax^-bx: the calcium amount dissolved (μg)
y: the coefficient of variation
a; b: the constant of the each acid
3) Coefficient of variation became plateau, when the dissolved calcium amounts of unerupted upper first premolar and erupted upper first premolar became 0.4-1.0 μg and when that of erupted lower central incisor became 0.3-0.4 μg.
4) The macroscpic and scanning electronmicroscopic changes of the enamel surface appeared for the first time in the erupted upper first incisor at 1.5-2.0 μg of dissolved calcium amount, in the erupted upper first premolar at 1.5-2.0μg and in the unerupted upper first premolar at 0.5μg.
5) When both erupted and unerupted teeth with etched enamel surfaces were exposed to synthetic saliva for six days, the etched enamel surfaces of erupted teeth did not show any changes scanning electronmicroscopically, but the etched surfaces of unerupted teeth revealed somewhate minute changes.
6) Calcium amount dissolved by pH 2.3 sodium acetate-hydrochloric acid buffer was within 0.4-1.5 μg range in coefficient of variation plateau, and above this range, the changes of the enamel surface were recognized macroscopically and scanning electronmicroscopically.
7) It was concluded from the present study that the method for enamel solubility, namely application of a cellulose acetate membrane disc (φ3mm) with pH 2.3 sodium acetate-hydrochloric acid buffer 2μl on the enamel surface and then measurement of calcium in the disc by atomic absorption spectrophotometry, had a significant merit as an enamel biopsy.

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1) The present study was undertaken to examine a relationship between the enamel solubility and the fluoride concentration in the surface enamel. Four succesive layers of the enamel of extracted human and bovine teeth were etched off by 0.5 M perchloric acid 2μl from the distal location of the buccal or labial tooth surface. Fluoride and calcium in each layer were examined by the fluoride ion electrode and the atomic absorption spectrophotometry, respectively. Enamel solubility was determined by measuring the amount of calcium in pH 2.3 sodium acetate-hydrochloric acid buffer dissolved from the mesial location of the same surface.
2) The following fomula of the fluoride gradient concentration of the surface enamel was obtained from the above results:
y=ax^-b x: the depth (μm)
y: the fluoride concentration (ppm)
a; b: the constant of the examined surface enamel
Using this equation, the comparison of the fluoride content between the samples was made.
3) Enamel fluoride in the extracted tooth samples was as follows.
Sample
Fluoride concentration at 0.8 μm depth
(mean±SE)
human erupted upper central incisor 444±115 (ppm)
human unerupted lower first premolar 267±87
bovin erupted lower incisor 222±52
4) APF solution treatment increased the fluoride concentration in the surface enamel of all teeth. Among teeth the human unerupted lower first premolar showed a most remarkable increase in fluoride concentration.
5) The enamel solubility (mean and standard error of dissolved calcium amounts) was 3.11±0.5μg in the bovin lower incisor, 0.27±0.002μg in the human lower premolar, and 0.28±0.02μg in the human upper central incisor.
6) There was a reverse relationship between fluoride concentration and enamel solubility in the surface enamel.

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In an effort to evaluate the dental health situation of elementary school children as correlated to the first molars in the routine school physical examination, a fairly high correlation was found not only between the individuals but also between different elementary schools.
From these findings, it was concluded that the entire dental health of a proup of children could be assumed from the findings of their first molars.

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Effects of surface active agents, sodium N-lauroyl sarcosinate (SLSa) and sodium lauryl sulfate (SLSu), on the bacteriolytic activity of the enzyme derived from Streptomyces globisporus 1829 were sudied.
Resting whole cells or crude dl walls of Streptococcus mutansBHT were allowed to react with the lytic enzyme in the presence or absence of the surfactants. After appropriate time of incubation at 37°C, bacterial lysis was determined by monitoring the turbidity of the suspensions and the amounts of free reducing sugars released.
Lytic activity of the enzyme was enhanced by the presence of SLSa at concentrations higher than 0.3% when the whole cells were used as a substrate, and at a concentration even as low as 0.1% when using cell walls. On the other hand, lysis of whole cells by the enzyme was increased by the presence of SLSu at concentrations ranging from 0.03 to 0.12%, but the enhancing effect of the surfactants at those concentrations could not be demonstrated when using cell walls as substrate. At concentrations higher than 0.15%, SLSu markedly inhibited the enzymatic lysis of both whole cells and cell walls. These results were consistently demonstratred by using both of the two methods to monitor bacterial lysis. Apparent reduction in turbidity of substrate suspensions caused by SLSa or SLSu alone did not accompany significant release of free reducing sugars, and vice versa.
These results suggest that SLSa and SLSu increased the bacteriolytic activity of the enzyme by different mechanisms.

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