The purpose of this study is to evaluate the OABC classification, which is divided into 4 classes by the location of dental caries at the dental health examination in infants aged 18 months in Japan, regarding the predictability of caries development in future.
The subjects, 309 infants initially aged 18/19 months, were dentally examined for 22 months, and the relationship between caries increment over the study period and the OABC classes at the age of 18/19 or 24/25 months was analyzed statistically. The following results were obtained.
1) No sex difference in caries prevalence was found. The mean dmft of combined sex groups at the age of 18/19 months, 24/25 months and 40/41 months was 0.54, 2.41 and 9.40, respectively, and the mean dmfs of the same age groups was 0.90, 4.11 and 17.81, respectively, in ascending order.
2) The mean dmft increment over a 22-month period in infants that belonged to each class at 18/19 months of age expanded in the order B, O₁, C, O₂ and A, and the mean dmfs increment over the same period increased in the order O₁, O₂, B, A and C. Therefore, the number of dmf surfaces was more useful than the number of dmf teeth in the comparison of carious increment between the OABC classes.
The three classes of A, B and C at the age of 18/19 months were not enough to evaluate the prediction of caries development for 22 months, because the differences among the caries increments of these classes were small and not statistically significant.
3) The dmfs increment over a 16-month period in infants that belonged to each class at 24/25 months of age increased in the order O₁, O₂, A, B and C, and there were significant differences between every two classes except O₁ and O₂.
Consequently, it seems that the OABC classification is more suitable for 24-month-old infants than for 18-month-old infants.
4) The caries increments over a 22-month period among the infants in 6 new subdivisions (Table 8) in the class 0 at the age of 18/19 months were compared.
The infants with preclinical caries such as white spots had significantly more caries increment than others, so it was thought that the infants with preclinical caries should be differentiated from other subjects. Furthermore, since there were significant differences between D₁ and D₂, and D₁ and D₃ in the infants without preclinical caries, it was supposed that the boundary of debris scores between O₁ and O₂ should be changed to the lower one.
5) A new classification containing 3 divisions, i. e., D₁P·OI), D_2/3P·OII), and D_1/2/3P+ (OIII), in the infants belonging to the class 0 at the age of 18/19 months was proposed. When the mean caries increments over 6 or 22 months periods in these classes were compared, there were statistically significant differences between every two classes except between OI and OII in dmfs increment over 6 months. Therefore, it was suggested that the new classification for 18/19 month-infants was useful and that class of infants with preclinical caries (OIII) was equivalent to class A from the study of individual caries susceptibility over 22 months.
6) When this newly proposed classification was applied to infants at the age of 24/25 months, there was statistically significant difference between OI and OIII in the mean dmfs increment over 16 months, so that this classification seemed to be also suitable for 24-month-old infants.

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Incidence and Progression of Approximal Caries in Deciduous Molars of Preschool Children, Okiuji TAKAGI, Katsuhiko TAURA, Noriko TAKAHASHI and Yoshihiro SHIMADA. Posterior bitewing radiographs of 161 nursery school children in Sendai, initially aged 3 to 4 years in May to July, 1980, were taken every six-months for 2 years to investigate the incidence and progression rate of approximal carious lesions in deciduous molars.
At the initial examination, 1038 caries-free surfaces (X₀), 224 surfaces with carious lesions in the enamel (X₁) and 17 surfaces with dentinal carious lesions up to halfway through the dentine (X₂) were radiographically defined. These were reexamined every 6 months over a 2-year period, and the cumulative progression rate of the X₀, X₁ and X₂ was calculated. The following results were obtained.
1. In the study period, 77.6 % of the X₁ progressed into dentinal caries, and the rest were unchanged. Approximately 34.6 % of the X₁ progressed to possible pulpitis (X₃).
2. In comparing the progression rate between the X₁ of different tooth types, the rate for the mesial surface of the lower first deciduous molars was greater than others.
3. 75.6 % of the X₂ progressed into more advanced involvement.
4. The X₁ had a tendency to progress quickly in the first year, and the X₂ showed this tendency in the second year. The X₀ showed a similar progression rate in both years.
From these results, dentinal carious lesions detected by a bitewing radiograph should be filled immediately, but it is questionable whether radiological lesions defined in the enamel should be treated immediately. Moreover, we think that bitewing radiographs at yearly intervals should be used to define approximal lesions in preschool children, because a relatively large number of carious surfaces are detected by this method.

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We applied the Snyder Test (Simplified S·T MEDIA®) to 351 4-month-olds and 278 18-month-olds. This caries activity test depends on the color change resulting from acid production by oral bacteria in a culture medium containing brom cresol green as the pH indicator.
We evaluated the caries activity by two methods, color comparison with colorimetric tubes and measurement of pH in culture medium by pH meter. But the pH measured by color comparison did not coincide with the pH measured by pH meter in the samples of 114 4-month-olds (33.0%) and 96 18-month-olds (34.5%). We investigated the cause of this.
From several experiments, we found that the presence of Veillonella in the saliva, the use of sticks to collect the saliva, and the ineffectiveness of brom cresol green as the pH indicator in the culture medium were the cause of these misjudged samples.
To counter this, we added a drop of brom cresol green to culture medium at the time of evaluation. Then we were able to get the correct pH of the culture medium easily and evaluate caries activity accurately.

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Temporal changes in caries prevalence rate in 3-year-old Japanese children were examined by employing the Annual Statistics of Dental Health Checkup for 3-year-olds from 1963 to 1983 by prefectures. A high caries prevalence in the primary dentition was clearly noted until the mid-1970s, but no consistent geographic variations were observed. A declining prevalence rate among 3-year-old children has been clearly demonstrated since 1975. A very high caries prevalence rate (over 80%), however, was seen in the Tohoku, Kyushu and Okinawa regions in 1983, which was taken as evidence for geo graphic difference in caries prevalence among 3-year-old children.

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[in Japanese]

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The purpose of this study is to investigate the mechanism by which (NH₄) ₂TiF₆ solution produces its cariostatic effect by means of comparing the artificial caries lesion formation on enamel after treatment with (NH₄) ₂TiF₆ and APF solutions and determing the reaction products after treatment with (NH₄) ₂TiF₆ solution.
Human intact enamel was demineralized (Moreno, 1974) after treatment with (NH₄) ₂TiF₆ and APF solution (9000ppmF^-, pH 3.4) for 1hr following a synthetic saliva wash (Birkeland, 1973) for 24hr. The artificial caries-like lesions were investigated by polarized light microscopy, contact microradiography, SEM observation, EPMA, and X-ray diffractometry. A polarized light photomicrograph showed that control enamel surfaces had well-developed lesions, whereas the experimental surfaces had smaller lesions. After saliva wash and the formation of caries-like lesions, the SEM image showed that surfaces treated with (NH₄) ₂TiF₆ solution has a tenacious coating. EPMA revealed the distribution of titanium and fluoride in the caries-like lesions of enamel treated with (NH₄) ₂TiF₆ solution.
Human enamel powder (passed through 200 mesh) was treated with (NH₄) ₂TiF₆ solution (79.0 and 8.8 mM, pH 3.4) for 3, 5, 10, 20, 30, 40 and 60 min. at 37°C. Each solution was filtered and analyzed for calcium, phosphate, titanium and fluoride.
Gibbs' free energy was computed with respect to CaF₂, Fap and Hap in the experimental solutions. Two mol HClO₄ acid-insoluble product was determined with an analytical electron microscope. Organically extructed enamel powder was prepared to investigate the relationship between glaze and organic materials.
In the experimental solution (79.0 mM) free F^- increased for the first 10 min. and decreased slowly, and Ti⁴⁺ decreased for the first 10 min. and then kept almost constant. This result suggests that F^- and Ti⁴⁺ are disassociated from [TiF₆]^2-and react with enamel independently. ΔG showed that experimental solutions were supersatulated with respect to CaF₂ and Fap but not Hap. Acid-insoluble product, which was not formed in organically extructed enamel, contained titanium and phosphorus.
Human enamel treated with (NH₄) ₂TiF₆ solutions formed CaF₂, Fap and glaze-like product containing titanium and phosphorus and organic materials. The glaze-like product has strong acid resistance and it may act a major inhibitor of caries formation.

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[in Japanese]

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