The nature of in vitro enamel lesions was investigated with changing degree of saturation (DS) of demineralizing lactate buffers with respect to enamel. Microradiographs of enamel thin sections before and after demineralization were analyzed with a computer image analyzer. We particularly examined whether the presence of fluoride ion (F^-) is indispensable for the development of subsurface lesions with a relatively intact “surface layer”. The trace amount of fluoride in the buffers was purposely removed, so that possibility of the precipitation of fluorapatite would be substantially eliminated. The present study demonstrated that, for a given DS value, the lesions changed from cavitations to subsurface lesions, to no detectable mineral loss with increasing F^- concentration. Similarly, for a given F^- concentration, the same lesion sequence was obtained with increasing DS value. The “surface layer”obtained in fluoridated buffers with 1 ppm F^- had a higher mineral content, due to initial dissolution of enamel and precipitation of fluoridated apatite. On the other hand, even in the F^-removed buffers which were estimated to be under-or slightly supersaturated with respect to fluorapatite, subsurface lesions were observed. The finding suggests that the subsurface demineralization could be caused without precipitation of fluorapatite. These results clearly show the dynamic nature of caries-like lesions.

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There is little information about the pattern of fluoride distribution in human bones relative to sex and age. The present study is the first of its kind to be undertaken to determine in detail the fluoride distribution profile in human bone.
Human ribs were obtained from 119 patients (M: 72, F: 47) aged 20 to 93 yrs. The fluoride distribution from the periosteal to the endosteal was determined in each specimen using the abrasive micro-sampling technique. Fluoride was determined using the fluoride electrode as previously described by Hallsworth, Weatherell and Deutsch (1976), and phosphorus was determined by the colorimetric procedure of Chen, Toribara and Warner (1956).
The concentration of fluoride was highest in the periosteal layer and then decreased gradually towards the interior of the tissue. The amount of fluoride leveled off and then rose again just before the endosteal surface. The difference between periosteal and endosteal fluoride increased with age. Overall, fluoride concentrations increased steadily with age in male subjects but leveled off until the age of 55 yrs and then increased markedly in female subjects over the age of 55 yrs.

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[in Japanese]

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We have already investigated the incidence of congenital abnormalities of deciduous teeth including fused teeth, congenitally missing teeth, peg-shaped teeth, and supernumerary teeth in threeyear-old children. The purpose of this study was to compare the incidence of congenital abnormalities of deciduous teeth in Chinese children with our data. The subjects in Japan were 12, 812 children aged three years who visited a Public Health Center in the east district of Fukuoka City for oral examinations during 1983-1990. The subjects in China were 10, 804 children aged from two to six who lived in Shanghai City during 1989-1990.
There was no difference in sex of the incidence of congenital abnormalities of deciduous teeth between Japan and China. Total rate of incidence of congenital abnormalities was 7.42% in China, and 4.89% in Japan. The incidence of supernumerary teeth was 0.44% in China, and 0.01% in Japan. In Japan, the incidence of fused deciduous teeth on the right side was significantly higher than that of the left side (p<0.005). The incidence on the left side was significantly higher than on the right side (p<0.005) in China. Most fused teeth were found in the lower teeth in both countries. Fused teeth were mostly found in central and lateral incisors in Japan, but most fused teeth were found in canine and lateral incisors in China. Unilaterally occurring fused deciduous teeth were detected more frequently than bilaterally fused deciduous teeth in both countries, but no significant difference was observed between Japan and China.

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Japanese children still have a lot of dental caries at twelve years of age. Manpower and resources are not safficient to promote a preventive program of dental caries for school children. If we can predict high-risk caries groups early, it will be possible to control dental caries of school children efficiently.
We analyzed the relationships between DMF teeth in 12-year-olds and the factors concerning the dental caries onset of first permanent molars. Then we made equations for predicting caries highrisk groups early by the multiple regression analysis and the discriminant analysis.
The results were as follows.
1) The degree of caries prevalence of the first permanent molars was in accordance with that of the decay at the neighboring second deciduous molars.
2) The degree of the decay at deciduous second molars and the number of deciduous teeth caries were significantly related to DMF teeth in 12-year-olds.
3) A multiple regression analysis using eight variables showed that we could get an equation with a much higher multiple correlation coefficient.
4) The predictive equation for discriminating the high-risk caries group which had 5 or more DMF teeth at the age of 12 worked very correctly.
5) The equation using two or three variables was worse than eight variables in ability of prediction, but it was nevertheless useful.

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[in Japanese]

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The purpose of this study was to investigate the clinical effect of dentifrice R containing 0.05% tranexamic acid and 0.05% dipotassium glycyrrhizinate on the improvement of periodontal disease compared with dentifrice T containing 0.05% tranexamic acid.
Subjects were 148 adults who had no serious oral or systemic diseases. They were divided into two groups equally and performed toothbrushing twice a day for four weeks with dentifrice R or T.
The PMA index, redness, swelling, and plaque score were selected as indices for clinical evaluation of periodontal condition.
The results obtained were as follows.
1) Dentifrice R was significantly superior to dentifrice T in the improvement of PMA index (p<0.01), redness (p<0.01) and swelling (p<0.05). There was no significant difference in the improvement of plaque score between dentifrices R and T.
2) The mean improvement rates of dentifrice R and dentifrice T were 37.0% and 26.3% in PMA index, 40.7% and 25.2% in redness, and 36.7% and 29.9% in swelling, respectively.
3) No particular side effects were observed during this clinical study.

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In this study, the fermentation ability of D-mannitol in children's mixed saliva was determined by a simple API 20 Strep® system. The relationship between the salivary fermentation ability of D-mannitol and the number of mutans streptococci in the saliva was elucidated, and the connection between salivary fermentation ability of D-mannitol and dental caries activity was also investigated. According to the increase in number of mutans streptococci in the saliva, the number and percentage of saliva samples which exhibited a positive reaction to D-mannitol significantly increased (p<0.001). When the number of mutans streptococci in the saliva samples was more than 10⁵ CFU/ml, 100% of the saliva samples exhibited a positive reaction to D-mannitol. By using bacteria cell suspensions of reference strains, the number of mutans streptococci, which was >1.5×10⁵ CFU/ml to >5.0×10⁶ CFU/ml, exhibited a positive reaction to D-mannitol. During a 6-month period after the sampling, the dental caries significantly developed in the children with saliva that exhibited a positive reaction to D-mannitol. These results show the possibility of using a salivary fermentation test with the API 20 Strep® system for a caries activity test as reflected by the number of mutans streptococci.

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Awareness of periodontal disease is often dismissed due to lack of sufficient early symptoms of disease onset. Therefore, we developed a self-administered questionnaire for periodontal disease consisting of 45 questions concerning life style, bacterial plaque, brushing, foul breath, gums, acute and chronic symptoms of periodontal disease, experience of dental treatment, health guidance, and dental knowledge for general use by adult subjects to check their periodontal health without professional guidance. Each questionnaire item consisted of 4 alternative categories.
Validity of the returned questionnaires from 283 office workers (193 males and 90 females aged 18-62 years) was quantitatively evaluated by comparing with the data obtained from clinical periodontal examinations. A total of 20 questionnaire items such as brushing habits, gum condition and chronic symptoms were statistically correlated with the severity of periodontal disease.
In this study, we defined these 20 items as the explanatory variables influencing the severity of periodontal disease and both subject groups selected on the basis of gingival index as objective variables. Results of analysis by the Quantification Theory II indicated that 20 items of the self-administered questionnaire were closely related in discriminating between periodontally sound and affected subjects (rate of correct discrimination: 72.8%, sensitivity: 91.4%, specificity: 43.1%). These results suggest that our self-administered questionnaire is effective as a self-check for periodontal disease.

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The progression rate of newly occurred pit and fissure incipient caries of first molars was investigated every 6 months for 24 months. The subjects were 93 1st and 2nd grade elementary school children who did not perform school-based fluoride mouthrinsing. The progression rate after 12 months was approximately 60%, and the non-progression rate was approximately 40%. Cumulative progression rates after 12 months were approximately 60% for the 1st grade, and 40% for the 2nd grade, and the same rates after 24 months were 70% for the 1st grade, and 60% for the 2nd grade. These data were compared with our previous data derived from the same grade of elementary school children who performed school-based fluoride mouthrinsing. There was no statistical difference in the progression of incipient caries between these two schools. This lack of difference may be explained in terms of the complicated form of pits and fissures, or it may be that the fluoride mouthrinsing period was too short to be effective against caries progression.

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We report the results of a questionnaire survey of training in a health center. The training program, in the school of dental medicine of Tsurumi University, was begun in 1976 and is still being continued. The opinions and impressions of student assessed by questionnaire and analyzed by cross-table, and Hayashi's theory quantification type II. The students primary interests in this training program were divided into three groups. The groups are illustrated in a scatter diagram by discriminate score. The sum of category scores, employment in public health services, attendance at training classes, observation of the examination of 3 year-old infants, and comprehension of administrative methods contributed to interest in the training. Some comments for training are given.

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171 human premolars which had been extracted for orthodontic purposes were divided into two groups. The first group, consisting of sixty specimens, were coated with nail varnish leaving a “window” at the enamel-cementum junction on the mesial or distal approximal surface, and placed in acidified gel pH 4.5 (Silverstone 1966), for periods of 1, 2, and 4 weeks. After exposure to the acidified gel, the specimens were sectioned longitudinally without embedding through the middle part of the “window” and examined. The second group of 111 specimens were first sectioned longitudinally in a mesiodistal plane and classified into three types on the basis of the morphology of their enamel-cementum junction. In Type I the enamel and cementum did not meet leaving a narrow region of exposed dentin; in Type II the enamel and cementum just met; and in Type III the cementum overlapped the enamel. From these sections ten examples of each type were selected. After this they were coated as before with nail varnish leaving a narrow “window” on the tooth surface with the enamel-cementum junction exposed. The sectioned specimens were then placed in acidified gel for a total of 168 hours and examined serially after 5, 10, 15, 20, 30, 40, 50, 60, 80, 100, and 168 hours. The lesions of these specimens were examinined by transmitted and polaraized light microscopy, contact microradiography, SEM, and XMA.
Results: In both groups the artificial caries-like lesion of the root surface could be divided into 6 layers from surface to bottom. In light microscopy, the first layer was a slightly translucent zone which had on an intensely opaque surface and bottom, and that corresponded to acellular cementum, the second layer was a very translucent zone, the third layer was a slightly opaque zone, the fourth layer was a slightly translucent zone, the fifth layer was a very opaque zone, and the sixth layer was a very translucent zone.
In microradiography the first layer was a considerably demineralized zone which had a very opaque surface and bottom, the second layer was an intensely demineralized zone, the third layer was a slightly remineralized zone, the fourth layer was a demineralized zone, the fifth layer was a considerably mineralized zone, and the sixth layer was an intensely mineralized zone.
Although the remineralization of the surface of the first layer became unclear as the demineralization process progressed, the remineralization on the tooth crown side and on the root apex side, where the initial demineralization was expanding, could be clearly observed.
The lesion in acellular cementum progressed along the Sharpy fibers, enlarging the portion which enclosed the Sharpy fibers. Although the lesion in the dentin progressed along the dentinal tubules, it did not progress along the incremental lines. On the tooth crown side the lesion also progressed along the enamel-dentin junction.
In the Type I enamel-dentin-cementum lesions the dentin which was exposed became demineralized and the profile on the tooth crown side was deep and rounded. On the other hand in the Type III specimens with cementum overlapping the enamel, the lesion in the dentin was shallow with a sharp profile.
It is concluded that the structure, progression, and expansion of artificial tooth root surface caries-like lesions are dependent on the chemicophysical phenomenon by demineralization and the natural histological structure of this site.
It is believed that the findings of this study will be useful for a better understanding of the progression of natural tooth root surface caries lesions.

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In 1984, a program for dental caries prevention was started in Hisayama Town, Fukuoka Prefecture, Japan. The program consisted of dental hygiene instruction and fluoride application. The 1.5- to 3-year age group were recalled every 3 months after the initial dental examination and received dental health instruction and topical fluoride application with APF (2% NaF). Kindergarteners and primary school children rinsed their mouths with 0.2% NaF once a week, and were given dental health instruction and a dental examination twice a year. Junior high school students were given a dental examination once a year.
Comparing the improvement of dental health status between 1984 and 1990, dental caries prevalence decreased in all age groups of subjects, particularly in the higher grade children in primary school. The DMFT index and DMFS index in 1990 decreased less than 50% compared with those of 1984. The dft index of the 5-year age group decreased from 9.32 to 6.40, and the DMFT index of the 12-year age group decreased from 5.13 to 2.34.
Presumptive calculation of cost for caries treatment was estimated from the chart of dental examination in primary school. Thus, the cost for caries treatment was calculated by using a standard taken from the table of numerical rating of health insurance issued on April, 1990. It was estimated from the survey that a total of 12, 300 yen per child during the 6 years of primary school was saved in this dental health service.
The purposes of this program were “DMFT index less than 3 at the age of 12”, and“dental treatment for all decayed teeth”. The first purpose was achieved in this 6-year period. Concerning the latter purpose, the mean number of decayed teeth decreased to one third of that in 1984.

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