This is one of a series of reports which compare the oral conditions of Tibetans from three different areas.
As regards occlusal features, crowding shows whether their jaws developed well or not.
1. In Karakoram, teeth were too abrased to know the original occulusion of the villagers' teeth because of fine sand mixed in cooking water.
2. In northwest Nepal, the crowding rate was smaller than than of Yunnan Province. On the other hand, the overjet rate decreased much among the villagers who were more than fourteen years old.
3. In Yunnan Province, the crowding rate was two times greater than in Northwest Nepal.
Much crowding was found in youngsters; one third of those five to fourteen years old proved to have crowding. Greater overjet rate was found among villagers who were older than fifteen years old than those who were five to fourteen years old.
4. As malocculusion data from a Japanese report on a survey of dental diseases were examined from the view point of orthodontic requirements, it is impossible to compare the malocclusion conditions with those from the three Tibetan areas.
The crowding rate found among five-to-fourteen-years old villagers in Yunnan Province was similar to that of Sakuta's data.

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Changes in microstructure induced by laser irradiation on demineralized dental enamel were examined by means of a combination of transmission electron microscopy (TEM) and selected area electron diffraction (SAED) techniques. Specimens for TEM and SAED examinations were prepared by ion-beam thinning. Dyes were not employed in the present study. Therefore, contrasts observed in TEM images were correlated directly with crystal structure found in SAED patterns. The surface layer of lased enamel was melted to a depth of approximately 0.5μm. The melted surface layer was solidified by crystallization. Amorphous regions were not found in the present study. But after laser irradiation was made at 134J/cm², the crystal structure consisted of hydroxyapatite only. No calcium compounds such as α-TCP and/or β-TCP were detected in the SAED patterns.

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In order to learn about the knowledge and attitudes of Japanese dental students concerning prevention of dental caries and dental education, a questionnaire study was conducted. The subjects were a total of 1571 6th year students in 17 Japanese dental colleges and schools, and we analysed their attitudes toward the community dentistry.
The results were as follows.
1) The rates of students who took a positive attitude to the main question of “Do you want to have your children participate in the fluoride mouth rinsing program in a future? (Participation)” showed wide gaps between Japanese dental colleges and schools (Max. =91.0%, Mini. =40.9%, Mean=65.2%).
2) The items which were correlative to the percentage of the students affirming participation were “Do you think that fluoride mouth rinsing is effective in the prevention of dental caries?” (“Effect”, Yes), “Which is more effective in the prevention of dental caries, fluoride mouth rinsing or tooth brushing?” (“Comparison”, Fluoride mouth rinsing) and “Were you taught about fluoride in a lecture on preventive dentistry?” (“Lecture”, well enough). Those results suggested that each item could be change by dental education.
3) A dental college which had a high positive score on the attitudes was selected for further examination. The change in attitudes of the students from the 1st to the 6th year was examined. We discussed which education factors were responsible for the observed changes in attitudes.

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In 1972 water fluoridation was begun in Chung-Hsing New Village, Taiwan and it was discontinued in 1986. At the first stage, fluoride concentration was 0.6ppm, and was changed to 1.0ppm in 1978. Chung-Hsing New Village is located about 20km south-east of Taichung city and the mean temperature is 73.4 degrees Fahrenheit.
In July 1991, to survey the dental effects in the 5 years after the water fluoridation discontinued, we conducted a dental survey in Chung-Hsing New Village and in Tsao-Tun as a control area. Two dentists examined dental caries with the criteria of WHO and one dentist examined dental fluorosis with Dean's criteria. The subjects in Chung-Hsing New Village were 93 schoolchildren aged 10-12 who had been drinking fluoridated water from birth to 5-7 years of age and 80 schoolchildren aged 14 or 15 who had been drinking from birth to 9 or 10years of age. In Tsao-Tun, the control group was 99 schoolchildren aged 10-12 and 78 schoolchildren aged 14 or 15. In the 10-12-year old schoolchildren, the mean DMFT was 1.19 (SE=0.17) in Chung-Hsing New Village and 2.55 (0.26) in Tsao-Tun. The difference was 53.3% (p<0.001). In 14 or 15-year-old schoolchildren, the DMFT was 2.38 (0.35) and 3.39 (0.34), respectively. The difference was 29.8% (p<0.05). The mean DMFS for each tooth type in Chung-Hsing New Vlliage was smaller than in Tsao-Tun. We found more effectiveness in the 1st molars and the incisors than in the other teeth. High caries preventive effects were produced by fluoride exposure not only in the calcification period, but also in the post-eruptive maturation period.
In both areas, we could not find moderate or severe dental fluorosis. The prevalence rate of dental fluorosis was low and the difference between Chung-Hsing New Village and Tsao-Tun was not significant. CFI varied from 0.05 to 0.15. The present study proved that the water fluoridation produced caries preventive effects and the favorable effects remained for 5 years after discontinuation of the projects. In addition, there was no public health problem of dental fluorosis.

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The purpose of this study was to examine trends in caries prevalence during 1970-90 in the junior high school students aged 12-15. A total of 840 children from 1st (12-13-yr-olds) to 3rd (14-15-yr-olds) school grade in the junior high school in Shizuoka city, Japan, was examined in 1990. The caries prevalence in 1990 was then compared with the data which had been collected from the longitudinal survey by Katayama (1970-72) and the cross-sectional survey (1985) on schoolchildren in the same junior high school. The results indicated that DMFT and DMFS indices in the 1st school grade in 1990 were significantly lower than in 1985 (p<0.05) and in 1970-72 (p<0.01). The DMFT indices at age 12-13 were 5.47 in 1970-72, 3.60 in 1985, and 3.09 in 1990. Percentage decreases in DMFT at age 12-13 were observed in the maxillary incisors (36%), maxillary molars (21%), and lower molars (13%) during 1985-90. The percentage decrease per annum of DMFT index at the age of 12-13 in the examined population was relatively low (-2.9%) in comparison with other industrial countries. Likewise, the downward trends in caries prevalence were apparent in the 2nd and 3rd school grades during 1971-85, but no significant change was observed between 1985 and 1990. The reason for the change during 1985-90 in this population is not clear, but the study shows that the frequency distributions provide valuable information for monitoring changes and high risk groups in caries prevalence.

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The purpose of this study was to evaluate the effects of a fluoride mouth-rinsing program (FMR) on dental health after the FMR program was completed. The state of dental health, including caries prevalence, was examined under blind recording conditions concerning participation in the FMR for 11th grade students in 10 public high schools, from 11 municipalities in Niigata Prefecture. The procedures of the FMR were carried out in these areas weekly, with 0.2% NaF, or daily, with 0.05% NaF, supervised by the classroom teachers in each school. The subjects, 321 in total, were classified into 3 rinse groups, each of which participated in the FMR for different periods of time, and a control group. The results of the statistical analysis showed increasing benefits in relation to increasing periods of participation. The reduction rate of caries prevention was the highest in the F11-group, subjects who participated in the program for 11 years from 4 to 14years of age. The F11-group was 56.0% lower in the mean DMFT and 81.8% lower in the mean number of highly progressed carious teeth than the control group, with statistical significance in both cases. The percentage of students who had toothaches or who were absent from school in order to visit a dentist was lower in the rinse groups than in the control group. We conclude that, in countries such as in Japan where caries prevalence is relatively high, a school-based FMR program throughout the school years is profoundly effective in preventing the occurrence and the progression of caries, and it could be the foundation of lifelong dental health care.

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We conducted research on the dental health and hygiene activities in schools and the number person-days per year for activities in order to examine the manpower volume of dentists and dental hygienists which is necessary to put into practice dental health and hygiene activities equally in all schools throughout the country.
The followinng results were obtained.
1) Periodic and preschool dental health examinations have been carried out in all schools throughout the country. However, the practic of other dental health activities was as low as 30% in primary schools and 20% in secondary schools.
2) In the schools which have carried out dental health activities, 70% of the dentists among all the schools joined in every activity and 30% to 67% of the dental hygienists among all the schools joined in every activity excepting dental meetings.
3) The mean number of yearly average of person-days for dental activities for a school was different according to the number of schoolchildren. Primary school dentists worked for 3 to 10 person-days and secondary school dentists for 2 to 8 person-days. They alotted 70% of all the person-days for dental examinations. Dental hygienists assigned 2 to 5 person-days in primary schools and 1 to 2 person-days for average yearly dental activities.
4) The yearlong activity person-days for a school practicing in the dental health activity were subdivided into the values of 50%, 75%, 80%, and 90% by the number of schoolchildren for the dental examination. The necessary yearly activity person-days were from 5 to 13 (50%) and 13 to 31 (90%) for the dentists, and 11 to 16 (50%) and 24 to 43 person-days (90%) for the dental hygienists.
5) The necessary yearly person-days (50-90%) according to regions were 9 to 20 person-days for a dentist and 26 to 63 person-days for a dental hygienist in towns and villages of 10, 000 people, and 5 to 12 for a dentist and 15 to 37 for a dental hygienist in cities and wards of 50, 000 people, and 4 to 8 person-days for a dentist and 10 to 25 person-days for a dental hygienist in cities and wards of 100, 000 people.
6) The yearly manpower volume necessary for the school health activity of a school was obtained from the dentists and hygienists and we suggested that more hygienists will be needed in the future.

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