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Dental caries in school children has not decreased to a level corresponding to the efforts made to prevent it. As the caries prevalence in permanent teeth is very high during the period of compulsory education, the effective caries prevention should be promoted during this period. Therefore, it is considered valuable to survey the real state of caries prevention and provide school dental health service according to the results of survey. Yearly observation of the changes in oral conditions of same subject gives reliable results. In this study, I made a survey of dental caries prevalence on permanent teeth of school children for 9 years from the age of 6 years until they graduated from middle high school, and I preformed cumulative analysis of variance of multiple-way layout of the results. The decomposition of factors was also followed to exhibit the difference in caries prevalence between different kinds of teeth or tooth groups which have not completely analyzed been so far.
I obtained the following results.
Caries prevalence during the period of compulsory education increased by 2.85 carious teeth per year and its regression equation was as follows;
Y (DMF) =2.85X (school year) -0.78
The tendency of caries prevalence in different kinds of teeth or tooth groups was varied and the dental health care for younger and older primary school children and middle high school children should be focused on the first molar, incisor of upper jaw and premolar, and second molar, respectively. Moreover, the comparison of these results with those of commonly used cross sectional studies showed much similarity. I also suggest that the caries prevalence of the first molar could represent the tendency of the whole dentition.
The statistic analysis used for the first time in this kind of survey was useful to analyze yearly data or the data from different kinds of teeth or tooth groups.

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The relationship between aging and fluoride administration was studied in Donryu rats. In a preliminary study, rats were continuously fed with an 18% casein food until spontaneous death, and the aging process was divided into the following 3 stages: 4, 15 and 60 weeks of age. In the actual study, rats were fed with the 18% casein food and fluoride was added to the food for a period of 4 weeks starting at 4, 15, or 60 weeks of age. Animals were killed after completion of the 4-week fluoride administration. The incisors, molars and femur were excised in order to determine fluoride levels in these hard tissues.
1. The inhibition of body weight gain was greater in older rats and in those which received greater doses of fluoride. In particular, body weight loss was noted in those which received fluoride starting at 15 or 60 weeks of age.
2. Food consumption decreased as fluoride concentration in food increased in older animals.
3. As fluoride doses increased, fluoride levels increased in dentin of incisors and molars and in femurs.
4. Fluoride levels in hard tissues tended to decrease with aging but only slightly in the dentin of incisors.
5. The effect of aging was significant in molar dentin in which fluoride levels decreased significantly in 15-week or 60-week old rats as compared to 4-week old rats.

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Symptoms of functional disturbance of the masticatory system are clinically important subjective signs of the periodontal patient. Therefore, evaluation of the masticatory function during initial treatment of periodontal disease is an effective means both for motivation of the patient and to assess the improvement of the disease. This investigation was aimed to establish a method for clinical measurement of biting force using healthy volunteers.
Twelve adults, 6 men and 6 women, participated in this study. The biting force of the first premolars at the upper left and lower right were measured by strain gauge. The subject was instructed to bite 6 times as hard as possible, each for 5 seconds at intervals of 15 seconds. After 2 minutes' rest, an identical series of 6 bitings was performed. A third series was also conducted after 5 minutes of rest.
The biting force increased gradually and reached a plateau after several trials. The mean value of the biting force was significantly different between the first series and the second or third one, but not between the second and third series.
It appears that the mean value of the second series can be used as the representative biting force of the subjects. The applicability of the value as an indicator for the assessment of masticatory function of periodontal patients is discussed.

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The purpose of this study was to examine the development of dental caries and dental plaque accumulation on rat molar teeth exposed earlier than the normal eruption and with the opponent teeth extracted. These treatments were applied to the upper left first molar. The normally erupted upper right first molar of the same animal served as control. The rats were fed on Diet #2000 and distilled water after weaning ad libitum. Three types of experiments were made in this study: (1) rats were kept for 30 days after weaning, and caries and dental plaque accumulation were examined; (2) rats were kept till 27 days after birth, and caries and dental plaque were examined longitudinally through weaning to the end of this experiment; (3) rats were kept for 22 days after birth, and the total amount of plaque and microflora in the plaque were examined from the 17 th to 22nd days.
The results were as follows.
1) In the first experiment, the teeth without opponent teeth and the prematurely exposed teeth without opponent teeth had a caries cavity score, caries fissure score, and plaque score higher than teeth of the control group and control side. Especially, in the teeth with double treatment, dental plaque accumulated and caries developed remarkably more than in the teeth with single treatment. (Fig. 2, 3, 4)
2) The prematurely exposed teeth and the teeth with the opponent teeth extracted showed much dental plaque accumulation at weaning and developed dental caries earlier than the control teeth. The prematurely exposed teeth and the teeth without opponent teeth developed caries in the enamel at entrance of fissures. Moreover, the double treatment caused more rapid carious development. (Fig. 6, 7)
3) Microflora in dental plaque showed no difference between the experimental side and the control side.
Consequently, I concluded that carious incidence and development were affected by two factors, enamel maturation and the period from eruption to occlusal beginning.

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The purpose of this study was to examine the factors in the dental caries incidence and the eruption of first molars. The subjects of this study were 177 school children who were born in 1976-1977 in Tomisato-cho (Chiba). The dental examination was carried out 20 times during the period from May, 1982 to July, 1985. Only first molars erupted in the survey period were used for the analysis. The following seven factors were selected (1) dmft (exclusion of deciduous incisors), (2) the age at the eruption time of the first molar (months), (3) the height of the children at the eruption time (cm), (4) length of the erupting periods of the first molar, until contact with the opponent tooth (months), (5) the plaque accumulation (OPI) on the occlusal surface before the beginning of the occulusion, (6) the plaque accumulation (OPI) on the occulusal surface after the beginning of the occulusion, and (7) the dental caries on the deciduous second molar (rate of decay). Discriminant and analysis was used in order to evaluate the relation between these factors and the incidence of dental caries on the first molar.
The Lower first molar erupted earlier and took longer time until contact with the opponent tooth than the upper first molar. Moreover, the lower first molar had more dental plaque on the occlusal surface than the upper first molar before the beginning of the occulusion.
The dental caries on deciduous teeth was related to the eruption time of the first molars. In particular, severe caries on the lower second deciduous molar seemed to hasten the eruption of the lower first molar earlier and to delay the beginning of occulusion as a result. Discriminant analysis indicated that the dental caries in deciduous teeth was related closely to the incidence of dental caries in first molars.
From these results, we concluded that for caries prevention in first molars the prevention of caries in deciduous teeth, particularly in the second deciduous molars is important.

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Fluoride is widely distributed throughout the body. In order to determine patterns of fluoride distribution in the body, ionic and whole fluoride levels as well as Ca levels (which have great affinity with those of fluoride) were determined in maternal and umbilical cord blood serum obtained during delivery.
Both ionic and whole fluoride levels in maternal and cord blood serum showed almost normal patterns of distribution. Similar patterns were also observed for serum ionic and whole Ca levels. Although mean ionic fluoride levels in maternal and cord serum were comparable, whole fluoride levels in cord blood serum were significantly lower than those in maternal blood serum.
A significant correlation was noted between ionic fluoride levels in cord blood serum and those in maternal blood serum. Ionic Ca levels in cord blood serum and those in maternal blood serum were also significantly correlated. In contrast, ionic and whole fluoride levels and ionic and whole Ca in maternal and cord blood serum were not significantly correlated with each other.
These results suggest that the placental barrier blocks the transfer of maternal fluoride to some extent.

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In order to study the effect of dietary lead in rats, a study was performed to evaluate changes in lead and zinc concentration in hard tissues, as well as changes in aminolevulinic acid dehydratase (ALA-D activity), a major parameter of lead intoxication.
Rats were given 1m mol/kg of lead or 1m mol/kg each of lead and zinc for 3 consecutive weeks after a conditioning period of 1 week at 3 weeks of age, and the effect of zinc on lead concentration was evaluated.
Body weight was significantly decreased in the lead group compared to the controls (P<0.05). Kidney weight tended to decrease in the lead + zinc group compared to the lead group.
Lead concentrations in femur, mandible, and molar dentin were lower in the lead + zinc group than in the lead group (P<0.05), and the opposite was true for zinc concentration (P<0.001).
As in hard tissues, lead concentrations in the liver and kidneys were much lower in the lead + zinc group than in the lead group (P<0.01 and P<0.001, respectively). However, zinc concentration was not affected by administration of zinc in the lead + zinc group. Blood ALA-D activity was lower in the lead group than in the controls (P<0.01). A slight recovery was seen in ALA-D activity after simultaneous adiministration of lead and zinc but the activity level remained below the control level. Lead concentrations in the femur and mandible and those in molar dentin and enamel were singnificantly correlated in all experimental groups.
These findings suggest that lead concentrations in hard tissues of rats can be decreased to some extent with concomitant lead and zinc administration.

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Junior high school children (1, 218) were examined to assess the prevalence of gingivitis. The mouth was divided into 12 segments. The number and the location of the segment which had inflammation was scored for each child. Deposition of plaque and calculus were also scored as negative or positive.
The results obtained were as follows:
1. The average number of segments which had inflammation was 5.9 per child and 96.9% of the children had gingival inflammation in at least one of the segments.
2. The segment which showed the highest prevalence of inflammation was at the labial side of the lower anterior teeth followed by the labial side of the upper anterior teeth.
3. The children assessed as plaque-free were only 3.3% and 46% of the children showed calculus deposition.
It was concluded that the promotion of periodontal health in junior high school is very important.

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[in Japanese]

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