永久歯の生歯度による生歯時期と齲蝕発病時期の研究

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Tooth eruption has been clinically considered to cover a definite time interval from the moment of the first appearance of a section of tooth crown on the top of alveolar ridge until full exposure and attainment of the crown to the occlusal position. In the present study, the whole process of permanent tooth eruption was divided into 4 consecutive stages or degrees according to sizes of tooth crown as it appeared into the mouth, and the 1st to 4th degrees of eruption respectively refered to 1/3, 1/2, 3/4 and 1/1 the full size of crown appearance in the mouth. By means of alotting the coefficients, 0.3, 0.5, 0.75 and 1.0 to each of the above 4 degrees of eruption, frequency of each degree for individual teeth was converted so as to obtain eruption rate and time, M^^-_2, F^^-_2 for the male and female subject groups respectively. Studies on the incidence of dental caries among primary and secondary school children have so far relied on DMFT as an important indicator under a general notion that individual permanent teeth has the same degree of eruption. The present study undertook to investigate the rate of DMFT of individual teeth with reference to different degrees of eruption shown by each tooth, and following results were obtained. 1. Frequency of Eruption of Individual Permanent Teeth Hardly any difference was noted in the frequency of eruption among pairs of the same named teeth on both sides of upper and lower jaws. The frequency of eruption, however, was higher in the teeth of lower jaw than in those of upper jaw, and was lower in teeth of the male subjects than in those of the female subjects. When individual teeth were compared, the first molar showed the shortest period of time for completion of eruption through both sexes of subjects, followed by central incisors, lateral incisors, 1st premolars and 2nd premolars in order. The canine and the 2nd premolar were the latest in the completion of eruption. The frequency of eruption as examined within limit of one year period was slightly smaller when the degree of eruption was taken into account. 2. Eruption Time of Individual Permanent Teeth Symbols M^^-_1 and F^^-_1 were arbitrarily given the conventional eruption time for male and female groups of subjects, and symbols M^^-_2 and F^^-_2 were respectively given to the eruption time adjusted by the degree of eruption in both sexes groups. Results showed that the female had earlier eruption time than the male in both cases as illustrated by the formulae, M^^-_1>F^^-_1, M^^-_2>F^^-_2 and M^^-_1>M^^-_2, F^^-_1>F^^-_2. 3. Rate of DMFT Comparison in the rate of DMFT between antagonizing teeth of four quadrants did not yield any noticeable difference of statistical significance within the same sex group. The rate for the male being ranged from 14.3% to 32.4% and the one for the female from 11.8% to 28.5% and the rates for both sexes being increased during the interval from 72-84 months to 180-192 months of age. Generally, every teeth in the female suffered dental caries after eruption earlier than in the male, so that the teeth except the cuspids in the female showed signs of incipient caries as early as one to two years after eruption. When the degree of eruption was taken into consideration, caries lesion was first seen almost during the period of 4 degree of eruption and in fewer cases at 3 degree of eruption. The relation between the degree of eruption and the time of caries incipience may be understood more fully, if teeth were observed in detail by classifying them into groups divided at every 4 months of age after completion of eruption. 4. F-T Rate There was no appreciable difference in F-T rate between the teeth on both sides of the same dental arch nor between those of upper and lower jaws. The rate for the male was 20.0% and for the female 22.7% at 72 to 84 months of age, both of which increasing with progressive age and reaching respectively 55.0% in the male and 59.8% in the female at 180 to 192 months of age.
九州歯科学会の論文
1976-09-30

永久歯の生歯度による生歯時期と齲蝕発病時期の研究

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