A STUDY ON THE POSSIBLE CORRELATION OF PERMANENT TOOTH ERUPTION WITH THE PHYSIQUE OF YOUNGSTERS 6 TO 15 YEARS OF AGE

A cross section survey for the year 1968 was conducted on the possible correlation existing between the physique and the permanent tooth erupution in younger generations, using a total of 5, 508 subjects of both sexes consisting of those regional groups who resided respectively in Yawata of Kitakyushu metropolitan city, Nakatsu city and its suburban small industrial and farming communities. The permanent tooth eruption was studied with respect to relative speed at which individual teeth came into full eruption by calculation of correlation and regression coefficients and by analysis of covariances. Results obtained were as follows. 1. There was noticed some regional difference in the eruption time of the permanent dentition in that the eruption was earliest in Nakatsu group, followed by the rural community groups and Kitakyushu metropolitan group. 2. Study on the pattern of frequency distribution curve with regard to the number of erupted permanent teeth showed that L type was observed to occur in subjects 6 to 7 years of age and the normal type of curve occurred more or less in subjects 8 to 10 years of age, while J type was more frequently observed in older age groups toward 15 years of age. This change of patterns from L type to J type with advancing age was seen earlier in the female subject groups than in the opposite sex groups. 3. The relative speed with which individual teeth came into eruption was referred to as the eruption grade and studied comparatively among teeth. The time required for any tooth to reach its normal occluding position from their incipient stage of eruption was referred to as eruption time comprising 3 successive stages. The shortest eruption time required for incisors and first molars was from 5 to 7 years, and the time required for canines, first and second premolars and second molars was in the range from 7 to 9 years. 4. physique and Eruption of Permanent Teeth When correlation between the permanent teeth eruption and the physique of subjects of both sexes in every age stages from 6 to 15 years was studied, it was shown that the correlation coefficient with body weight ranged from -0.12 to 0.51 for the male sex, -0.21 to 0.54 for the female, and that with body length-0.09 to 0.50 for the male and -0.55 to 0.41 for the female. Although the correlation of the physique of subjects of both sexes with the number of permanent teeth eruption could be concluded to be highly significant in general, the values of coefficients obtained for each age stage differed considerably. Nevertheless, general trend showed that the correlation was strongest in youngest age groups and became gradually smaller from 6 years toward 15 years of age of subjects as shown in the regression line. 5. Covariance was calculated by analyzing the correlations of the permanent teeth eruption with each of age, body length and body weight of subjects. The results showed that the correlation between age was stronger than the ones between either body length or body weight. All these aspects of correlations between physique and permanent teeth eruption were studied perspectively by means of correlation coefficient and regression line as calculated for every age stages of subjects from 6 to 15 years of age. The results showed that the correlation coefficients for all class (age, body length and weight versus permanent tooth eruption) and for between class (age versus permanent tooth eruption) were far greater than those for within class (body length and weight versus permanent tooth eruption).