Continuous observations were made on a total of 189 pupils, 89 boys and 100 girls, who were admitted as first grade pupils to two Grammar Schools in two villages outside of Tokyo City for a period of 9 consecutive years since 1949, having followed their physical and dental development.
Measurements of height and weight and oral examinations were conducted four times a year, -April, July, October and January-making plaster models by taking alginate compound impres sions on both jaws, which totaled 13, 608 impressions and models of 72 consecutive models per examinee.
Parallel studies were made on a total of 11, 060 girl students ranging from 1st to 3rd grades of 14 Middle Schools in Tokyo and 2 others in Chiba Prefecture.
Surveys on menoplania were made every month for a period of 30 months during 1956 through 1958. Measurements of height and oral examinations were made on those at menoplania to determine the time element of parmanent teeth eruptions and to observe the growth and development of teeth.
Having observed the time element of permanent teeth eruptions from the view point of height development and age, the frequency by the height factor demonstrated extremely narrower range than by the factor, i. e., it was learned that the height has much closer relationship with the eruptions than the age, as it had been known.
It has also come to the attention that the eruptions of the second molar have closer relations with menoplania, therefore, observations were made on 1, 458 girls on whom the meneplania and the eruptions of permanent teeth were precisely determined.
Examinee were segregated into five types; Type I with all four second molar eruptions, Type II with three, Type III with two, Type IV with single and Type V with no second molar eruptions.
The Type I amounted to 81.41% of the total examined, and it was revealed that the menoplania coincided with the eruptions of bilateral second molar on both jaws.
The average height and age of the Type I, or at the time of menoplania was 149, 5 cm and 13 years 6 months respectively.
