A STUDY ON ASPECT OF ERUPTION AND OF SIX-YEAR MOLAR TEETH DECAY

Abstract

Five typical paterns were at first selected regarding to the conditions of eruption of six-year molar teeth. This was applied to and investigated on 5647 males and 5722 females of from 3 to 17 years of age youngsters of from nurseries and kindergartens to high schools. Research was made on change of types of eruption by age.
1. At the age of 4, years eruption of six-year molars can not still be seen, but it starts at around 4.5 years old and by 5-6 years about half of them have at least 1 six-year molar.
2. Complete eruption (4 full six-year molas) reaches at the age of 6.5-7.0.
3. It is well to be supposed that eruption of six-year molars is generally earlier in females than in males.
4. Generally speaking, no difference is noted among children of nurseries and kindergartens.
With regard to the caries of six-year molars, because of the period between the first eruption of six-year molarand the completion of the eruption is short, decaying is seldom seen. Incidence percent of caries of 4 erupted teeth increases along with the advance of age.
An observation was made on accumlative curve which shows break-downs of decaying types by change of ages.
Following results were obtained
1. Trend of decaying of six-year molars ups in straight line from 4 to about 11 years of age.
2. With regard to one decayed tooth' no difference is noted between both sexes; but frequencies of 2, 3 and 4 decayed teeth seem to be higher in females by each age than in males.
3. To obtain general percentage of patients of decayed teeth straight line system was taken for from 4 to 11 years of age. This straight line is presumed that it is generally well fitted to the actual conditions.