| Budget Amount *help |
¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2000: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
In a Japanese population, the lower first molar erupted earlier than the lower central incirsor before. The Japanese Society of Pedodontics (1988) reported contrary result for the eruption pattern. This phenomenon includes an important problem from a biological viewpoint, because the first erupted permanent tooth is changed from supplemental tooth (the first dentition) to the successional tooth (second dentition).
We investigated the eruption pattern of the central incisors and first molars in individuals to clarify the starting generation of this phenomenon. It was found that "I" type, which central incisor erupted earlier than the first molar, was increased in Japanese infants who was born at 1970's, and became 50% or more.
The comparison was made between the two previous studies (Okamoto, 1934, 1938 ; JSPD, 1988) and among the pervious studies of other ethnicities to discuss the change of the eruption timing. The following conclusions were obtained : (1) The life style of Japanese rapidly changed from traditional to the European or North American styles from 1970 onward. This change of the life style including eating habit is thought to be a candidate factor of this phenomenon.(2) Early development of the secondary dentition caused this phenomenon directly.(3) We propose to add IIB stage (exchange period of the incisors) in the Hellma's dental stage, if "I" type will be more frequently found in the Japanese children.
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