The mercury materials concern as environmental pollution. Ikejiri, et al (1971) and Aoki reported the oral symptoms of the fetal Minamata Disease. The dental profession used mercury about 4% of the total amount used in the U.S.. The hazards of health have brought in dental office and its auxiliary. Under these situation, the mercury content in human teeth couldn't contact untill Kitamura and Kusaba (1975) used the non-flame atomic absorption spectrophotometer. In this report the mercury concentration was studied in the Minamata Area, which reduced ramdomly. 1. The mercury concentration in normal teeth at Minamata and control area showed no significant difference. 2. The mercury concentration in the age group of forties was significantly higher than that of twenties. 3. The teeth-age was defined as the term after the eruption. The teeth-age of thirty which were erupted during the Chisso plants increasing the production were higher level of mercury than the teeth-age of twenty that of after the World War II. 4. The mercury level in dentine carried the some correlation between the mean concentration of the teeth-age. 5. Kitakyushu, et al and Minamata were situated under the same environmental condition because the mean level of the teeth-age had almost same transition. The Minamata Disease could be reconsidered from the causal point of views. 6. The mercury concentration in normal adult teeth with the Minamata Disease reached slightly higher than that of healthy person. 7. The four degree of caries indicated higher level of mercury concentration which was caused from enamel substance. The enamel of caries could suggest the oral hygine situation. The mecury level was analyzed in each group. The term of teeth-age reveals the retrospective mercury level in person and the environmental condition.

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Abnormalities of teeth can frequently be observed clinically. Recently we experienced a rare case of 11 years female who had enamel hypoplasia, and enamel hypoplasia was apparent on [numerical formula]. One fundamental cause of this enamel hypoplasia may be attributed to acuta feverish disease in the period her dental growth.

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Abnormalities of teeth can frequently be observed clinically. Abnormal cusp includes incisor tubercle, canine tubercle, central cusp, Carabelli's cusp, paramolar cusp and distomolar cusp. Nor recent experience of the complicated case of abnormal cusp and palatal invagination has been reported. Recently we experienced a rare case of 20 years female who had abnormal cusp and palatal invagination of |2__-.

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