1) Strontium-90 level was determined in May 1989 in 40 sample groups of Japanese teeth, for a total of 1022 third molars, obtained from donors born in 1900-1970.
2) The teeth from donors born in 1925-1931, and which were extracted in the donors' twenties did not contain detectable strontium-90.
3) Strontium-90 level of the teeth from donors born in and after 1942 suddenly increased, and reached peak value of 62.8 to 72.8mBq/g Ca in 1953. It abruptly decreased after 1954 and reached approximately 20mBq/g Ca by 1970.
4) In the teeth obtained from donors born in 1900-1924, and which were extracted at the age of 30 to 69, a small amount of strontium-90 was detected.
