In oral diseases, tooth decay is one of the two most common diseases. It develops early from 2 yearolds. According to the survey of the Odontology Institute in 2001, the older people are, the higher rate of permanent tooth decay is. At the age of 6-8, rate of permanent tooth decay is 25 percent. And at the age of over 45, it is 90 percent. Althought tooth decay have rarely dangerous applications, but it is a popurlar disease. Other organs in the body usually have from 1 to 2 pieces, but there are 20 deciduous tooth and 32 permanent tooth. If tooth decay is not treated. It will cause pulp and periapex imflamation and the final result is early tooth extraction. That causes dysfution in chewing, affects total health, causes wrong position tooth and bad time of dentists as well as patients. So that prevention tooth decay and it's complication is very importion.