5[4] Vire DE.Failure of Endodontically Treated Teeth:Classification and Evaluation.J Endo,1991，17:340
6[1] Masahiro, et al. Correlation between clinical symp toms and microorganisms isolated from root canals of teeth with periapical pathosis.J Endod ,1987,13:24
7[3] Benanat; FW, et al. Recall evaluation of iatrogenic root perforations repaired with amalgam and percha. J Endodon, 1986，12:161
