2Kang JA, Kim SK. Accuracies of seven different apex locators under various conditions [J] . Oral Surg Oral Med Oral Pathol Oral RadiolEndod, 2008, 106 (4): 57-62.
3Archer R, Reader A, Beck M, et al. An in vivo evaluation of the efficacy of ultrasound after step-back preparation in mandibular mo- lars [J] .J Endod, 1992, 18 (11)~ 549-552.
4Bobotis HG, Anderson RW, Pashley DH, et al. A microleakage study of temporary restorative materials used in endodontics [J] . J Endod, 1989, 15 (12): 569-572.
5Barthel CR, Strobach A, Briedigkeit H, et al. Leakage in roots coronally sealed with different temporary fillings [J] . J Endod, 1999, 25 (11): 731-734.
