effect of master apical file size and taper on irrigation and cleaning of the apical third of curved canals.

canal preparation generates a substantial amount of debris and smear layer (sl). the size and taper of the master apical file (maf) affects on penetration of irrigants and subsequently canal cleaning efficacy. the aim of this study was to evaluate the effect of maf size and taper on penetration of irrigants to the apical third of curved mesiobuccal (mb) canals of mandibular first molars.eighty-nine human mandibular first molars were divided into one control group (n=5) without rotary instrumentation and 6 experimental groups (n=14 each) that were prepared with the following race rotary files as maf: 25.04 (group1), 25.06 (group 2), 30.04 (group 3), 30.06 (group 4), 35.04 (group 5) and 35.06 (group 6). all the experimental groups were rinsed with 2 ml of 17 % edta followed by 2 ml of 5.25% naocl. debridement of the mb canals was evaluated using scanning electron microscope (sem). the data were statistically analyzed using kruskal-wallis and mann-whitney u tests (p<0.05).group 6 (maf=35.06) showed 100% acceptable debridement. this rate was 92.9% for maf=35.04. in group 4 (maf=30.06) smear layer (sl) was removed in the three-forth of the samples and debris was removed in 92.9% of them. acceptable debridement was not achieved in most samples of groups 1 and 2 (25.04 and 25.06, respectively) and the mentioned two groups had statistically significant difference in this respect with the other groups (p<0.05).based on this study, 30.06 may be considered as the minimum maf size for acceptable debridement.