Effect of Master Apical File Size and Taper on Irrigation and Cleaning of the Apical Third of Curved Canals

Objective: canal preparation generates a substantial amount of debris and smear layer (sl). the size and taper of the master apical file (maf) affects on penetra-tion of irrigants and subsequently canal cleaning efficacy.the aim of this study was to evaluate the effect of maf size and taper on penetra-tion of irrigants to the apical third of curved mesiobuccal (mb) canals of mandi-bular first molars.materials and methods: eighty-nine human mandibular first molars were di-vided into one control group (n=5) without rotary instrumentation and 6 experi-mental 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).results: 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 re-moved 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).conclusion: based on this study, 30.06 may be considered as the minimum maf size for acceptable debridement.