Aim: The aim of the study was to investigate the relationship between final apical preparation size and smear layer removal in the apical third using conventional irrigation in mandibular bicuspids.
Methodology: Sixty-six extracted human mandibular bicuspids with comparable root canal morphology were divided equally into 5 experimental groups and a control group (n = 11). Based on their experimental group, samples were instrumented up to size 25, 30, 35, 40, or 45 with 0.04 taper using 2.5 % sodium hypochlorite (NaOCl) as the irrigant. Final irrigation was performed with 17% EDTA followed by 2.5% NaOCl. The control group was instrumented up to size 45/.04 and irrigated with distilled water. Samples were sectioned bucco-lingually and qualitatively evaluated under SEM for efficacy in smear layer removal. Kruskal-Wallis
and the Mann-Whitney U tests were employed for statistical analysis.
Results: Statistical analysis revealed comparable removal of smear layer in the coronal and middle thirds of all experimental samples regardless of grouping. Removal of smear layer in the apical third was significantly improved (p<0.05) when using file size larger than 35. There was no significant difference between 40/.04 and 45/.04.
Conclusions: Under the conditions of this study, using conventional irrigation, Apical enlargement more than size 35/.04 is essential to enhance removal of smear layer at the apical third.