•Purpose: to determine whether apical enlargement of canals affected microbial reduction in patients undergoing root canal treatment.
•N= 7 articles.
•A PICO strategy was developed to identify previously published studies dealing with apical size of canal and microbial reduction.
•Inclusion criteria: üIn vivo human investigations from 1950 to 2014 which reported microbial reduction. üA comparison between different MAFS. üThe sample size was identified. ü The effect of enlargement on microbial reduction was measured as a primary objective. üQuantitative results were reported.
•Most highlighted Results
•4/7 articles suggested that apical enlargement significantly reduced the microbial load in canals.
•1/7 article reported a trend towards significant reduction in bioburden with a MAFS above 60 However, the difference between Profile 0.04 and LightSpeed rotary instruments that enlarged canals two sizes larger than (S2) was not significant.
•2/7 articles reported no difference in bacterial reduction with canal enlargement between sizes 25 and 40.
The best current available clinical evidence suggests that contemporary chemo-mechanical debridement techniques with canal enlargement techniques do not eliminate bacteria during root canal treatment at any size.