Purpose: To evaluate the effect of different apical preparation sizes on the outcome of primary root canal treatment in mandibular first molars.
•n: 129 patients evaluating only Mandibular 1st molars with prespecified criteria
•1 operator performing the primary RCT using stepback tech with SS handfiles .02
•Divided to 5 experimental groups with a variable enlargement from the first apical binding file FABF n: 25 (GP.A: 2 sizes larger ; GP.B: 3 sizes larger; GP.C: 4 sizes larger; GP.D: 5 sizes larger; GP.E: 6 sizes larger)
• A statistically significant decrease in the PAI score in all of the groups. •GP.A had significantly lower PAI reduction compared to other groups and no significant difference was noted between other groups.
•The proportion of successfully healed cases increased with the increase in the apical preparation size with (A: 48%, B: 71%, C: 80%, D: 85%, and E: 92%)
•Significant difference in the proportion of healed/not healed cases only in GP. A Table.1.
•Enlarging the canal to 3 sizes larger than the FABF is adequate, any further increase in preparation size led to only an insignificant increase in the success rate.