Rotary continuous and reciprocating single-file nickel-titanium instruments in the induction of dentinal cracks

Root canal preparation with a nickel-titanium (NiTi) rotary instrument may induce cracks in the root canal wall. This study sought to evaluate and compare the incidence of cracking in the root canal wall after root canal preparation using single-file NiTi rotary instruments with rotary continuous and reciprocating movements via micro-computed tomography (micro-CT) analysis. Thirty-two single root canal samples were randomly assigned into two groups-reciprocating instruments and rotary continuous instruments (n = 16 per group)-according to the system used for root canal preparation. The samples were scanned by high-resolution micro-CT imaging to evaluate for cracks before and after root canal preparation. Comparisons were analyzed statistically using Fisher's exact test. Post instrumentation cracks were detected in both the reciprocating group (12.5%) and rotary continuous group (25%) and there was no significant difference in the number of cracks between the two (P >.05). Cracks were most often found in the apical one-third of the root canal. Root canal preparation with single-file NiTi rotary continuous and reciprocating instruments can induce dentinal cracks in the root canal wall with no significant differences in the cracks induced between the two types of movement.