An in vitro comparison of canal preparation using two automated rotary nickel–titanium instrumentation techniques

AIM: The aim of this study was to compare the efficacy of root canal preparation using two automated rotary nickel-titanium instrumentation techniques with a double flared balanced forces hand preparation technique, using stainless steel files in extracted human teeth. METHODOLOGY: Sixty root canals in extracted human teeth were matched for curvature, length and diameter and divided evenly between three groups (group 1 = double flare using Flexofiles, group 2 = rotary nickel-titanium using McXIM instruments and group 3 = rotary nickel-titanium using Profile .04 Taper Series 29 instruments). The instruments were used according to the manufacturer's instructions in a torque controlled motor and handpiece (groups 2 and 3) and according to a predetermined procedure in group 1. A standardized radiographic technique using mercury as a contrast medium was used to evaluate the canal shape before and after preparation in the plane of maximum curvature. The pre- and postoperative radiographic images were compared against each other and with a predicted 'ideal preparation' calculated from a projection of the final instrument dimensions. The outcome measures were changes in canal dimensions as quantified by measuring the changes in the position of the inner and outer wall at 1 mm intervals. Alteration in canal curvature could be inferred by comparison with the ideal preparation. RESULTS: The degree of canal curvature did not influence the effectiveness of any of the techniques. The results showed no statistically significant differences in the outcome measures between the groups (two-way ANOVA). There were no significant differences in canal wall position changes at any level except the apical three, where significantly less change occurred in all groups (P = 1%). Instruments fractured in three canals, with acute curves in groups 2 and 3. CONCLUSIONS: Canal curvatures were equally and well maintained following preparation in all the groups, as long as the instrument did not fracture.