Effects of three nickel titanium instrument systems on root canal geometry assessed by micro-computed tomography

To compare and evaluate the shaping ability of several nickel titanium instrument systems with different motions: two reciprocating single-file systems (Reciproc and WaveOne) and one continuous rotation/reciprocation full-sequence system [Twisted File (TF) Adaptive] using micro-computed tomography.

A total of forty-eight mesial canals of mandibular molars with two separate root canals and severe angles of curvature were selected. Canals were divided randomly to one of three experimental groups: group 1, reciprocating instrumentation with Reciproc R25, group 2, reciprocating with the Primary WaveOne file and group 3 'Adaptive Rotary Motion' with Twisted Files. Each group consisted of 16 root canals. Canals were scanned before and after root canal preparation, with a resolution of 20 μm using a micro-computed tomography system. The following parameters were assessed: changes in dentine volume, percentage of unshaped canal walls, degree of canal transportation and centring ability. Data were analysed using analysis of variance and Tukey's post hoc tests test to explore a significant difference in mean dentine removal, mean percentage of noninstrumented canals, mean degree of canal transportation and centring ratio between groups in the apical third and along the entire root canal. The level of significance was set at α = 0.05.

Preoperatively, there were no differences regarding root canal curvature and volume between experimental groups (P > 0.05). Overall instrumentation led to enlarged canal shapes with no evidence of preparation errors. None of the three groups was able to shape completely the root canal system. Mean dentine removal along the entire canal and in the apical third was significantly higher with Reciproc when compared with TF Adaptive and WaveOne (P = 0.013). Mean degree of canal transportation was significantly lower with TF Adaptive (P < 0.0001) followed by WaveOne and highest with Reciproc in the apical third and along the entire root canal.

None of the NiTi systems was able to instrument completely the entire root canal. Reciprocation and Adaptive Motions were found to cut dentine efficiently to full working length, with no procedural errors. The TF Adaptive system maintained the original canal anatomy with less canal transportation and better centring ability.