Real-time dynamic torque values and axial forces during preparation of straight root canals using three different...

To assess the real-time dynamic torque values and axial forces during preparation of straight root canals using three different endodontic motors and hand preparation.

Sixty maxillary incisors were divided into four homogeneous groups (n = 15). After glide path establishment (size 20) the root canals were prepared to an apical size 40 using the rotary NiTi system F6 SkyTaper. Motors (DentaPort ZX OTR, EndoPilot and VDW.silver) were set to 'auto-torque-reverse' mode and DentaPort ZX was set to its specific OTR mode (optimum torque reverse). One group served as a control using manual balanced-force canal preparation with K-Flexofiles. Teeth were embedded in resin and fixed in a multi-component sensor measuring axial and torsional load during active instrumentation with 50 Hz. Preparation time was also recorded. Data were statistically analysed using the Kruskal-Wallis test.

The maximum axial forces (peak) and both peaks of dynamic clockwise and counter-clockwise torque did not differ significantly when using the three different motors despite different gear ratios and pre-settings. Only the VDW.silver motor exceeded the torque values during the use of 30 instruments (3.3%). The Morita OTR motor exceeded the maximum intrinsic torque set at 1.0 Ncm in approximately 53% of cases. The larger tapered F6 SkyTaper instruments (size 20, .06 taper and size 30, .06 taper) created significantly higher torque values (P < 0.0001). Manual instrumentation created significantly lower torque levels and higher axial values compared to rotary instrumentation (P < 0.0001) and was significantly more time consuming (P < 0.0001).

Manual preparation was associated with significantly lower torque peaks compared to rotary instrumentation. The three motors remained well within the safety torque values of the instruments.