Shaping ability of ProTaper nickel-titanium files in simulated resin root canals

Aim To determine the shaping ability of ProTaper instruments in simulated root canals. Methodology Forty canals with four different shapes in terms of angle (20degrees and 40degrees) and position of curvature (straight section before curve: 8 and 12 mm) were enlarged according to the recommendations of the manufacturer with the finishing files F1, F2 and F3 to full working length. Preoperative and postoperative pictures, recorded using a digital camera, were superimposed and aberrations recorded. Measurements were carried out at five different points: at the canal orifice (O); half-way to the orifice in the straight section (HO); beginning of the curve (BC); apex of the curve (AC); end-point (EP). Results Ten instruments deformed (nine F3 and one S1, all in canals with straight section of 8 mm), one instrument fractured. There were significant differences between the various canal shapes for the amount of resin removed from the inner curve at all points (O: P < 0.05; HO: P = 0.001; BC, AC and EP: P < 0.001); and for the resin removed on the outer curve at points HO, AC and EP (P < 0.001). Mean transportation was towards the inner aspect of the curve in all canal types at points BC, towards the outer aspect at the end-point of preparation (EP) in all canals with 12 mm straight section. In 8 mm straight section canals, four danger zones were found; in 12 mm straight section canals three zips were present. The canal aberrations were produced following the use of the F2 and F3 instruments. There were no aberrations following the use of the F1 instrument. Conclusions Under the conditions of this study, ProTaper instruments performed acceptable tapered preparations in all canal types. When using F2 and F3 in curved canals, care should be taken to avoid excessive removal at the inner curve, leading to danger zones. In addition, care should also be taken to avoid deformation of the F3 instrument.