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Comparative investigation of two rotary nickel-titanium instruments: ProTaper versus RaCe. Part 1. Shaping ability in simulated curved canals.

AIM
To compare the shaping ability of ProTaper with Reamer with Alternating Cutting Edges (RaCe) instruments. Part 1 of this two-part report describes the efficacy of these two nickel-titanium instruments in simulated curved root canals.


METHODOLOGY
Simulated canals with 28 degrees and 35 degrees curves in resin blocks were prepared with ProTaper and RaCe instruments using a crown-down preparation technique (n = 24 canals in each case). Pre- and postinstrumentation images were recorded, and assessment of canal shape was completed with a computer image analysis program. Material removal was measured at 20 measuring points, beginning 1 mm from the apex. Incidence of canal aberrations, preparation time, changes of working length and instrument failures were also recorded. The data were analysed statistically using the Mann-Whitney U-test or the chi-square test.


RESULTS
On average, canals prepared with RaCe instruments remained better centred compared with those enlarged with ProTaper files. Three RaCe instruments and two ProTaper files fractured during preparation (P > 0.05). Between both the canal types, RaCe was significantly faster (P < 0.001) than ProTaper and maintained working length significantly better (P < 0.05).


CONCLUSION
Both instruments prepared curved canals rapidly and were relatively safe. RaCe respected original canal curvature better than ProTaper, which tended to transport towards the outer aspect of the curve.