RESUMEN
<p><b>OBJECTIVE</b>To compare the shaping ability of rotary ProTaper and Flexofile in simulated resin root canals.</p><p><b>METHODS</b>Forty simulated resin root canals were randomly assigned to two groups, one group for rotary ProTaper with crown-down technique and the other for Flexofile with balanced force technique. Change of working length and incidence of canal aberration and instruments failure were recorded. After preparation, the change of root canal curvature and the amount of resin removed at the inner and outer canal walls were measured with Image Pro Plus 5.0. The centring ability and total amount of resin removed were also assessed.</p><p><b>RESULTS</b>In the model of simulated resin canals, ProTaper instruments maintained working length better. Canals prepared with ProTaper instruments remained better curvature and showed fewer aberration compared with those prepared with Flexofile (P < 0.01). ProTaper instruments performed a better centring ability.</p><p><b>CONCLUSION</b>ProTaper instruments have a better shaping ability in simulated resin root canals.</p>