The shaping effect of the combination of two rotary nickel-titanium instruments in simulated S-shaped canals

This study aimed to analyze the ability of ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) combined with Hero642 (MicroMega, Besancon, France) to shape the simulated S-shaped canals. Thirty simulated canals with double curvatures, 30 degrees coronally and 20 degrees apically, were randomly divided into three groups and prepared with different instruments: ProTaper in group 1, Hero642 in group 2, and a combination of ProTaper and Hero642 in group 3. All canals were scanned pre- and postoperatively. Each postinstrumentation image was superimposed with the preoperative one in a computer. The amount of material removed from canal wall after every instrument was measured at 14 points. Statistical analysis was performed by using an analysis of variance test at alpha = 0.05. Canals prepared with rotary ProTaper were straightened progressively after the use of F1, and great transportation was created. Hero642 and the combination instruments maintained the original shape of canal with a little transportation. However, the taper of canals prepared with Hero642 was relatively poor.