Evaluation of the root dentine cutting effectiveness of the HERO 642, HERO Apical and HERO Shaper rotary systems.

Different HERO rotary systems were evaluated by pre- and postoperative images of a cross-section of their mesiobuccal root thirds with a stereoscopic magnifier (45x). Fifty mesiobuccal canals of human mandibular first molars were divided into five groups: 1--HERO 642; 2--HERO 642 and HERO Apical; 3--HERO Shaper; 4--HERO Shaper and HERO Apical; 5--NitiFlex files. The perimeter of the canal was calculated using Image Tool software (UTHSCA). Final, post-instrumentation perimeters were compared by Kruskal-Wallis test (P = 0.05). The distribution of the values of the final canal perimeter for each instrumentation method was not statistically significant in any of the thirds (P = 0.174, cervical third; P = 0.874, middle third; and P = 0.631, apical third). An increase in canal perimeter was observed in all groups. In the cervical third the greatest increase was Group 5; in the middle third, Group 4, and in the apical third, Group 2.