Determining cutting efficiency of nickel-titanium coronal flaring instruments used in lateral action.

Aim To develop a method to evaluate the cutting behaviour of nickel-titanium ( Ni Ti) coronal flaring instruments. Methodology Bio Ra Ce BR0 ( BR), Hy Flex CM 1 ( HY), Pro File OS No. 2 ( PF) and Pro Taper Sx ( PT) instruments were used in simulated coronal flaring using a lateral action against bovine dentine blocks, at 250 and 500 rpm. Cutting efficiency was assessed by three methods: first, areas of notches produced by instruments were directly measured under a stereomicroscope. Second, dentine specimens were then analysed by surface profilometry to determine the maximum cutting depth and finally by microcomputed tomography to assess the volume of removed dentine. Data were compared using parametric tests with the significance level set at 0.05. Results For all three methods, HY and PF were the most and the least cutting-efficient instruments, respectively ( P < 0.05). Significant differences were detected between 250 and 500 rpm for HY and PT (area); for BR, HY and PT (depth); and for BR and HY (volume). There were strong positive correlations between the results obtained with those three different methods with r-values ranging from 0.81 to 0.92. Conclusion Measuring the amount of material removed in a specific time under stereomicroscopy is a simple and rational way to assess the cutting behaviour of Ni Ti rotary instruments in lateral action. Hy Flex, manufactured with thermomechanically treated Ni Ti wire, was the most efficient instrument, and increased rotational speed was associated with increased cutting efficiency. [ABSTRACT FROM AUTHOR]