Torsional testing of Canal Master U hand instruments.

Ten each of size 25, 30, 35, 40, and 45 Canal Master U hand instruments were tested for torsional failure and revolutions to failure. In addition, the point at which separation occurred was measured on the instrument shaft. An Instron 1125 machine was used for all torsion testing. The mean torque failure value for size 25 and 35 Canal Master U instruments exceeded the ADA specification No. 28 minimum values while sizes 30, 40, and 45 were below the ADA minimum average values. All Canal Master U averages for revolutions to failure exceeded the ADA minimums. Although size 25 was above the minimum average, due to a wide range of values, 5 of the 10 were below the ADA specification No. 28 values. The point of instrument separation was 0.325 to 1.575 mm behind the cutting head. Due to the structural design differences of endodontic files versus Canal Master U, it is suggested that an additional category of ADA specification be introduced for Canal Master endodontic instruments.