Influence of deep dry cryogenic treatment on cutting efficiency and wear resistance of nickel-titanium rotary endodontic instruments.

This study tested the effect of cryogenic treatment on nickel-titanium (NiTi) endodontic instruments. Ten rotary NiTi instruments (ProFile 30, 0.06; Dentsply Maillefer Instruments SA, Baillegues, Switzerland)) were subjected to deep dry cryogenic treatment at liquid nitrogen temperature (-185 degrees C) (group A) and compared with that of nontreated instruments (group B). Root canals of 30 extracted permanent mandibular premolars were prepared to size 25 using ProFile 0.04 taper rotary NiTi instruments. Each instrument was used in 4 root canals for a total of 240 seconds. Cutting efficiency in rotary motion was assessed from weight loss of tooth samples after instrumentation. Wear resistance was assessed from surface defects on cutting heads pre- and postinstrumentation using scanning electron microscope. The weight loss was significantly higher in group A (p < 0.05, Student t test). The presence of surface defects after use was higher in group B. Deep dry cryogenic treatment increases the cutting efficiency significantly but not the wear resistance.