Temperature rise on the surface of NiTi and stainless steel fractured instruments during ultrasonic removal.

AIM: To investigate the temperature rise induced by ultrasonic tips when activated against two types of fragments at two power-settings. METHODOLOGY: Twenty-four F2-ProTaper Universal rotary files and 36 stainless steel K-files, size 50, were sectioned at a point 5.5 mm from their tips. At specific power-settings, ET40D ultrasonic tips were activated against the peripheral surface of the fragment coronal part (1 mm) for 30 s with/without Air-Active function according to each group; (i) without Air-Active function at power-setting 1.5 against NiTi fragments, (ii) without Air-Active function at power-setting 1.5 against SS fragments, (iii) without Air-Active function at power-setting 3 against SS fragments, (iv) with Air-Active function at power-setting 3 against SS fragments, and (v) with Air-Active at power-setting 3 against NiTi fragments. Temperature rises were inspected at 15 and 30 s using the thermocouples. RESULTS: With no Air-Active function and power-setting 1.5, the temperature rises induced on NiTi fragments at 15 and 30 s (36.33 and 55.44 degrees C, respectively) were significantly greater than those induced on SS fragments at 15 and 30 s (26.08 and 35.27 degrees C, respectively) (P = 0.001 and <0.001, respectively). When ultrasonic tips were activated against SS fragments without Air-Active, the temperature rises induced by power-setting 3 at 15 and 30 s (35.25 and 45.32 degrees C, respectively) were significantly greater than those induced by power-setting 1.5 at the same intervals (26.08 and 35.27 degrees C, respectively) (P = 0.006 and 0.012, respectively). At 30 s, the overall temperature rise induced with Air-Active (25.56 degrees C) was significantly lower than that induced without Air-Active (45.34 degrees C) (P < 0.001). CONCLUSIONS: Lower power-settings and shorter application times are recommended when using ultrasonics for removal of NiTi fragments compared with SS ones. Air-Active function, as a coolant, is recommended when dealing with both types of fragments.