Phase Transformation Behavior and Resistance to Bending and Cyclic Fatigue of ProTaper Gold and ProTaper Universal...

The purpose of this study was to compare the flexibility and cyclic fatigue resistance of ProTaper Universal (PTU; Dentsply Tulsa Dental Specialities, Tulsa, OK) and ProTaper Gold (PTG; Dentsply Tulsa Dental Specialities, Tulsa, OK) instruments in relation to their phase transformation behavior.

Sizes S1, S2, F1, F2, and F3 of PTU and PTG instruments were subjected to rotational bending at a curvature of 40° and a radius of 6 mm. The number of cycles to fracture (NCF) was recorded. The fracture surface of all fragments was examined with a scanning electron microscope. Flexibility was determined by 45° bending tests according to the ISO 3630-1 specification. Unused and fractured instruments were examined by differential scanning calorimetry.

PTG had a cyclic fatigue resistance superior to PTU in all sizes (P < .001). The NCF of the nickel-titanium files of sizes S1 and S2 was significantly higher than those of sizes F1 to F3 (P < .001). No significant difference in the NCF of PTU instruments was detected between F1 and F2. The fractured files of both PTU and PTG showed the typical fracture pattern of fatigue failure. The bending load values were significantly lower for PTG than for PTU (P < .05). The differential scanning calorimetry analyses showed that each segment of the PTG instruments had a higher austenite finish temperature (50.1°C ± 1.7°C) than the PTU instruments (21.2°C ± 1.9°C) (P < .001). PTG instruments had a 2-stage transformation behavior. There was no significant difference in the austenite finish between unused files and instruments subjected to the fatigue process.

PTG files were significantly more flexible and resistant to fatigue than PTU files. PTG exhibited different phase transformation behavior than PTU, which may be attributed to the special heat treatment history of PTG instruments. PTG may be more suited for preparing canals with a more abrupt curvature.