Effect Of TiN Coating On Cyclic Fatigue Fracture Resistance Of Nickel-Titanium Endodontic Instruments In A Vitro Study

Objective: The purpose of this study was to test the effect of the magnetron sputtering Ti N coating on cycle fatigue resistance of KV4 rotary Ni Ti endodontic instruments,and to discuss whether the cycle fatigue resistance of Ni Ti instruments after Ti N coating was improving.Methods: A total of 80 KV4 rotary Ni Ti endodontic instruments(0.04 taper,25mm)were selected,and randomly divided in group A and group B.A and B were divided into two sub-groups:A1,A2,B1,B2.A1:20 instruments of 20 type,and Group A2: 20 instruments of 30 type;Group B1:20 instruments of 20 type and Group B2:20instruments of 30 type.A homogeneous layer of 0.6 ?m was deposited on the surface of group A but group B did not do any processing.Scanning electron microscopes(SEM)were used to examine surface morphology of Ni Ti instruments with and without coating.All instruments were test for resistance to cyclic fatigue failure inside copper artificial canal with a 60°angle of curvature and 5 mm radius of curvature.Recording the time to fracture from the start of the test until the moment of file breakage and the length of the fractured tip for each instrument.The NCF was calculated according to the rotating speed and fracture time.Results:1.Comparing group A1 with group B1,group A2 with group B2,cycle fatigue resistance of Ni Ti instruments with Ti N coating was significantly higher than Ni Ti instruments without Ti N coating.The difference was statistically significant(P < 0.05).No matter in the group of coating or non-coating,with the increase of the instruments type,cycle fatigue resistance was decreased.The difference was statistically significant(P < 0.05).However,there was no statistical significance(P>0.05)in the length of the fractured tip of 4 groups.2.The surface morphology of group A and group B was observed under low and high power SEM before the treatment,,and the surface of uncoated instruments was found with irregular cutting marks such as cracks.However,the surface of the coating instruments was smooth,without obvious cutting marks,showing a more homogeneous punctiform structure.After the cyclic fatigue test,the fatigue cracks of the two sets of instruments both were found to be originated from the surface of the instruments,and the crack was extended to the center of instruments.The fatigue lines and dimples on behalf of typical ductile fracture appeared.However,in addition to the main fatigue striations,there were relatively more fatigue lines on the surface of the uncoated instrument than coated instrument.Conclusion:The cycle fatigue resistance of KV4 rotary Ni Ti endodontic instruments had been improved remarkably after the magnetron sputtering Ti N coating.