Influence of thermal or chemical degradation on the frictional force of an experimental coated NiTi wire.

Objective: To evaluate the friction force in sliding systems composed of coated NiTi archwires, coated NiTi subjected to thermal cycling, and coated NiTi subjected to acid solution immersion, and compare them to NiTi and polymeric wires. The null hypothesis is that there will be no difference among the wires as to friction force.

Materials And Methods: Samples of NiTi (n  =  05), coated NiTi (n  =  15), and OPTIS (n  =  05) 0.016 inches in diameter and 50 mm long, in conjunction with Metafasix ligatures and saliva in InVu brackets, were submitted to friction testing. Among the 15 coated NiTi samples, 5 were submitted to thermal cycling for 3000 cycles; the other 5 samples were immersed in acid solution for 30 days. The results were statistically analyzed at P > .05 or P > .01. Microscopic analysis was performed in the coated NiTi wires before and after thermal cycling and acid solution immersion.

Results: The mean (± standard deviation) maximum friction force for NiTi, coated NiTi, and OPTIS was 105.20 ± (2.63); 99.65 ± (0.64); 59.76 ± (4.93) (P  =  .000), respectively. There was no significant difference in NiTi, coated NiTi, and acid-immersed coated NiTi (P > .05). Among the thermal-cycled or acid-immersed coated NiTi wires there was lower friction force in those undergoing thermal cycling (P  =  .001). The coated NiTi and the OPTIS presented homogeneous surfaces, whereas NiTi wires presented a heterogeneous surface. Fractures were observed in the coated NiTi wires that underwent thermal cycling.

Conclusion: OPTIS, thermal-cycled coated NiTi, coated NiTi, NiTi, and acid-immersed coated NiTi presented, respectively, increasing values of maximum friction force.