EFFECTS OF THERMOCYCLING AND PH ON ULTRASTRUCTURES CHARACTERISTICS OF STAINLESS STEEL ARCHWIRES

Aim and Background. There are certain controversies about different changes in surface roughness and stiffness of stainless steel (SS) wires; also, the effects of thermocycling and saliva PH on the surface and mechanical properties of these orthodontics archwires. In the present study, the effects of thermocycling and saliva PH on the surface and mechanical properties of SS wires in Metallurgical Laboratory of Shiraz University during 2016-2017 were investigated. Method and materials. 5cm pieces of 0.016inch SS wires from Ormco Company were placed in a glassed-tube enclosed by borosilicate. The wires were randomly divided into groups 1, deepening in artificial saliva (PH 7.4), consisted of subgroups 1 and 2 and the second group with wires placed in the ascorbic acid contained artificial saliva (PH 4.5) consisted of subgroups 3 and 4 and each subgroup contained 10 pieces. 500 cycles of thermocycling in the 5 to 55 degrees C water were only applied to the subgroups 2 and 4. Surface and mechanical properties of SS wires were evaluated by Instron (Tensile Machine, Finland) and its roughness was measured by AFM machine. Finally, the data was analyzed using ANOVA. Results. A total of 40 samples in four groups based on different PH and presence/absence of thermocycling were evaluated. The most surface roughness was 0.15 +/- 0.02 mu m/Ra in PH 4.5 and presence of thermocycling. The lowest surface roughness was 0.06 +/- 0.009 mu m/Ra in PH 7.4 without thermocycling (P < 0.001). The maximum amount of stiffness was 24.6 +/- 1.4g/mm(2) in PH 7.4 without thermocycling and the lowest amount of it was 012.5 +/- 0.9g/mm(2) in PH 4.5 with the presence of thermocycling (P < 0.001). Conclusion. It seems that the lowest effects on the surface and mechanical properties of SS wires were induced in PH 7.4 without thermocycling.