Coating stability of different esthetic NiTi archwires under high fluoride exposure

Methods: Ninety 0.016-inch esthetic nickel-titanium (NiTi) archwires were divided into three groups based on the type of coating (n=30): Group 1, rhodium-coated; Group 2, Teflon-coated; and Group 3, epoxy-coated. Each group was divided into three subgroups and kept in the following medium (n=10): A, artificial saliva with three ppm fluoride; B, plain artificial saliva; and C, as-received condition. In subgroups, A and B, 20 mm segments from NiTi archwires were immersed in test tubes containing the corresponding medium for 28 days. Afterwards, mechanical stress was applied to the samples of three groups using an electric toothbrush. The surface topography of the archwires in all subgroups was then examined by a stereomicroscope. Areas of coating loss were quantified using Capture 2.3 software. Statistical analysis was performed using two-way ANOVA, with a significance level of P<0.05.Results: ANOVA revealed no significant difference in coating loss among the study groups in the as-received condition (P=1.000) and after exposure to plain artificial saliva (P=0.651); however, in fluoride-containing artificial saliva, a significant difference was observed (P<0.01). Epoxy-coated wires had significantly greater coating loss than rhodium- and Teflon-coated wires (P<0.001). All groups showed a significantly higher coating loss in fluoride-containing artificial saliva than both plain artificial saliva and as-received subgroups (P<0.05).Conclusions: Epoxy-coated archwires exhibited the highest degradation in fluoride-containing artificial saliva, whereas Teflon- and rhodium-coated NiTi archwires showed better coating stability after fluoride exposure.