ObjectiveThe objective of this study was to compare the resistance to sliding of aesthetic orthodontic coated wires after prolonged water immersion for up to 4 weeks.Setting and Sample PopulationAn in vitro study of commercially available orthodontic appliances.Materials and MethodsAesthetic coated stainless‐steel wires (Parylene‐coated, epoxy‐coated and Teflon‐coated) (0.019” × 0.025”) and an uncoated control were immersed in distilled‐deionized water for zero, two or four weeks at 37°C and then were subjected to resistance‐to‐sliding tests through a three‐bracket system of sapphire ceramic brackets (0.022” × 0.028” slot) and clear‐coloured elastic ligatures at a contact angle of 0° or 3°. Maximal and average resistance to sliding was analysed by a three‐way analysis of variance, two general linear models and a post hoc Tukey's honest significant difference test.ResultsWater immersion time, contact angle, wire group and their interactions had statistically significant effects on the resistance to sliding of tested orthodontic wires. Various coated wires had distinct timely changes in the maximal and average resistance to sliding after water immersion for 2 to 4 weeks. When compared to the uncoated control in most of the experimental conditions, epoxy‐coated wires had lower or non‐significant differences in resistance to sliding, while Parylene‐coated wire had higher resistances.ConclusionsProlonged water immersion for weeks alters the resistance to sliding of aesthetic orthodontic wires coated with Parylene, epoxy or Teflon. Based on their resistance to sliding, different designs in orthodontic biomechanics should be considered for the different aesthetic orthodontic coated wires.