Wear mechanisms and damage evolution of superelastic NiTi orthodontic archwires under coupled bending-sliding loading in simulated oral conditions

Nickel–titanium (NiTi) archwires are widely used in orthodontic applications due to their superelastic response and ability to deliver nearly constant forces. During clinical service, these components are subjected to repeated sliding, bending, and moderate temperature variations, which can promote progressive surface degradation. In this study, the influence of combined thermo-mechanical loading on the wear and damage behavior of commercial NiTi archwires was experimentally investigated under simulated oral conditions. Cyclic friction tests were performed in artificial saliva on circular and rectangular archwires at different temperatures, normal loads, and archwire deflection levels using a rotating tribometer. A bending device was employed to closely reproduce in-vivo conditions. After 12,000 sliding cycles, wear rates increased by ∼50% for the rectangular archwire in the active configuration and by about 60% when the normal load was raised to 13 N at 50 °C, compared with passive conditions at 2 N ( n = 3, p < 0.001). Increasing the test temperature above the austenite finish temperature ( A f ) led to a further decrease in wear resistance. Scanning electron microscopy analysis of the wear tracks revealed that abrasive and fatigue-assisted wear patterns were the dominant degradation mechanisms. Bending promoted localized deformation and surface cracking, contributing to reduced fatigue life. Cyclic friction in these regions further enhanced surface damage. These findings provide experimental insight into damage evolution in superelastic NiTi components under combined cyclic loading and moderate temperature variations, offering guidance for durability assessment of orthodontic archwires under service-like conditions.