Microstructure-Dependent Rotational Wear of Dental Glass-Ceramics Under Low Humidity

Background: The wear resistance of modern commercial glass-ceramic materials used in dental prostheses was investigated under cyclic contact conditions that included a rotational component. This loading mode has been largely overlooked in conventional in vitro wear testing, yet may be clinically relevant in patients with parafunctional conditions such as bruxism. Methods: Rotational loading was applied using an all-electric testing machine equipped with a biaxial actuator. Loading cycles combined a normal load (50 N) and a rotation (30°), at a frequency of 1 Hz. Microstructure and damage were characterized using advanced microscopy. Results: Rotational loading induced substantial damage across this class of materials, including the formation of glassy tribolayers with limited protective capability under the low-humidity conditions examined. Significant microstructure-dependent variations in wear volume were observed, with specific wear rates indicating severe wear (SWR above 10^-6 mm³/N·m threshold) in three of the five materials tested. Lithium disilicate glass-ceramics, characterized by a high fraction of elongated reinforcement crystals, exhibited the greatest resistance to damage, whereas leucite-based glass-ceramics showed the lowest. The dominant wear mechanisms were plastic-deformation-induced grooving and fracture-driven chipping. The findings are interpreted within established wear models for brittle materials (Archard and fracture-based) and supported by numerical simulations of stress fields across multiple length scales. Implications: The results provide mechanistic insight into rotational wear damage in glass-ceramic systems, a material class particularly susceptible to such loading, and inform strategies for material selection and microstructural design aimed at improving prosthetic durability.