Effects of cleaning protocols on the material properties of clear aligners and retainers: A systematic review

Clear aligners and retainers are widely used in contemporary orthodontics because of their esthetic appearance, removability, and patient-centered advantages. However, repeated exposure to dietary pigments and cleaning procedures may alter their optical, surface, mechanical, and chemical properties, potentially affecting appliance appearance, hygiene, and performance. This systematic review evaluated changes in the material properties of clear aligners and retainers following different cleaning protocols. Electronic searches were performed in PubMed, Scopus, LILACS, and the Cochrane Library from inception to February 28, 2026. Twenty studies were included, comprising 18 in vitro studies and 2 randomized clinical crossover studies. Cleaning protocols were categorized as mechanical, chemical, sonic or ultrasonic, and combined approaches. Optical and surface properties were the most frequently assessed outcomes, whereas evidence regarding mechanical properties, water absorption or mass change, and chemical composition remained limited. Across studies, the magnitude and direction of material changes varied according to appliance material, manufacturing method, cleaning modality, exposure duration, and outcome measurement. Mechanical brushing, particularly with toothpaste, was frequently associated with surface alteration, whereas chemical cleaning produced material- and exposure-dependent effects. Evidence regarding sonic or ultrasonic cleaning and directly printed aligners remained limited. Because most available evidence was derived from heterogeneous in vitro studies, no specific cleaning protocol can currently be considered universally optimal or supported by sufficient clinical evidence for routine recommendation. Future studies should adopt standardized designs, incorporate clinically relevant intraoral simulations, integrate biological and material outcomes, and further investigate additive manufacturing-related factors, particularly through adequately powered prospective clinical studies with standardized outcome measures.