Impact of Different Cleaning Protocols on the Optical and Morphological Properties of 3D-Printed Aligners After In Vitro Aging

In-house printing of clear aligners (CAs) may represent a new revolution in CA therapy, providing a solution for the several limitations associated with indirect manufacturing. This study compared the changes in surface roughness and light transmittance (T%) of directly printed (DP) and thermoformed (TF) CAs after exposure to <i>in vitro</i> aging and different cleaning methods.A total of 48 aligners were fabricated using either multilayer thermoplastic polyurethane (CA Pro + , Scheu Dental; Iserlohn, Germany) or direct three-dimensional-printed resin (Tera Harz TC-85, Graphy; Seoul, Korea). CAs were aged <i>in vitro</i> (thermocycling and artificial saliva) and cleaned for 14 days with the following methods: Polident tablets, an electric toothbrush, Pril dish soap, an ultrasonic cleaning machine, and distilled water. Subsequently, alterations in surface roughness and T% were investigated using atomic force microscopy and spectrophotometry, respectively. This study was conducted from January to July 2025 at the Department of Orthodontics, College of Dentistry, University of Baghdad, Baghdad, Iraq, with additional laboratory work at the University of Technology/Ministry of Science and Technology.Data analysis included descriptive statistics, independent <i>t</i>-tests, one-way analysis of variance, and post hoc tests (Tukey's honestly significant difference or Games-Howell).Compared with the DP aligners, the TF aligners presented greater T% under all conditions, with the highest T% in the as-received condition. The TF and DP aligners showed the lowest T% in ultrasonic cleaning and control conditions, respectively. When excluding the as-received group, most cleaning methods showed statistically significant differences in T%. The surface roughness of the TF aligners was consistently lower than that of the DP aligners, with significant differences observed between the Polident and control groups.Cleaning methods altered the optical and morphological properties of both aligners. Customized cleaning methods are required for CAs.