Evaluation of In-Vivo Aging of 3D printed Orthodontic Aligners

Clear aligner therapy has revolutionized orthodontics, offering aesthetic and patient-friendly treatment options. While traditional vacuum thermoforming methods are widely used, direct 3D printing offers a promising alternative. This study proposes a novel, integrated measurement approach to evaluate the chemical stability of 3D-printed aligners fabricated using Tera Harz TC-85 resin after exposure to the oral environment. Combining Raman spectroscopy, X-ray diffraction (XRD), and optical microscopy, this study investigates morphological and chemical changes in the material after 7 and 14 days of in-vivo oral exposure. Raman spectroscopy analysis revealed remarkable chemical stability, with no significant compositional changes observed after two weeks of exposure. Characteristic peaks of polyurethane-based materials were identified, confirming material homogeneity across measurement points. Furthermore, Principal Component Analysis (PCA) of the Raman spectroscopy data revealed no significant spectral variations over time. The stability of the material's crystalline structure, verified by XRD, further supports the resilience of 3D-printed aligners under intraoral conditions. However, optical microscopic analysis revealed localized surface wear, suggesting potential alterations in mechanical properties over time. Wear patterns correlated with masticatory forces, emphasizing patient-specific variations. This measurement campaign solidifies direct 3D printing as a reliable aligner production method, and provides valuable insights into the long-term behavior of this kind of aligners, paving the way for optimizing their design and manufacturing for enhanced clinical outcomes.