Effect of Intra-Aligner Bleaching on Nuvola® Clear Aligner Material During Prosthodontic Pretreatment: An Ex Vivo Thermomechanical and Infrared Spectroscopic Study

Clear aligners can be carriers of bleaching agents as pretreatment before orthodontic and prosthodontic treatment and therefore are exposed to the influence of the oral cavity and oxidizing agent. In this research, the effects of 14 days’ intra-aligner bleaching with 10% carbamide peroxide during clinical treatment on the thermomechanical behavior and infrared fingerprint of Nuvola® aligners were assessed. Five experimental groups were tested (six DMA specimens in each group): control (not used), 14 days wear without bleaching, and 14 days wear with bleaching for 3, 7, and 14 days. The onset glass transition temperature (Tg) was determined by dynamic mechanical analysis, and Fourier-transform infrared spectroscopy (FTIR) was applied for qualitative evaluation of the chemical fingerprint of PETG. Statistically higher Tg was found in bleached groups than in the control and wear-only groups, although the values differed only between 78.35 and 79.23 °C. No trend of changes depending on exposure duration was found. There were no shifts in FTIR peaks, no additional bands appeared, and no characteristic bands disappeared. Thus, bleaching caused a statistically significant but small Tg increase and did not alter the infrared fingerprint of PETG. Low-level chemical modification below the sensitivity of qualitative FTIR cannot be excluded.