Staining and Cleaning Effects of Copolyester and Copolymer Retainer Materials

The increasing demand for aesthetics by all patients makes clear aligner therapy (CAT) and clear retainers in orthodontic treatment popular. The removable nature of clear retainers is often a benefit, allowing patients to remove the retainers to maintain good oral hygiene. However, long-term compliance is required of all post-orthodontic treatment patients and when patients become non-compliant, relapse can occur. Relapse is complicated and unpredictable. To prevent relapse, all patients should be treated as if they are at high-risk for relapse. Often, patients become non-compliant as the clear retainers become less clear, and therefore, less aesthetic. Thus, the need for research on how to maintain clear aligner translucency and color, while also maintaining the retainer properties and integrity, is needed. The objective of this study is to investigate the staining ability of different staining solutions on retainer materials and the effect of destaining agents on the light transmittance and color changes of two retainer materials, in vitro. This research focuses on the study of two retainer materials, copolyester (Essix ACE) and copolymer (Essix C+), stained with red wine, coffee, black tea, and distilled water followed by destaining with five cleaning materials, namely, hydrogen peroxide (H2O2), Invisalign® Cleaning Crystals, Retainer Brite, Polident denture cleaner, and Listerine mouthwash. The retainer materials were thermoformed over a custom stainless-steel block with disposable polymer molds rendering two surfaces, smooth and textured. The smooth surface mimics retainers made from plaster models and the textured surface mimics retainers made from 3D-printed models. The translucency and color changes of retainer material specimens were analyzed using specific spectrophotometers, and composition changes were evaluated by Raman Spectrometry before and after the 28-day staining and one-session destaining processes. During the destaining, one group of stained specimens were subjected to either ultrasonic or non-ultrasonic cleaning methods. The ∆ values were used to evaluate the change of color and translucency in each material from baseline to the end of the destaining process. Due to the non-normal distribution of the data analyzed by the Shapiro-Wilk test, the data was analyzed with non-parametric statistics, namely, Kruskal Wallis statistical and Mann-Whitney tests. Due to the differences in the innate characteristics of the individual materials, the outcome data were not compared between copolymer and copolyester. The results showed staining in both materials increased with exposure time. The most staining occurred at the end of staining (T3, 28 days) and the specimens were more susceptible to coffee and black tea staining. At the end of the staining period, the coffee and black tea staining solutions resulted in the most color change. After immersion in the destaining solutions, no statistically significant differences for light transmittance or color change were found between ultrasonic and non-ultrasonic cleaning groups. No major changes were noted among all staining solutions or destaining means. All cleaning solutions showed improved light transmittance. Both materials had statistically significant changes in translucency and color change on the textured surface. Qualitatively, no composition changes were observed in any groups at the end of destaining. The results from this study will contribute to an evidence-based approach for clinical guidance for long-term maintenance of clear retainer.