Comparative Assessment of Color Stability in Four Commercial Clear Aligner Materials Exposed to Common Beverages: An In Vitro Study

Background Clear aligner therapy (CAT) has become a popular esthetic alternative to fixed orthodontic appliances, driven by advances in polymer science and digital manufacturing. However, staining and color instability remain significant clinical concerns, especially given patient non-compliance with recommended beverage restrictions. Limited comparative evidence exists regarding how different aligner polymers respond to common chromogenic beverages. Aim To evaluate and compare the color stability of four commercially available clear aligner materials, Invisalign® (polyurethane; Align Technology Inc., Tempe, Arizona, United States), ClearCorrect™ (polyethylene terephthalate glycol (PETG); Round Rock, Texas, United States), Illusion® (multilayer polyester blend; Laxmi Dental Ltd., Mumbai, India), and Graphy TC-85® (photocurable oligomer; Graphy Inc., Geumcheon-gu, Seoul, South Korea), following immersion in tea, coffee, cola, and red wine over a two-week period. Materials and methods This laboratory-based in vitro study used 40 aligner specimens (10 per brand), sectioned into standardized 10×10 mm samples. Specimens were randomly assigned to five immersion media (tea, coffee, cola, red wine, and distilled water). Color measurements (L*, a*, b*) were recorded at baseline, 24 hours, seven days, and 14 days using a VITA Easyshade® V (VITA Zahnfabrik H. Rauter GmbH & Co. KG, Germany) spectrophotometer. Total color change (ΔE) was calculated using the CIELAB formula. Data were analyzed using repeated-measures ANOVA with Tukey's post hoc tests (α=0.05). Results All aligners exhibited clinically acceptable baseline ΔE values (<3.3). Coffee and cola produced the highest discoloration across most materials. ClearCorrect™ and Illusion® demonstrated the greatest susceptibility, exceeding perceptible thresholds within 24 hours. Invisalign® showed moderate, beverage-independent staining, while Graphy TC-85® remained stable against acidic beverages but showed delayed tea-related discoloration. Time and beverage type significantly influenced ΔE values (p<0.001). Conclusion Color stability of clear aligners is strongly governed by polymer chemistry and beverage characteristics. PETG and multilayer polyester blends stain rapidly, polyurethane discolors moderately, and photocurable oligomers display beverage-specific behavior. Material-specific guidance and reinforced patient instructions are essential to maintain esthetic longevity of aligners.