Esthetic stability of the TA-28 directly printed aligner: Insights into color change and surface wettability

This study aimed to evaluate the physical properties of directly 3-dimensional-printed clear aligners (DPA), fabricated from TA-28 resin (Graphy Inc, Seoul, Republic of Korea), subjected to thermal cycling, focusing on color stability and surface wettability as indicators of clinical performance and material durability.

Ninety disc-shaped specimens (15.0 × 2.0 mm) were fabricated using the manufacturer-recommended TA-28 resin (Graphy Inc). For color stability assessment, samples (n = 60) were immersed in distilled water, black tea, coffee, or red wine and evaluated at 1, 3, 7, and 14 days using a spectrophotometer based on the International Commission on Illumination L∗a∗b∗ and International Commission on Illumination color difference 2000 (ΔE00) systems. For surface wettability, specimens (n = 30) were subjected to thermal cycling at 5°C-55°C for 7 and 14 days, and the water contact angle was measured using the sessile drop method. Statistical analyses were conducted using the Kruskal-Wallis test for overall comparisons of nonparametric data, with post-hoc pairwise tests performed using the Mann-Whitney U test. For normally distributed variables, paired-samples t tests were applied. A significance level of P <0.05 was considered statistically meaningful.

Colorization tests revealed clinically unacceptable discoloration (ΔE₀₀ >2.25) in specimens immersed in tea, coffee, and red wine, with red wine producing the most severe changes (ΔE00 >30 at 14 days). A time-dependent increase in discoloration was observed across all staining solutions. Water contact angle values were consistently <90°, confirming a hydrophilic surface profile. Although values decreased after 7- and 14-day thermal cycling, the differences were not statistically significant (P = 0.143 and P = 0.599), indicating stable surface wettability over the aging period.

DPAs fabricated from TA-28 resin demonstrate hydrophilic surface characteristics and are highly susceptible to discoloration when exposed to pigmented beverages. These findings represent preliminary laboratory observations rather than clinical performance outcomes. Further studies simulating intraoral conditions, including mechanical wear and daily cleaning, are required to confirm the long-term esthetic stability of DPAs.