Comparative Evaluation of Surface Roughness of Direct-Printed 3D and Thermoformed Orthodontic Aligners: An Ex Vivo Study

Abstract

Background: Clear aligner therapy has become an integral component of contemporary orthodontics owing to its superior esthetics, patient comfort, and removability. The long-term clinical performance of aligners depends not only on their mechanical properties but also on their surface characteristics. Surface roughness influences bacterial adhesion, biofilm accumulation, optical transparency, and patient comfort. Recently introduced direct three-dimensional (3D)-printed aligners have eliminated the conventional thermoforming process; however, evidence regarding their surface integrity after intraoral use remains limited.

Objective: To compare the surface roughness characteristics of direct-printed 3D aligners and thermoformed orthodontic aligners before and after clinical intraoral use.

Materials and Methods: An ex vivo comparative study was conducted using three commercially available aligner materials: polyethylene terephthalate glycol-modified (PET-G; Erkodur), thermoplastic polyurethane (TPU; Zendura FLX), and directly printed aligners fabricated from Graphy TA-28 resin. Twenty aligners were included in each group. Surface roughness was evaluated before intraoral use (control) and after clinical use using a non-contact optical profilometer. The evaluated parameters included arithmetic mean height (Sa), root mean square height (Sq), maximum surface height (Sz), profile roughness (Ra), root mean square roughness (Rq), total profile height (Rt), valley void volume (Vvv), and core void volume (Vvc). Statistical analysis was performed using the Kruskal–Wallis test for intergroup comparisons and the Wilcoxon signed-rank test for intragroup comparisons. Statistical significance was established at p < 0.05.

Results: Significant differences in surface roughness were observed among the three aligner materials. Following intraoral use, PET-G and TPU aligners demonstrated a significant reduction in most surface roughness parameters, indicating a polishing effect produced by the oral environment. In contrast, direct-printed aligners exhibited significantly higher surface roughness values after clinical use, suggesting increased susceptibility to surface degradation. Intergroup comparisons revealed significantly greater roughness values in direct-printed aligners than in thermoformed materials.

Conclusion: Surface characteristics differed significantly between thermoformed and direct-printed aligners. Thermoformed PET-G and TPU aligners exhibited smoother surfaces after intraoral use, whereas direct-printed aligners demonstrated increased surface roughness that may favor plaque accumulation and biofilm formation. Further improvements in printing technology and resin formulation are required before direct-printed aligners can consistently achieve the surface quality of conventional thermoformed aligners.