Advances in clear aligner therapy: comparative evaluation of the optical properties and bacterial adhesion of 3D direct-printed and thermoformed aligners

BACKGROUND: Clear aligner therapy is gaining traction owing to its esthetics and comfort. Although most aligners use thermoforming, 3D printing offers advantages such as higher accuracy and reduced waste. While literature on the properties of some 3D-printed aligner materials compared to thermoformed ones is available, a comprehensive study is currently lacking that compares all three materials (iLuxclear (LC), Graphy Clear Aligner (GY), and RightBio Clear Aligner (RD)) with thermoformed materials, particularly regarding optical and biofilm adhesion characteristics. METHODOLOGY: ) were evaluated after 7 and 14 days of aging in saliva, black tea, and coffee. Bacterial adhesion was quantified using Streptococcus mutans (S. mutans) at baseline and after 3 and 7 days. RESULTS: The 3D direct-printed aligners, particularly the LC group, exhibited increased surface morphology irregularities and significantly higher Ra values than the thermoformed materials; Ra increased after 45 days of immersion in artificial saliva across all groups. The thermoformed materials maintained stable color integrity, while the 3D-direct printed materials varied in performance. GY demonstrated a uniform surface structure, lower roughness, and the highest color stability, whereas LC and RD experienced significant discoloration. The RD group exhibited significantly higher S. mutans adhesion, whereas the thermoformed materials exhibited superior biofilm resistance. Notably, GY achieved comparable S. mutans adhesion to the thermoformed materials after a 7-day culture. CONCLUSIONS: Among the 3D direct printed aligners, GY achieved comparable surface and microbiological performance to conventional options. These findings underscore their potential for balancing esthetics, susceptibility to bacterial adhesion, and clinical performance in clear aligner therapy.