Direct 3D printed aligners: Balancing clinical efficacy, biocompatibility and environmental sustainability - A critical mini-review.

This mini-review critically examines direct 3D printed aligners (DPAs) in orthodontics, focusing on their material properties, biocompatibility, clinical efficacy, and environmental impact based on studies from 2015 to 2025. DPAs demonstrate superior dimensional accuracy, uniform thickness, and improved force predictability compared to traditional thermoformed aligners, with clinical accuracy exceeding 64% for complex tooth movements and over 99% for transverse movements. Biocompatibility findings are mixed: while single-exposure assays often meet ISO 10993-5 standards, cumulative exposure models reveal progressive cytotoxicity linked to residual monomers such as urethane dimethacrylate (UDMA), emphasizing the importance of optimized post-curing protocols (typically 14–20 minutes under nitrogen atmosphere). Environmentally, DPAs reduce waste from physical models but may release microplastics (1–10 µm) during wear, raising concerns about systemic health effects and ecological sustainability, particularly given the lack of recycling programs for photopolymer aligners. The review highlights the need for standardized manufacturing protocols, long-term clinical studies, and development of biodegradable materials to balance clinical benefits with patient safety and environmental responsibility.