Biocompatibility of Direct 3D-Printed Clear Aligner Resins: A Comparative In Vitro Cytotoxicity Analysis

This study comparatively evaluated the mechanical properties of four commercially available, directly three-dimensional (3D) printed clear aligner materials by analyzing tensile behavior, flexural properties, and surface hardness.

Four direct-print clear aligner resins were included: CRS, LuxCreo, Rayform 4D clear aliner resin, and PowerResins clear smile resin. Specimens were fabricated according to the manufacturers' protocols with a standardized thickness of 0.70 mm and 50 m layer thickness in vertical orientation. Tensile (n = 5), three-point bending (n = 5), and Shore D hardness (n = 10) tests were performed at room temperature (23°C) at the accredited laboratories of TÜBTAK Marmara Research Center. Statistical analysis was performed using one-way analysis of variance followed by Sidak's multiple comparisons test (p < 0.05).

Significant differences were found among all materials for all tested parameters (p < 0.0001). PowerResins showed the highest elastic modulus (2187.7 ± 315.8 megapascals [MPa]), tensile strength (51.5 ± 2.9 MPa), flexural modulus (1609.7 ± 95.6 MPa), flexural strength (71.9 ± 2.9 MPa), and Shore D hardness (87.3 ± 0.9), indicating superior rigidity. LuxCreo demonstrated the highest elongation at break (118.4 ± 10.7%), suggesting greater flexibility and ductility. Rayform 4D showed intermediate mechanical behavior, whereas CRS generally exhibited lower flexural resistance.

Directly printed clear aligner materials exhibit significant variability in mechanical properties. PowerResins may be more suitable for cases requiring greater rigidity and force delivery, whereas LuxCreo may be preferable when flexibility and patient comfort are prioritized. Material selection should be based on specific orthodontic treatment objectives and clinical biomechanical requirements.