Comparative Analysis of the Mechanical, Surface, and Dimensional Properties of <scp>3D</scp> ‐Printed Aligners: Influence of Printer Type and Nitrogen‐Assisted Post‐Curing

OBJECTIVES: This study aimed to compare the mechanical, surface, and dimensional properties of 3D-printed clear aligners (CA) fabricated using liquid crystal display (LCD) and digital light processing (DLP) 3D printing systems with nitrogen treatment. MATERIALS AND METHODS: Specimens were manufactured using LCD (Uniz NBEE) and DLP (Nextdent 5100) printers. Post-processing included residual resin removal and post-curing, with half of the specimens receiving nitrogen treatment. UV intensity was measured for each printer. Mechanical properties were assessed using tensile strength (n = 10), Shore D hardness (n = 8), and nano-indentation (n = 3). Optical and surface properties were assessed using translucency (n = 6) and surface roughness (n = 5). The accuracy of the CAs was assessed using root mean square deviation analysis (n = 4). Statistical analyses were performed using one-way ANOVA with Tukey's test and an independent samples t-test (p < 0.05). RESULTS: The LCD system showed more consistent UV intensity patterns during printing compared to the DLP system, as well as superior mechanical properties with higher tensile strength and Shore D hardness (p < 0.001). Nitrogen treatment significantly enhanced nano-indentation parameters, including Martens hardness and the elastic index in both LCD- and DLP-printed groups (p < 0.001). Both systems exhibited comparable translucency, surface roughness, and accuracy (p > 0.05). CONCLUSION: The choice of 3D printing systems significantly influenced CA properties. The LCD printing system demonstrated superior mechanical performance compared with the DLP system. In addition, nitrogen treatment significantly improved nano-indentation-derived mechanical properties, including Martens hardness and the elastic index. These findings suggest that the selection of the printing system and post-curing conditions may influence the mechanical performance of CAs.