Comparative Analysis of the Mechanical, Surface, and Dimensional Properties of 3D-Printed Aligners: Influence of Printer Type and Nitrogen-Assisted Post-Curing

Abstract

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&apos;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.