Evaluation of the mechanical properties of 3D printed interim resins polymerized with different postpolymerization units

STATEMENT OF PROBLEM: The effect of different postpolymerization units on the mechanical reliability and degree of conversion (DC) of 3-dimensional (3D) printed interim resins remains unclear, particularly when third-party units are used instead of manufacturer-recommended devices. PURPOSE: The purpose of this in vitro study was to evaluate the effects of 5 different postpolymerization units on the mechanical properties and DC of 5 commercially available 3D printed interim resins. MATERIAL AND METHODS: Five commercially available 3D printed dental resins were printed and postpolymerized using 5 different postpolymerization units (LC-3D Print Box, Tera Harz Cure, OneJet Cure+, ODS Cure Box, and ARUM UV Curing Machine). A total of 500 specimens were fabricated, including 250 bar-shaped specimens for flexural testing and 250 disk-shaped specimens for DC analysis. Statistical analysis included Kruskal-Wallis tests with Mann-Whitney U post hoc comparisons (Bonferroni correction) (α=.05). Reliability of mechanical performance was evaluated using Weibull analysis to calculate the Weibull modulus (m) and characteristic strength/modulus (σ₀) with 95% confidence intervals (CI). RESULTS: All resins exceeded the International Organization for Standardization (ISO) 10477 standard minimum flexural strength requirement (≥50 MPa). Flexural strength and modulus differed significantly depending on the resin-postpolymerization unit combination. The ODS Cure Box and Tera Harz Cure generally yielded higher flexural performance, whereas OneJet Cure+ produced the lowest values across materials. DC varied widely across polymerization conditions and showed no significant association with flexural strength or flexural modulus (P>.05). CONCLUSIONS: Mechanical properties varied across resin-postpolymerization unit combinations, with certain third-party units showing flexural performance comparable with that of manufacturer-recommended systems. Although the DC differed among polymerization conditions, the surface DC measured in this study did not show a significant association with flexural strength or modulus.