Impact of different post-polymerization protocols on the material properties of three printed dental resins

OBJECTIVES: To investigate the influence of different post-polymerization protocols (PP) on polymerization depth and resultant degree of conversion (DC), Martens hardness (HM), flexural strength (FS) and elastic modulus (EM) of 3D-printed specimens with and without aging regimes. DC, HM, FS and EM were tested initially and after thermal cycling (10.000x, 5/55 °C) and within three different depths (0 mm, 2 mm, 4 mm). Data were analyzed with Kolmogorov-Smirnov, Kruskal-Wallis, Mann-Whitney-U test, Wilcoxon signed-rank test and Spearman's correlation (p < 0.05). RESULTS: PP 5 consistently showed high values for both aging regimes, while PP 3 presented the lowest results. Artificial aging increased the properties for most groups, some decreased. For DC 25/30 PP-groups and HM 27/30 PP-groups showed higher values for 0 mm depths in comparison with 2 mm and 4 mm depths. SIGNIFICANCE: Post-polymerization enhances the properties of the tested specimens intended for fixed dental prostheses (FDPs). PP 5 is recommended because it consistently resulted in highest DC, HM, FS, and EM across most groups, especially when combined with depths of 0 mm for DC and HM. Depths of 2 mm and 4 mm mostly resulted in lower values. Among LED groups, wavelengths of 385 nm and 400 nm are recommended for all materials, while wavelength of 460 nm seems not advisable.