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

Abstract

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. Specimens of a specific geometry (N = 720) were 3D printed from two resins for permanent applications (VAR=Varseo Smile Crown^plus, BEGO Medical; CRO= Crowntec, Saremco Dental), and one resin for temporary applications (FRE=Freeprint temp, Detax). They underwent five PP's, divided into three LED-groups (PP 1: 385 nm, 76 mW/cm², 180 s; PP 2: 400 nm, 77 mW/cm², 180 s; PP 3: 460 nm, 49 mW/cm², 180 s) and two flash curing groups (PP 4: 37 mW/cm², ten flashes per second, pulse duration 100 μs, curing period 2000 flashes/200 ms; PP 5: 90 mW/cm², ten flashes per second, pulse duration 100 μs, curing period 2000 flashes/200 ms). 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). 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. 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.