Effects of nitrogen-assisted post-curing and layer thickness on the properties of a 3D-printed ceramic-reinforced composite resin for permanent crowns under different aging conditions: an in vitro study

3D printing protocols play a critical role in determining the mechanical and physical properties of resin materials, with potential implications for their longevity and the clinical durability of prosthetic restorations. The present study aimed to evaluate the effects of layer thickness and nitrogen-assisted post-curing conditions on water sorption, solubility, surface roughness, and flexural strength of a 3D-printed ceramic-reinforced composite resin (CRC) for permanent crown restorations under two different aging conditions. A total of 120 disc-shaped specimens were fabricated from VarseoSmile TriniQ (BEGO GmbH & Co. KG, Germany) using two layer thicknesses (50 μm and 100 μm) and three post-curing conditions (2000, 4000, and 8000 flashes) with an Otoflash G171 unit under nitrogen atmosphere. Following post-curing, specimens were assigned to either 24 h distilled water storage (Group 1) or thermal aging for 5000 cycles at 5–55 °C (Group 2). Water sorption and solubility, surface roughness (SR), surface morphology, and flexural strength (FS) were evaluated in both groups. Data were analysed using two-way ANOVA with Bonferroni post hoc tests (α = 0.05). Neither layer thickness nor post-curing conditions significantly affected water sorption or solubility ( P > 0.05). Surface roughness was lowest at 4000 flashes for both layer thicknesses regardless of aging, with 50 µm specimens exhibiting lower values than 100 µm specimens at higher post-curing levels. Flexural strength was significantly influenced by post-curing conditions, with specimens post-cured at 2000 flashes showing lower values than those post-cured at 4000 and 8000 flashes ( P < 0.05). No significant differences were observed between the two aging groups in water sorption or flexural strength; however, surface roughness was significantly higher in the thermally aged group for 100 µm specimens post-cured at 2000 flashes (P < 0.05).” The physical and mechanical performance of the tested 3D-printed CRC was primarily influenced by post-curing conditions and layer thickness, regardless of aging conditions. Insufficient post-curing (2000 flashes) resulted in suboptimal surface and mechanical properties, while 4000 flashes provided the most favorable overall performance among the tested conditions. Within the limitations of this in vitro study, these findings highlight the importance of adequate post-curing for achieving favorable physical and mechanical properties of 3D-printed CRC restorations.