Fractographic analysis of 3D printed hybrid ceramic single crowns with different aging and post-curing times: an in-vitro study

Since increasing 3D-printed ceramics are being introduced to restorative dentistry, a critical evaluation of fabrication parameters for optimal clinical performance is necessary. While post-curing treatments have some influence on material properties, their impact on fracture resistance is not clear. This in vitro study aimed to systematically evaluate the effects of different post-curing times (10 vs. 20 min) and thermocycling aging (5,000 vs. 10,000 cycles) on the fracture resistance and failure modes of 3D-printed hybrid ceramic crowns (Saremco CrownTec). CAD software was utilized to create a standardized digital model of a mandibular first premolar crown. Eighty identical samples were produced with a high-precision 3D printer (Asiga Max UV) using Saremco Print Crowntec hybrid ceramic material. Samples were randomly allocated to two major groups according to post-curing time in a UV polymerization unit (10 min vs. 20 min). Each group was then assigned to two subgroups (n = 20 each) for thermocycling treatment (5,000 or 10,000 cycles between 5 °C and 55 °C). All crowns were adhesively cemented on PEEK dies with standardized preparation geometry. Fracture resistance testing was accomplished with a universal testing machine (Instron 5966) using a 5.6 mm steel ball indenter at 0.5 mm/min crosshead speed. Failure modes were examined using scanning electron microscopy SEM. Statistical analysis was conducted using two-way ANOVA (α = 0.05). The 10-minute post-cure group showed slightly greater mean fracture resistance (506.36 ± 58.44 N) than the 20-minute group (492.50 ± 76.06 N), but the difference was not statistically significant (p = 0.428). Thermocycling analysis showed that specimens that underwent 5,000 cycles had slightly better fracture resistance (510.00 ± 72.36 N) than those which underwent 10,000 cycles (488.26 ± 62.64 N), but the difference was also not statistically significant (p = 0.250). The failure patterns were reported and analyzed with SEM, based on extensions of failures on the axial surface. Although long post-curing times and thermocycling aging exhibited tendencies for decreased fracture resistance, the effects were not statistically significant under the parameters tested. Research in the future should examine the influence of various post-curing intensities and extended aging simulations to further support these results.