Comparison of Flexural Strength of Conventional Nanohybrid Composite Resins vs. 3D-Printed Resins for Definitive Restorations. In Vitro Study

Objective: To compare the flexural strength of conventional nanohybrid composite resin and 3D-printed resin used as definitive materials before and after thermocycling. Methodology: Type of research - experimental, In vitro, comparative. A total of 90 specimens were fabricated, divided into two groups of 45 samples each: conventional nanohybrid composite resin and 3D-printed resin. The study established the formation of four groups: Group A-1: Conventional nanohybrid composite resin without thermocycling (n=22), Group A-2: Conventional nanohybrid composite resin + 5000 thermocycling cycles (n=23), Group B-1: 3D-printed resin without thermocycling (n=22), and Group B-2: 3D-printed resin + 5000 thermocycling cycles (n=23). The specimens were fabricated following ISO 4049 standards (bars of 25x2x2mm). The conventional resins were prepared on a stainless steel matrix for subsequent polymerization, while the 3D-printed resins were designed using software. The samples underwent polishing, thermocycling, and calibration. The four groups were subjected to loads using a universal testing machine (Universidad de las Fuerzas Armadas, Materials Mechanics Laboratory) to measure flexural strength and compare the results. The results were analyzed using normality and homogeneity tests, specifically the Shapiro-Wilk test, which determined that the values were not normally distributed. Consequently, the non-parametric Kruskal-Wallis test was applied to compare the study variables. Results: Among the four groups subjected to load testing using the universal testing machine, the conventional nanohybrid composite resins without thermocycling showed an average flexural strength of 151.22±6.89 MPa, followed by thermocycled conventional nanohybrid composite resins with 103.56±7.13 MPa, 3D-printed resins without thermocycling with 96.85±6.52 MPa, and finally, thermocycled 3D-printed resins with 86.77±2.60 MPa. Conclusions: The conventional nanohybrid composite resin that was not subjected to thermocycling exhibited the highest flexural strength, with an average of 151.22 MPa, compared to the other groups, whose values were significantly lower. However, the thermocycled conventional nanohybrid composite resin and the non-thermocycled 3D- printed resin did not present statistically significant differences