Mechanical properties of 3D‐printed and milled composite resins for definitive restorations: An in vitro comparison of initial strength and fatigue behavior.

Objective: To evaluate the flexural strength and fatigue behavior of a novel 3D‐printed composite resin for definitive restorations. Materials and Methods: Fifty disc‐shaped specimens were manufactured from each of a nanohybrid composite resin (NHC), polymer‐infiltrated ceramic network (PICN), and 3D‐printed composite resin (3D) with CAD‐CAM technology. Biaxial flexural strength (σin) (n = 30 per group) and biaxial flexural fatigue strength (σff) (n = 20 per group) were measured using piston‐on‐three‐balls method, employing a staircase approach of 105 cycles. Weibull statistics, relative‐strength degradation calculations, and fractography were performed. The results were analyzed with 1‐way ANOVA and Games‐Howell post hoc test (α = 0.05). Results: Significant differences in σin and σff among the groups (p < 0.001) were detected. The NHC group provided the highest mean ± standard deviation σin and σff (237.3 ± 31.6 MPa and 141.3 ± 3.8 MPa), followed by the PICN (140.3 ± 12.9 MPa and 73.5 ± 9.9 MPa) and the 3D (83.6 ± 18.5 MPa and 37.4 ± 23.8 MPa) groups. The 3D group exhibited significantly lower Weibull modulus (m = 4.7) and up to 15% higher relative strength degradation with areas of nonhomogeneous microstructure as possible fracture origins. Conclusions: The 3D‐printed composite resin exhibited the lowest mechanical properties, where areas of nonhomogeneous microstructure developed during the mixing procedure served as potential fracture origins. Clinical Significance: The clinical indications of the investigated novel 3D‐printed composite resin should be limited to long‐term provisional restorations. A cautious procedure for mixing the components is crucial before the 3D‐printing process, since nonhomogeneous areas developed during the mixing could act as fracture origins. [ABSTRACT FROM AUTHOR]