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

Abstract

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 (σ_in ) (n = 30 per group) and biaxial flexural fatigue strength (σ_ff ) (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 σ_in and σ_ff among the groups (p < 0.001) were detected. The NHC group provided the highest mean ± standard deviation σ_in and σ_ff (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.

Keywords: 3D-printed composite resins; Weibull; additive manufacturing; flexural fatigue strength; flexural strength; milled composite resins; staircase approach.