Mechanical Performance of 3D-Printed Resin Materials for Endocrown Restorations: A Comparative Evaluation of Fracture Resistance, Weibull Analysis, and Experimental Fracture Toughness.

Background and Objectives: Three-dimensional printing is increasingly used to fabricate dental restorations; however, limited evidence is available on the mechanical performance and fracture behavior of printable resin materials used for endocrown restorations. Fracture load alone may not fully describe material performance, particularly when brittle or defect-sensitive failure occurs. This in vitro study aimed to compare the fracture resistance, Weibull parameters, experimental Mode I fracture toughness parameter, and failure patterns of three 3D-printed resin materials used for endocrown restorations. Materials and Methods: Thirty anatomically identical molar replicas were produced from a single prepared tooth model and restored with endocrowns fabricated from NextDent C&B MFH (NextDent B.V., Soesterberg, The Netherlands), SprintRay Crown (SprintRay Inc., Los Angeles, CA, USA), and BEGO VarseoSmile Crown Plus (BEGO GmbH & Co. KG, Bremen, Germany) (n = 10/group). The restorations were cemented and subjected to compressive loading until fracture. Maximum fracture force values were analyzed using Welch's ANOVA and Weibull statistics. In parallel, single-edge-notched bend (SENB) specimens were fabricated from the same materials and tested using an ASTM D5045-based configuration to calculate an experimental Mode I fracture toughness parameter. Representative fractured crowns and standardized specimens were examined using stereomicroscopy to assess visible failure morphology. Results: No statistically significant difference in maximum fracture force was found among the three materials (Welch's ANOVA, p = 0.217). The mean fracture force values were 862.37 N for NextDent C&B MFH, 804.37 N for SprintRay Crown, and 699.43 N for BEGO VarseoSmile Crown Plus. In the complementary analyses, BEGO VarseoSmile Crown Plus showed the highest Weibull modulus (m = 9.36), indicating a narrower distribution of fracture values, and the highest mean experimental Mode I fracture toughness parameter (5.250 MPa·m0.5) under the present experimental conditions. Qualitative stereomicroscopic analysis revealed material-dependent visible failure patterns: SprintRay Crown exhibited more extensive fragmentation, whereas BEGO VarseoSmile Crown Plus showed a more defined visible fracture pattern with less secondary fragmentation. Conclusions: Fracture load alone was insufficient to characterize the mechanical behavior of the tested materials fully. Weibull parameters, the experimental fracture toughness parameter, and failure morphology provided complementary information and should be considered when evaluating 3D-printed resin materials for endocrown restorations.