Mechanical Performance and Fracture Behavior of Fixed Dental Prostheses Under Bending Loads: An In Vitro Comparative Study

Aim: Fixed dental prostheses (FDPs) are increasingly fabricated from high-strength ceramic materials; however, their fracture behavior under flexurally dominated loading remains incompletely understood. This in vitro study aimed to compare the mechanical performance and fracture mechanisms of four FDP material systems under standardized bending conditions. Materials and Methods: Three-unit CAD/CAM-fabricated FDPs were produced from metal-ceramic (P1), zirconia-ceramic (P2), monolithic zirconia (P3), and monolithic lithium disilicate (P4) materials (n = 9 per group). Specimens were subjected to three-point bending until failure. Crack initiation load, maximum load, displacement, and stiffness were recorded, and fracture behavior was analyzed using stereomicroscopy, micro-computed tomography (μCT), and scanning electron microscopy (SEM). Results: Metal-ceramic FDPs (P1) exhibited the highest crack initiation load (0.89 kN) and maximum load (1.91 kN), with failure predominantly occurring through ceramic veneer delamination without complete framework fracture. Monolithic zirconia FDPs (P3) demonstrated the most brittle failure behavior, characterized by abrupt fracture and unstable crack propagation immediately after crack initiation. Zirconia-ceramic (P2) and lithium disilicate (P4) FDPs showed intermediate mechanical performance, with lithium disilicate exhibiting greater resistance to catastrophic failure (F_max = 0.94 kN) compared with zirconia–ceramic FDPs. Conclusions: These findings refine current assumptions regarding the mechanical reliability of monolithic zirconia FDPs under flexural loading and highlight the importance of fracture behavior, rather than peak strength alone, in material selection. Lithium disilicate and metal-ceramic systems exhibited more favorable damage-tolerant responses under static flexural loading. These findings should be interpreted within the limitations of this in vitro model and should not be directly extrapolated to long-term clinical performance.