Residual Enamel Stress in a Mandibular First Molar Restored with a Ceromer Onlay Under Vertical and Oblique Loading: A Three-Dimensional Finite Element Analysis

Background/Objectives: Residual enamel fracture is a frequent complication of extensively prepared teeth. This finite element analysis (FEA) characterized stresses in enamel, dentin and restoration of a mandibular first molar restored with a ceromer onlay under vertical and oblique loading, and their sensitivity to boundary conditions and restoration stiffness. Methods: A single-geometry model from cone-beam computed tomography used linear elastic, isotropic materials and bonded interfaces. A static 698 N load was applied axially and at 30° with the root fixed 2 mm below the cervical limit of enamel. Mesh, support position, an elastic periodontal ligament (PDL) support and restoration modulus were varied. Maximum principal stress (σ1) was reported as peak, 99th percentile and proportion of nodes above published strengths. Results: Peak enamel σ1 was 51.0 MPa (vertical) and 167.6 MPa (oblique); 1.6% and 7.6% of enamel nodes reached 11.5 MPa, the lowest reported tensile strength. Peaks lay at the restoration margin and cervical edge, growing with mesh refinement. An elastic PDL support raised the enamel 99th percentile by 7% to 15%; restoration modulus changed it by +11% to −15%. Conclusions: Tensile concentrations are localized, increase with load obliquity and depend on the support conditions analyzed. Validation is required.