Stress distribution of inlay, onlay, and overlay restorations across materials: A finite element study

PURPOSE: We evaluated the stress distribution patterns in inlay, onlay, and overlay restorations fabricated from different CAD-CAM materials, including current 3D-printed resins and 3D-printed zirconia, under 300 N vertical loading using finite element analysis (FEA). METHODS: A 3D solid model of a mandibular first molar was generated based on standard anatomical dimensions. Fifteen finite element models were constructed by combining three preparation designs with five restorative materials. A static vertical load of 300 N was applied and distributed across the multipoint occlusal contacts to simulate physiological masticatory forces. The stress distribution was analyzed using the von Mises and Maximum Principal Stress criteria to evaluate both the restoration and the surrounding dental tissues. RESULTS: Restoration design and material stiffness significantly influenced stress distribution. Among the designs, the overlay preparations exhibited the most favorable biomechanical behavior, showing lower stress transmission to the tooth structure than inlay and onlay designs. Materials with a high elastic modulus (205.000 MPa LithaCon 3Y-210) demonstrated a stress-shielding effect, absorbing higher internal stress while protecting the underlying dentin. Conversely, low-modulus materials (4.030 MPa VarseoSmile Crown Plus) exhibited lower internal stress, but transferred higher stress loads to the tooth-restoration interface and dentin. CONCLUSIONS: The use of overlay designs combined with high-elastic modulus materials offers a biomechanically superior configuration for reinforcing compromised posterior teeth because this combination minimizes stress transmission to the remaining tooth structure. Although low-modulus materials reduce internal restoration stress, they require careful consideration because of the increased stress transfer to the dentin.