Objective <p>To explore the influence of different inlay materials, depth, and width variations on stress distribution using the finite element method, and to provide a quantitative theoretical basis for the selection of clinical inlay restoration schemes.</p> Method <p>A three-dimensional finite element model of the mandibular first molar was established. The models were organized into four main groups based on the restorative material: Zirconia, Lithium Disilicate (LD), Gold Alloy (GA), and Resin-Based Ceramics (RBCs). Each material group was further divided into nine subgroups, simulating MOD inlay restorations with different preparation parameters: inlay depth (d = 2 mm, 4 mm, or 6 mm) and width (w = 2 mm, 4 mm, or 6 mm). A&#xa0;total of 36 groups of models were constructed. A vertical and oblique static load of 100 N was applied to the occlusal surface, and the distribution characteristics of the maximum principal stress (MPS) under different variable combinations were analyzed.</p> Results <p>The MPS of the four types of inlays were all concentrated on the stress-bearing contact surface and the bottom of the inlays. In terms of materials, under vertical loading,&#xa0;when d = 2 mm and w = 2 mm, the Zirconia group had the highest MPS (143.2 MPa), the RBCs group had the lowest (115.5 MPa), and the values of the LD group (127.9 MPa) and the GA group (128.3 MPa) were between the two.</p> Conclusion <p>According to this finite element study, the stress distribution is influenced by the complex interaction between the material properties and the geometry of the preparation. Moreover, the stress distribution of RBCs is more uniform than that of high-modulus materials. In clinical applications, the restorative materials and preparation parameters should be comprehensively selected according to the conditions of the affected teeth, and the long-term effects still need in-depth research.</p>