## 2 Materials and Methods  
All the finite element models were analyzed using the finite element method on the ANSYS Release 19.1 program. The model consisted of bone, soft tissue, interface gap, and maxillary denture with and without reinforcement, as shown in Figure 1. Teeth in the maxillary denture were not modeled in detail because only the stresses at the critical points of the denture were examined. During solid modeling, the surface coordinates of the maxillary denture base were taken from a real maxillary denture. The 'key points' were created from the coordinates to form the surface of the maxillary denture. These key points were merged by the 'line' command. Within the merged lines, the maxillary denture's upper surface area was created. The area obtained was transformed into a volumetric dimension. Unnecessary parts of the volume were removed and created volumes were bonded. The created model was solidified as a symmetrical half of the maxillary denture to reduce analysis time by reducing the number of elements. Material properties were entered into all individual volumes. Solid models were meshed with SOLID 186 elements in a controlled manner, which allowed for better geometric homogeneity of the elements and better discretization of the model by performing a mesh convergence study. The mesh consisted of a total of 39,170 nodes and 26,499 tetrahedral elements, as shown in Figure 2. SOLID 186 is a rigid element that contains 20 high-dimensional 3-dimensional nodes and exhibits three-dimensional deforming behavior. The element is defined by 20 nodes with three degrees of freedom per node. SOLID 186 is a type of element that  
Considering the boundary conditions of the skull and semi-model, boundary conditions were applied to the upper surface of the maxillary denture in the x, y, and z directions, and only in the x direction for the side surface shown in Figure 4, as the symmetrical half of the maxillary denture was modeled. The concentrated occlusal force of 230 N was applied, as shown in Figure 5[2,8,30]. Thermal loadings were considered as a steady state to simplify the problem. The initial temperature was taken as 36 \({}^{\circ}\)C, which is the human body temperature. Ambient temperatures of 36 \({}^{\circ}\)C, 0 \({}^{\circ}\)C, and 70 \({}^{\circ}\)C were applied to all the models. The effects of temperature variation on the mechanical properties of the materials were ignored to simplify the stress analysis. Figure 4: Boundary conditions of the maxillary denture-bone system. Figure 5: The applied occlusal singular force of 230 N.  
Figure 3: SOLID 186 homogeneous structural solid geometry. The properties of the reinforcement materials for a volume fraction of 55% were calculated approximately with the help of the literature [31]. Epoxy was considered a matrix material. The mechanical and thermal properties of each element on the model and seven different reinforcing elements are listed separately in Tables 1 and 2. The reinforcing materials were completely embedded into the maxillary denture. Seven different maxillary denture reinforcements made of CrCo, unidirectional and woven carbon/epoxy, unidirectional and woven glass/epoxy, and unidirectional and woven Kevlar/epoxy were modeled as volumes into the maxillary denture. Because of the irregularity of the model, the volume of reinforcement materials was meshed using SOLID 186 elements to simplify the reinforcement part, instead of modeling it as a multilayer composite. A gap was modeled instead of performing a contact analysis between the soft tissue and the denture, significantly reducing the calculation time compared to contact analysis. The Young's modulus of the gap was set at zero, but using this value alone caused abnormal large deformations between the soft tissue and the denture. Therefore, after analyzing the model with different values, the optimal value of the Young's modulus for the gap was selected as 0.07 MPa. Paths from the anterior to the posterior and the posterior to the lateral parts of the maxillary denture were defined.