## 1 Introduction  
Teeth health loss is one of the biggest problems for human health and impairs patients' appearance, masticatory ability, speech etc. These functional disorders affect quality of life standards for patients. To resolve these unhealthy situations, partial or complete removable dentures are frequently utilized [1, 2]. Since the early 1940s, acrylic resin based on PMMA (polymethyl methacrylate) has been one of the materials routinely used in prosthetic dentistry [3, 4, 5, 6, 7, 8, 9, 10]. PMMA has been the material of choice due to its excellent appearance, stability in the oral environment, repairability, and ease of repair [4, 5, 7, 10, 11, 12, 13]. The mechanical weakness of the PMMA denture base material, in terms of low tensile and bending strength, remains an unresolved problem [2, 4, 6, 8, 14, 15, 16, 17, 18]. Midline fracture is the most common failure in maxillary and mandibular dentures [19]. Fractures of maxillary complete dentures are the most widespread denture failure [20]. To overcome these deficiencies, there are some ways that have been investigated to improve the strength of PMMA by reducing stress concentration and preventing mechanical weakness. In those investigations, researchers conducted studies on alternative materials to PMMA, chemical modification of PMMA, and the reinforcement of PMMA with fibers such as glass fiber, carbon fiber, Kevlar, and metal inserts [7, 9, 10, 21]. In many studies, different methods such as strain gauges [22], holography [23], photoelasticity [24], and finite element analysis have been used to determine the stress concentration and distribution of dentures. Since the strain gauge method measures strainsoccurring on the surface of dentures, it cannot measure stresses in reinforcement materials embedded in the dentures. Both photoelasticity and holography are optical methods and not appropriate for investigating the stress distribution of dentures embedded with reinforcing materials. This is because the light beams cannot pass through the reinforcement. The finite element method (FEM) has been used for numerical stress analysis. The method is superior to experimental methods because it can perform the stress analysis of complex geometries, such as dentures embedded with reinforcement material, and evaluation of the stress results in detail. Additionally, analytical methods for stress analysis of dental implants have been developed [25,26]. However, it is quite difficult to apply analytical methods to complex implant structures such as maxillary dentures with reinforcing materials. Therefore, there is much research showing that the finite element method is the most effective method for stress analysis of denture base materials [2,8,11,27]. However, the effect of temperature changes on stresses in dentures was not considered in those studies. Although the placement of reinforcement materials inside PMMA dentures reduces stress at critical points of maxillary dentures, the risk of damage due to thermal expansion may increase with the change in temperature. Thermal expansion coefficients of PMMA and fiber reinforcements used in maxillary dentures are different from each other. This difference may cause serious distortion and increase stress in critical areas when cold or hot food is consumed. Normally, the standard temperature in the mouth changes from 32 \({}^{\circ}\)C to 37 \({}^{\circ}\)C, but when patients consume hot/cold drinks or food, the oral cavity temperature increases by a range of 0 \({}^{\circ}\)C to 70 \({}^{\circ}\)C [28]. The effects of temperature changes on stress at critical points in maxillary dentures with reinforcement material have not been extensively studied in the literature. In our study, the finite element method was used to evaluate thermal stress analysis of maxillary dentures with reinforcement material.