## 4 Discussion
Therefore, maintenance of pulp health and dentin safety is a fundamental challenge; in addition, it is important to determine the critical temperature at which damage may occur. [PERSON] and [PERSON] stated that if the temperature changes within the pulpal chamber exceed the critical limit of 5.5 \({}^{\circ}\)C, these changes will result in pulp necrosis. This critical threshold has been considered in many reports and studies [38]. Overall, the results of the temperature distribution at the outer surface were different from those obtained inside tooth structures in both vertical and horizontal directions. In accordance with our simulation results, thermal changes promoted by cold loading simulations were identified to be more effective than those induced by hot loading simulations. This is mainly due to the transfer of heatby convection to the outer surface, in which cold thermal loading shows a larger heat convection coefficient value and temperature difference than hot loading, which is in good agreement with the literature [19; 39]. The highest pulp temperature was seen in the conventional design, which was considered to be near the critical temperature for pulp injury, while in dentin, the temperature change for cold loading was below the physiological limit. This thermal change may induce tooth thermal sensitivity as a result of dental fluid flow (DFF) in the dentine tubules that can transmit a considerable amount of heat to the pulp chamber causing sensitivity; in addition, the pulpal blood flow (PBF) rate decreases during cooling [40]. While the thermal temperature changes in both the non-preparation and proposed preparation designs were within the physiologic limits and were not strong enough to harm the pulpal nerves or promote dentin sensitivity compared to the conventional design, these differences were due to less removal of dentin and enamel during preparation, in addition to the poor thermal conduction properties of the dentin microstructure, which is in good agreement with the outcomes observed previously [40; 41]. Thermal variations in the oral environment are ultimately responsible for stresses that have an important effect on the lifespan of restorations by inducing microleakages, chipping, cracks, and fractures. Based on our results, all the models exhibited the maximum von Mises stress values in each studied layer under the cold thermal loading, and these values were higher than those under the hot thermal loading. In the assessments of the thermal stresses, the largest stress was concentrated on the veneer surface, which is the area in contact with the thermal load. Among the tested models, the proposed preparation design showed relatively lower von Mises thermal stress values than the conventional and non-preparation designs, which were more durable under these thermal conditions. Additionally, stress distribution in the incisal areas is higher than that in the cervical areas, which may promote chipping and fracture in the veneer; furthermore, stresses on palatinal surfaces were higher than those on the buccal surfaces. This action is based on the high elastic modulus and the coefficient of thermal expansion properties of ceramic veneer, which therefore exhibited higher thermal stresses. The accumulation of thermal stresses in the bonding layer may lead to inner flaws in the cement layer, which cause crack propagation and microleakage. Furthermore, polymerization shrinkage, function, and thermocycling contribute to premature debonding, and the intrinsic tensile stress contributes to the damage to the ceramic veneer. These findings were in agreement with those of previous studies [19; 30]. As FEA is a numerical tool, some aspects of the oral environment, such as the non-linear elastic characteristics of the PDL tissues and the anisotropic feature of dentin were not considered since they require substantial experimental data.