## 8 Factors Influencing Temperature and Mechanical Properties of PMMA Bone Cement
These methods mutually contribute to better fixation and durability of the implant through regulated polymerization heat [24]. Thermal necrosis represents a challenge in orthopedic and craniofacial procedures, where elevated temperatures endanger the viability of adjacent osteocytes, thereby facilitating the onset of osteeocrosis. This thermal damage to bone tissue impairs cellular integrity and function, leading to irreversible bone death and compromised healing. In hip replacement surgery, a thicker cement mantle poses a risk for early mobilization of the implant, and in craniofacial surgery, a mantle thicker than 6 mm leads to an uncontrolled temperature increase and may result in significant bone and dural necrosis [23]. Another characteristic of bone cement affected by thickness is the setting time and viscosity, impacting the ease of application and potentially leading to a suboptimal fixation of the implant. Mechanical strength may also be compromised, and despite a thicker mantle offering a stronger fixation, the increased temperature that results from the thicker mantle weakens the surrounding bone tissue by decreasing its viability and poses a risk for early mobilization [24]. In the study by [PERSON] et al., loading bone cement with minerals such as sodium borate (borax) and calcium borate (nobleite) enhanced the structural integrity and antibacterial properties of the cement while mitigating risks from exothermic reactions. Specifically, sodium borate-loaded cement, when tested under 0.100 MPa pressure, showed deformation percentages between 12.58% and 10.67%, depending on the loading concentration. Calcium borate-loaded cements showed deformations from 12.54% to 9.87%, reflecting both improved mechanical stability and effective heat distribution across varying mineral concentrations [23; 34]. Different mold materials and geometries have been shown to affect the thermal properties of PMMA bone cement during polymerization. These factions can also influence the mechanical properties of the cement. Poor heat-conducting materials like polyurethanefoam minimize the peak temperature values significantly, though this has no use in the context of orthopedics from our current understanding [62]. The polymerization reaction is highly exothermic, it generates a significant amount of heat that has an effect on the porosity within the cement. The heat also leads to thermal necrosis and, if not managed, further endangers the stability of the implant [22; 71]. Porosity in PMMA bone cement can arise from several different sources, including polymerization shrinkage and due to the exothermic reaction itself. Shrinkage stresses in bone cement were theoretically analyzed by [PERSON] et al. using thick-walled cylinder theory to estimate the interference stresses associated with thermal and total shrinkage. In this model, thermal shrinkage was determined using the coefficient of linear thermal expansion for bone cement, while total shrinkage was directly measured. The modulus of elasticity for acrylic bone cement was found to range between 2.1 and 2.7 GPa, with [PERSON]'s ratio values varying from 0.38 to 0.46, both of which were experimentally determined and used in the stress calculations. Focusing on the thermal component, the model predicted circumferential stresses in the cement mantle, ranging from 8.4 to 25.2 MPa at curing temperatures between 60 and 140 \({}^{\circ}\)C. This finding indicates that temperature increases during cement curing significantly contribute to circumferential stresses, underscoring the impact of thermal shrinkage on stress development in the cement mantle. These stresses are likely to influence the mechanical integrity and longevity of cemented implants, particularly under cyclic loading conditions, suggesting that further experimental validation and refinement of the model may enhance our understanding of stress distribution in clinical applications [23; 72]. Changing the composition of bone cement or utilizing additives to lower the peak temperature values also influences porosity.