## 6 Cooling Methods and Their Effects on PMMA Bone Cement Properties  
There have been several attempts made to reduce the maximum temperature values reached during the course of the polymerization reaction of PMMA [25; 43; 44]. The first method was the so-called \"on-off technique\", involving intermittently removing and replacing the putty index during polymerization. This has been shown to have a significant effect on reducing the intrapulpal temperature, meaning that the maximum temperature rise is only 1.94 \({}^{\circ}\)C compared to the 11.04 \({}^{\circ}\)C of the control group. This technique, however, has limited use in the context of orthopedics [43]. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Method** & & **Effect on Polymer Conversion** & **Key Considerations** \\ \hline Pre-cooling of Cement/Components & - & May slow polymerization, reducing peak temperature but potentially delaying full conversion & - & Requires optimization to balance thermal safety and conversion rate \\ \hline Use of Phase-Change Materials (PCMs) & - & Absorts heat during polymerization, lowering temperature peaks & - & Studies suggest a minimal impact on conversion when PCM concentration is optimized \\ \hline Alternative Monomers (e.g., Glycidyl Methacrylate) & - & Alters polymerization dynamics, typically maintaining high conversion & - & Mechanical properties remain intact, though further testing is needed for long-term outcomes \\ \hline Nanoparticle Additives & - & Can promote even heat distribution, potentially supporting uniform polymer conversion & - & Specific nanoparticle types (e.g., magnesium oxide) can enhance polymerization without compromising properties \\ \hline Vacuum Mixing & - & Reduces air entrapment and peak temperature while promoting consistent conversion & - & Shown to reduce porosity but requires controlled application \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The effects of cooling methods on the rate of polymer conversion. Another avenue of research was the application of dentin bonding. This provides a thermal barrier, reducing the temperature increase to 9.53 \({}^{\circ}\)C, with this being slightly more ineffective than the on/off method [25]. Cooling the cement of the metallic components of the prosthesis has been shown to have an effect in mitigating the temperature of the polymerization reaction, however, it also extends the handling time significantly. This has its uses in the field of verteboplasty, allowing surgeons to extend the time in which they fill the defects with cement as a bone substitute [22]. Ice baths can also extend the fluidity of bone cement, allowing a more controlled treatment on multiple levels [44]. Keeping the initial cement and metallic components at room temperature prior to mixing has also been shown to minimize the temperature peak and thus reduce the risk of thermal necrosis occurring [45]. Researchers have observed that cooling the PMMA bone cement through various means in order to combat the high temperatures of an exothermic polymerization reaction has a significant effect on the mechanical properties. This generated heat can affect both the mechanical integrity of the cement and the longevity of the implant. Peak temperature values and the length of exposure are both critical factors when calculating the extent of thermal necrosis. Bone tissue can withstand a temperature of up to 56 \({}^{\circ}\)C, this being the threshold commonly agreed upon to be dangerous when it comes to thermal necrosis, and studies have shown different types of PMMA bone cement can exceed this value during peak temperatures [46]. Several attempts have been made in pre-cooling the prosthesis or the femoral canal before implantation. This can be effective when trying to lower the peak temperature of the polymerization reaction. Studies conducted by [PERSON] et al., [PERSON] et al., and [PERSON] et al.