## 4 Discussion  
The aim of this study was to evaluate whether autoclaving changes the Vickers hardness and flexural modulus of resin materials used to additively manufacture insertion guides, which could pose a risk for the accuracy of static navigated implantation. For the majority of specimens, the two autoclaving protocols had a minor impact on the flexural modulus, whereas changes in the Vickers hardness were more pronounced. Looking at the results of the Vickers hardness testing, it seems that choosing the right autoclaving cycle might decrease the risk of hardness deterioration of the templates. In one out of the three groups exhibiting significant autoclaving-induced changes in the Vickers hardness (group 2), these changes occurred after the cycle 2 sterilization protocol (134 \({}^{\circ}\)C, 2 bar for 5.5 min) and not with the so-called \"delicate\" program cycle 1 (121 \({}^{\circ}\)C, 1 bar for 20.5 min). Overall, none of the materials that are authorized for autoclaving by the manufacturers showed signs of decreasing Vickers hardness after being autoclaved with cycle 1. Still, it is questionable whether the increase in hardness could be accompanied by a contraction of the material, which could lead to dimensional changes of the templates. Our results showed that in most cases, autoclaving does not significantly change the flexural modulus of resin materials used to print the templates. Thus, it seems that autoclaving might not be a major risk factor for implantation accuracy loss caused by significant changes in the flexural modulus. We found no significant changes in the flexural modulus for groups 2, 3, and 4. Interestingly, a decrease in flexural modulus was also seen in group 0, which was expected to be more prone to heat-induced changes in the flexural properties, as that resin is not authorized for autoclaving. Nevertheless, for most of the groups, the flexural moduli decreased to some extent. In group 1, autoclaving significantly decreased the flexural modulus, independently from the cycle. Avoiding medical risks related to the contamination of the surgical site is the primary reason that makes autoclaving a must. It has been shown that the immersion in different disinfection solutions such as chlorwechidine digluconate, sodium hypochlorite, sodium perborate, or glutaraldehyde cannot entirely eradicate the microbial contamination of surgical template surfaces made of acrylic resin [31,32]. Ethanol at 70-80% resulted to be most effective among the disinfectants [25,32]. [PERSON] et al. found that, after immersion disinfection with 70% ethanol for 15 min, about 16% of colony-forming units (CFU) remained on the resin surfaces [25]. Hence, in accordance with the risk mitigation when utilizing medical devices, as requested by the EU Medical Device Regulation [6], the sole reduction in microorganisms on surgical template surfaces by immersion disinfection seems insufficient and sterilization should be chosen. In light of our findings, the biological benefit of autoclaving the templates outweighs the risk of changes in the flexural properties or Vickers hardness. Nevertheless, some authors suggest cold sterilization protocols for heat-sensitive resin materials, i.e., utilizing ethylene oxide gas [33], which, however, are not commonly utilized in dental practice. The investigation of high-temperature sterilizing protocols such as autoclaving is clinically relevant, as it is one of the most commonly used methods in dentistry [34, 35, 36, 37]. In agreement with our results for groups 1, 2, and 4, a pilot study by [PERSON] et al. found that additively manufactured template materials did not significantly change in hardness when subjected to 121 \({}^{\circ}\)C autoclaving [27]. Our observations differ to some extent, as we found significant changes of the hardness for group 3 after 121 \({}^{\circ}\)C autoclaving. Furthermore, their investigation on specimens that had been autoclaved at 134 \({}^{\circ}\)C exhibited significant changes in hardness values compared to specimens that were left untreated.