## 4 Discussion
Moreover, with the use of metallic sleeves, the risk of overheating the bone during drilling increases due to inadequate saline irrigation [15]. [PERSON] et al. proposed a new design of a surgical guide for avoiding increasing temperature during the drilling process and allowing the irrigation flow to reach the drill during osteotomy [42]. A FEA was carried out with the aim of anticipating the temperature in the bone while drilling but applying PMMA properties instead of bone characteristics. The authors claimed that for the new guide design, the circulation of irrigation is better in comparison to the conventional design [42]. However, the surgical guide analyzed in our study has a built-in window to allow cooling during the drilling process. This type of guide design has been successfully used in many clinical cases. without the risk of bone necrosis due to overheating during osteotomy bed preparation when the recommended protocol was followed [3; 4; 5; 8]. Despite the fact that the areas with maximum stresses appear at the built-in window, the von Mises stress did not exceed 6.92 MPa, far below the risk of resin guide brakee (failure). However, when the guide design needs to be modified, in some clinical cases due to a lesser meso-distal space, the custom reduction of the guiding cylinder needs to be performed with caution due to the risk of exceeding stress during drilling and, consequently, surgical guide brakee. Recent research [42; 44; 45; 46] confirms the importance of studying the behavior of the guide through simulation and real tests and brings valuable results regarding the values of the forces and moments that load the guide and the mandible bone in the drilling process. Most authors propose certain values for these loads depending on some conditions, obtain results, and draw conclusions that surgeons should take into account in their practical work in dental clinics. For the FEA analysis, the data are typically recorded in.stl files, a format original to 3D printing technology in which only the 3D surface geometry is described in a triangular mesh. Generally, the.stl mesh guides the construction of the geometric model, but not the FEA mesh, since it does not have sufficient data and consistency, complexity is too high, and/or is characterized by triangles with compromised edges, missing faces, or an incorrect orientation, self-intersecting mesh elements, e.g., It is well known that a finer mesh results in a more accurate solution. However, using the finest mesh in the whole model is usually a bad strategy because unnecessary calculations will be performed, producing a useless computational cost. The mesh convergence study enables the acquisition of a mesh that satisfactorily balances accuracy and rationalization of computing resources [47]. Thus, the 3D model of the guide must be verified, simplified, and optimized, as we did in our study, to be easily transferred to the complex stages of finite element analysis. The guide was designed as.stl file with a great number of triangles (82,180). With such a large number of triangles, the analysis with finite elements could not have been carried out on our computers; the complexity of the model would have been too high and unnecessary, it would probably have introduced geometry errors in the later stages of the analysis. After the simplification stage (reduction to 2818 triangles with the Simplification tool), no significant differences in area or volume are observed in the guide model. Simplifying complex models is a common and recommended practice. Of course, if, during the analysis, some limit values appear that can influence the results and conclusions, the user should run a new simplification using another accuracy factor. In the application presented in the paper, the accuracy factor has a value of 0.5 (as can be seen in the video at minute 8.06 [26]). The 3D model was discretized using a minimum mesh size of 0.5 mm with an absolute sag of 0.2 mm.