## 4 Discussion  
While exact proof showing that high mechanical stress levels evoked during implant insertion inevitably cause bone resorption is still missing in the literature, growing evidence seems to indicate that less trauma during implant surgery reduces initial bone loss [2; 5; 9; 10]. In this context, this FEA study aimed at comparing two different implant macrodesigns  
Figure 11: Reaction moments of the implant SCI (**a**) and the implant MT (**b**). While for SCI, a continuous increase is clearly visible during the insertion process, reaching up to 300 Nmm, MT shows maximum values around 80 Nmm when the bulky portion of the implant passes the cortical layer of bone. with respect to stress and strain generation in bone during the insertion process as well as the amount of bone cut and transported along the osteotomy walls. As expected, the novel implant caused maximum stress and strain when the middle part with increased core diameter and blunt threads passed the cortical layer of bone. Less stress and deformation were observed during the final stages of implant insertion when the deeper and sharper threads engaged the cortical layer of bone. The conventional, tapered implant caused less stress during the initial phase of insertion, until reaching its cervical third, which then led to much greater stress as observed with the novel implant. This maximum stress state remained at its level upon seating the implant. This behavior is in accordance with previously conducted strain gauge studies using polyurethane foam as a bone surrogate material [17]. While not evaluated in this simulation, the engagement of cortical bone at low stress levels seen with the MT implant compared to implant designs featuring a cervical back taper [20] or triangular/tri-oval cross-section [14; 15] seems advantageous in areas with limited bone quantity and bone quality. As per manufacturer recommendation, a 3.5 mm osteotomy was simulated for both implant types despite the conventional, tapered SCI implant having a 0.1 mm smaller diameter compared to the MT implant. This has to be considered as an additional variable when interpreting the findings presented, as even more favorable values could have been expected if the amount of undersizing had been equal for both implant types. An alternative would have been to harmonize the amount of undersizing of the osteotomy relative to the implant diameter. As evidenced by the amount of bone cut and transported along the walls of the osteotomy, the MT implant engages bone almost over its whole length, while the conventional implant mainly engages bone in the cervical part. As such, this study appears to demonstrate that the novel implant derives primary stability through compression of trabecular bone instead of cortical bone [18; 19] as observed in the conventional conical implant and recently described in an in vitro study [31]. This finding is also in line with two previous experiments conducted on bone surrogate materials using the MT implant [17; 20]. As with every finite element analysis, specific limitations have to be considered, limiting the clinical validity of the data presented. Despite using a CBCT-derived bone model as well as exact implant geometries, this study only allows for relative comparisons between the two specific implants tested. Attempting to closely simulate clinical reality, assumptions had to be made with respect to cortical bone thickness, insertion velocity, and friction between implant and bone. Furthermore, bone was simulated as an ideal composite consisting of two distinct compartments, and the material properties of bone were modeled as being isotropic, elastic-plastic. This clearly constitutes a methodological limitation, as real bone at the continuum scale would show anisotropy and heterogeneous composition. To overcome these limitations, the material model could be improved by using bone density-related stiffness and including elastic transversal anisotropy.