## 4 Discussion  
As it has been already reported in the literature, the insertion of an implant platform in a more apical position relative to the alveolar crest could give better aesthetic results [13; 14]. However, only implants that presented a very low percentage of bacteria at the IAJ level could be safely inserted in a subcrestal position [43; 44; 45; 46; 47; 48]. Different experimental, clinical, and radiological results have been reported when Cone-Morse implants were inserted in a subcrestal position; however, a consensus on this topic has been never reached [18; 20; 25; 27; 28; 32]. In animal experiments and in human histological studies on retrieved Cone-Morse implants, it was found that no resorption or a smaller amount of resorption of the peri-implant bone was present, and also that, in some specimens, newly formed bone tended to overgrow the implant shoulder and the micro-gap, touching the abutment surface [13; 14; 21; 30; 43; 44; 45; 46]. Overall, a systematic review with meta-analysis reported that in most of the evaluated papers no differences were found in peri-crestal bone levels of equicrestally and subcrestally situated implants [24]. In addition, clinical reports corroborated these data with similar results [22; 23]. Other FEA studies have also found a significantly greater strain peak in external hexagon connections when compared to Cone-Morse connections [39; 40]. Moreover, it was also reported that peak stresses were moved away from the crestal peri-implant bone to subcrestally positioned implants [7; 16]. The cortical bone is responsible for transmitting occlusal loads to the implant bone interface, due to its high stiffness compared to the trabecular bone. For this reason, implants inserted in a subcrestal position that do not have contact with the cortical bone exhibit distinct mechanical characteristics compared to those placed in a more crestal position. It has been observed that the maximum compression stress value on the bone provides useful information to analyze bone resorption with respect to the tension stress value [10]. In particular, [PERSON] et al. [19] provided evidence of bone resorption resulting from stress overload when compression stress exceeds the range of 80-130 MPa on the cortical bone. In contrast, the present study found that an equicrestal implant positioning, coupled with the application of an oblique load, resulted in a stress level of 60 MPa on the cortical bone. However, when using subcrestal placements, significantly lower and safer stress values of 20 and 15 MPa were observed. Consequently, this reduction in stress can be attributed to the placement of the implant at a depth of approximately 1.5 mm, leading to the growth of coronal bone at the interface and contributing to an increased success rate. In the present FEA study, it was observed that as the depth of implant placement increased, there was a corresponding rise in compressive stress on the apical region of the implant, as shown in Figure 7. This occurrence can be attributed to the displacement of the fulcrum of force towards the apical region, resulting in a greater lever arm. This displacement is caused by the increased interaction between the implant and trabecular bone, leading to the observed phenomenon. In addition, the reduced section of the apical area of the implant decreased the contact area available to dissipate stress with the bone, and therefore, there is an increase in stress. These observations provide a potential explanation for the  
Figure 7: Comparisons of stresses detected within the bone around equicrestally and 1 mm and 2 mm subcrestally placed implants. critical significance of the system design, particularly in the apical area, when choosing the subcrestal implant positioning. To ensure appropriate implant placement, it is crucial to carefully assess occlusal loads. Therefore, conducting these evaluations prior to any occlusal adjustments is imperative in order to mitigate the risk of bone resorption resulting from elevated stress levels.