## 4 Discussion  
The values for implant stability can be affected by many factors, though not in the same proportions. [PERSON] and [PERSON] investigated the influence of bone density structure and implant length on stability levels, and reported that the length of the implant influences the implant stability only at the time of the surgery and has lesser impact on further stages of osteointegration. Conversely, bone density seems to influence the stability level in a greater way and on all stages of osteointegration [17]. Subsequently, to standardize the sample population, we selected homogenous bone sites of the frontal aspect of the maxilla as a region of interest. In our study, a decrease in the stability level in the four weeks following the implant insertion was observed (Figure 4). These results are in accordance with other studies and suggest the existence of bone resorption in direct contact with the implant surface. This behavior is attributed to the time dependency of bone remodeling observed at the initial stage. Therefore, the bone shape and remodeling toward the implant surfaces interfere with the bone-implant contact [18; 19]. [PERSON], in the study on 4.0 and 4.1 mm diameter implants, reported the decline in implant stability at 21 days after surgery for the hydrophilic SLActive implants to 78.8 \(\pm\) 2.6 ISQ, and to 78.4 \(\pm\) 3.2 ISQ at 28 days for hydroxyapatite coated implants. However, hydroxyapatite coated implants regain the secondary stability much faster (42 days) when compared to SLActive implants (68 days) [19]. Regarding the primary stability levels, there is a consensus that ISQ values above 70 are optimal for osteointegration to occur, and they enable the consideration of immediate implant loading. In contrast, the ISQ value of 55 for primary stability is the threshold value for the possibility of leaving the implant in place. Below this value, the implant should be replaced with an implant that enables higher primary stability [18; 19; 20; 21]. However, there are studies reporting that modification of the implant's surface in nano-scale allows for successful early loading even in the case of a lower than optimal primary stability level. [PERSON] et al. compared 242 oxidized surface implants, loaded immediately and delayed. Apart from the relatively low primary stability levels (62.9 \(\pm\) 4.9 ISQ) of immediately loaded implants, the overall success rate was high (99.2%) in that group. Furthermore, the MBL level for immediately loaded implants during 12 months of observation was 0.78 \(\pm\) 0.9 mm and seems also acceptable [22]. Subsequent studies addressing this subject demonstrated a correlation between low baseline values of RFA and the potential for implant loss due to lack of osteointegration. [PERSON] assessed the primary stability value of 17 implants that were lost within the first year of use. It was found that the average ISQ value in that group was 54.6, whereas the implant group with successful treatments had an average ISQ value of 62.0 [23]. Other studies reported an average primary stability value of 63.3 ISQ in the group of implants that survived the 12-month follow-up period, whereas, in the group with lost implants, the average primary stability value was 56 ISQ [24]. Some studies have found a slightly lower (56 ISQ) threshold value for primary stability, which is necessary for osteointegration to occur [25; 26]. That is why it seems that, apart from the established consensus, this issue is still a current topic and further studies are needed for its full development. [PERSON] et al. included the implant diameter in the assessment of the levels of secondary stability. The ISQ value measured three months after the insertion of implants with a diameter of 3.7 mm was 69.62, while for implants with larger diameters (4.0 mm and 4.3 mm), that value was 72.02 and 69.67, respectively [27]. This finding is in agreement with the following study results (Figures 4 and 5). In the following study, hydrophilic surface implants were applied.