## 4 Discussion
Our results show the mean ISQ value at the time of surgery in the posterior area 60.4 \(\pm\) 0.4 for smokers and 62.9 \(\pm\) 0.6 for non-smokers and at the time of loading 64.0 \(\pm\) 0.5 and \(67.2\pm 0.6\), respectively. It could be noticed that at the time of surgery in posterior region of maxilla the majority of smokers cases are on the verge of eligibility for immediate implantation, while non-smokers exceed these requirements and can be easily recommended for two-stage conventional loading implantation. After six months the loading of smokers' implantsshould be performed in caution (may be with the use of temporary not fully loaded crown for a few months), while non-smokers implants may be loaded with permanent crown. Our results show the mean ISQ Value at the time of surgery in the aesthetic area \(58.5\pm 0.4\) for smokers and \(60.0\pm 5.1\) for non-smokers and at the time of loading \(65.52\pm 5.05\) and \(67.61\pm 5.11\), respectively. It could be noticed that at the time of surgery in aesthetic region of maxilla the majority of smoker cases are below of eligibility for immediate implantation, while non-smokers, in most cases, meet these requirements. After six months the loading of smokers' implants should be always performed in caution (with the use of temporary not fully loaded crown for a few months), while non-smokers seems to be ready for permanent loading. Results from previous studies involving implant stability, measured by resonance frequency analysis, are heterogenous. Most of the authors conclude that tobacco consumption is not associated with differences in implant stability [8, 11, 12]. A recent study by [PERSON] et al. reported that primary implant stability was not affected by smoking, while secondary stability may be lower among smokers. Moreover, during the healing period, implant stability among smokers decreased by 0.91 ISQ points, while in non-smokers it was increased by 2.69 ISQ points, during osseointegration [13]. On the other hand, [PERSON] et al. showed that stability of implants in smokers was significantly higher than in non-smokers on the day of implantation, and 1 day, 7 days, and 14 days after surgery. However, at 28 days post-implantation the difference between these two groups of patients was not significant [14]. Diverse research protocols and surgical procedures hinder direct comparison of results obtained. Available results regarding the effects of smoking on implant stability are significantly variable which indicates the need for further exploration of the osseointegration process and clarification of the factors contributing to the discrepancies observed. A recent meta-analysis by [PERSON] et al. indicates that smoking cigarettes increases the marginal bone loss around implants by 0.11 mm per year on average [1]. Other meta-analyses confirm increased marginal bone loss around implants in smokers [33, 34]. In the current study the marginal bone loss after 18 months was lower than most of the reported results included in the above-mentioned meta-analyses. This may be attributed to different surgical techniques. In our study, the marginal atrophy observed in the alveolar bone was not significantly different between smokers and non-smokers, both in the aesthetic as well as posterior regions of the maxilla, 18 months after prosthetic loading. The differences in implant stability between smokers and non-smokers in the current study were similar at all time points. Statistical analysis of the implant stability growth dynamics based on the ISQ value increase did not reveal significant differences between the two groups (aesthetic area \(p=0.124\), posterior area \(p=0.188\)). It can be concluded that smoking did not noticeably affect the osseointegration process itself, during the 6-month post-implantation period. A study by [PERSON] et al., comparing the process of osseointegration between heavy smokers and non-smokers showed that the healing process after implantation may be slower in smokers.