## 4 Discussion  
The results of the current study indicate that smoking tobacco has a negative impact on implant stability following immediate implantation in the aesthetic, as well as posterior regions of the maxilla. The marginal bone loss around implants was not significantly different between groups 18 months after prosthetic loading. Dental implant stability is the key factor enabling proper healing, and, therefore, the success of the implantoprosthetic treatment and depends on the bone quality, implant properties, as well as surgical technique [27; 28]. The thread pitch, in implants we used, is 2.4 mm what seems to be a lot, but it is compensated by the double thread design which results in maximum 1.2 mm distance between single threads. The implant primary stability is also enriched due to variable thread design wider in the coronal part and deeper in apical direction. In results this may provide high primary implant stability, even in soft bone. Periodest measurements in the aesthetic area showed no significant differences in implant stability on the day of implantation, and 24 months after surgery between smokers and non-smokers. Although at the time of prosthetic loading (6 months after surgery), smokers displayed lower implant stability than non-smokers. In the posterior area of the maxilla implant stability was lower in smokers on the day of implantation, as well as 6 months after. [PERSON] et al. found no significant differences in PT values in general when comparing smokers to non-smokers, however they revealed that higher Periotest values (lower stability) were correlated with increased risk of implant failure. Moreover, the success rate of the treatment was significantly lower in smokers when compared to non-smokers (84.2% and 98.6%, respectively). Increased tobacco consumption resulted in more pronounced differences, as the failure rate after 5 years rose to 30.76% among patients who smoked more than 20 cigarettes a day [10]. [PERSON] et al. similarly found no differences in Periotest values between smokers and non-smokers [9]. After 2 years of follow-up no implant failure was observed in both groups of patients. The differences observed in the above-mentioned studies, which described implantations performed in a healed alveolar crest, may be attributed to the different type of surgical protocol, since our patients underwent immediate implantations involving intra-alveolar augmentation with a xenogenic bone substitute. It has been build up evidence that excessive mobility of implants, exceeding the threshold of about 150 microns, inhibits the osseointegration process and may lead to the formation of a connective tissue layer between the implant and the surrounding bone [29]. Moreover, available clinical stability measurement methods, such as resonance frequency analysis used in Oostell device, have been described as suitable to predict the risk of implant failure, based on secondary stability measurements [30; 31]. It is of a great importance that RFA and Insertion Torque Value represent two different features of primary stability. The RFA indicating the resistance to bending load, the ITV indicating the resistance to shear forces [21]. The measurement of ITV or RFA may be significantly overstated in the case of a thick cortical bone, that provides primary stabilization of the implant only in its narrow section in contact with the cortical bone, while the implant may not achieve stabilization in the part emerged in the cancellous bone. In these cases, dynamic measurement methods such as VTW (Variable Torque Work) or IE (Insertion Energy) are essential to establish the actual force, the implant is stabilized in the bone. In our study all the cases were immediate implantation to the fresh alveolar sockets, that mean the cortical bone was missing. The bone was III or even IV class by Lekholm and Zarb classification [19]. This is why RFA seems to be reliable method of primary implant stability assessment and correlated with VTW and IE in these bone conditions [32].