## 4 Discussion  
The present retrospective longitudinal study aimed to evaluate the outcome of implant-supported restorations after 5 years of function. Regarding the present study outcomes, the marginal bone level stability measurements could be addressed to the implant to abutment stability. This is directly influenced by the type of connection, even if platform switching may help achieve ridge dimension preservation and enhance the stability of peri-implant soft tissues [26]. In fact, the role of platform switching on the stability of the peri-implant hard tissue is still unclear [24; 25; 27; 28], and controversy  
Figure 4: The 5 year marginal bone loss changes from the implant loading are shown in Figure 4. Every line is an implant, and the red line is the mean value of marginal bone loss. Figure 3: Cumulative frequency distribution of average bone loss at patient level (every square is a patient. The x axis is a mm scale and in the y axis we have the cumulative frequencies). on hard tissue preservation with the platform switching technique remains unsolved [29]. Nevertheless, bone-level implants have been created with many connection configurations. Locking-taper conical connection implants have proven superior to buttress joint implants at achieving a tight seal and eliminating the micro-gap at the implant-to-abutment junction and have demonstrated improvements in crestal bone maintenance. According to these findings, the internal-conical-connection of the implants included in the present report seemed to positively influence the peri-implant bone stability [19; 20; 21; 22]. Several potential risk factors that might influence peri-implant tissues and implant failures were also evaluated. Other studies by [PERSON] et al. [26] reported a similar 5 year failure rate, specifically a failure rate of 5.3% at the PFD (partial fixed dentures) level and 2.7% at implant level were calculated and a good medium-term prognosis of implant-supported rehabilitations was confirmed. Only a smoking habit, even related to smokers that smoke up to 10 cigarettes per day, was found to be statistically significant as far as bone loss is concerned. Indeed, 0.5 \(\pm\) 0.5 mm of bone loss was suffered by implants placed in smoker patients while non-smoker patients experienced an average marginal bone loss of 0.3 \(\pm\) 0.3 mm. It could be assumed that patients reporting to be light smokers stated facts that were not entirely true. Similarly, a systematic review conducted by [PERSON] et al. in 2016 [30] agreed with such outcomes, reporting a statistically significant difference of marginal bone loss when considering smokers versus non-smokers. To be more precise, a range of bone loss between 0.07 and 0.9 mm with a mean value of 0.5 mm was reported. Nevertheless, the clinical significance of 0.2 mm of bone loss might be questioned. Since smoking was the only statistically significant risk factor, no multilevel analysis was performed to compare other variables. In the end, average bone loss around implants might not be affected by factors such as sex, insertion site and prosthesis type. In this respect, the same parameters were evaluated in a prospective study accounting for 630 patients and 1569 implants, which was conducted by [PERSON] et al. [31] in 2017. The authors reported that incidence of implant-related complications was not significantly influenced by implant location, age, sex, or implant placement associated with GBR procedures. In the present study, Figure 3 on 5 year bone loss changes could be superimposed to the outcomes of [PERSON] and [PERSON] [16]. In such a scenario, the authors analyzed the bone loss pattern of peri-implantitis-associated bone loss on 419 implants with up to 23 years of observation. To summarize, a tendency of 0.15 mm peri-implant bone loss per year was predicted by the authors. In the present analysis, a similar trend is displayed.