## 1 Introduction  
Implant treatment has shown high long-term survival rates [1; 2; 3; 4; 5; 6] and is considered an acceptable choice to replace missing elements. Nevertheless, implant-related mechanical or biological complications have been extensively reported and, in order to assess peri-implant status and to verify implant success rates over time [7; 8], radiographic detection of marginal bone loss (MBL) is considered a primary diagnostic device [9]. Several factors may influence MBL levels, such as surgical trauma, occlusal overload, implant positioning, plaque accumulation and biologic width reformation [10]; furthermore, the implant-abutment interface (IAI) design could also play a key role. A bone loss of 1.5 mm to 2 mm below the IAI in the first year of loading has been reported [11; 12] for dental implants restored using a platform matching (PM) abutment with a supracetal positioning and/or transmucosal healing [8; 13]. [PERSON] and [PERSON], therefore, have proposed and introduced the platform switching (PS) concept [11], which allows iso- and subrestal implant positioning and aims to reduce the amount of marginal bone loss [11; 14]. After explaining the negative effect of the implant-abutment microgap, which is strongly correlated with bacterial leakage and the formation of a chronic infiltrate [15; 16], several authors demonstrated that by placing narrower prosthetic abutments on larger-diameter implant platforms, the IAI is displaced inward from the implant shoulder and ahead from the bone level [14; 17]. Hence, the inflammatory connective tissue infiltrate is principally enclosed beyond the implant platform, protecting the crestal bone. This procedure, along with the ability of PS implants to distribute loads and concentrate forces, reduces peri-implant bone resorption, increasing, therefore, the long-term results of dental implants [14; 18; 19]. Furthermore, [PERSON] et al. [20] performed a histological evaluation of an implant removed 2 months after placement and hypothesized that the inward shift of the inflammatory connective tissue zone at the IAI could lead to lower bone resorption around PS implants [20], reinforcing, therefore, the [PERSON] and Porter study [11]. Moreover, [PERSON] et al. [21] did not find out any statistically difference in MBL levels between PS and non-PS implants. Apart from the use of PS abutments, the design of the implant neck might also influence the esthetic and functional outcome of prosthetic rehabilitations, and there is currently a lack of knowledge on the long-term results on the comparison between PS and PM dental implants, although few studies reported positive outcomes [22]. The adoption of a prosthetic workflow able to avoid continuous dis-reconnection was demonstrated to additionally reduce MBL changes in case of PS restorations, minimizing the connective tissue microdamages [23]. On the contrary, the literature on the influence of the implant neck (bone level vs. tissue level) on MBL is still controversial: several systematic reviews with meta-analysis [24; 25; 26; 27; 28] reported contradictory results. According to [PERSON] et al. [24], there were no statistically significant differences in MBL levels between bone-level (BL) and tissue-level (TL) implants. Similarly, [PERSON] et al. [27] reported no difference in MBL between submerged and transmucosal implants. However, articles included presented a more limited follow-up of only 12 months. Moreover, [PERSON] et al. [26] concluded that there was not sufficient evidence to evaluate the superiority of BL implants. Despite this, the authors suggested that the considerable heterogeneity of the studies included may have influenced the results of their meta-analysis. On the other hand, [PERSON] et al. [28] concluded that BL implants showed significantly less MBL after 1 year of loading than TL implants. Implant placement in the esthetic zone is extremely challenging for clinicians, and patients' expectations for long-term, stable results might be quite demanding [29].