## 1 Introduction  
Immediate post-extraction implants are a widely debated topic in the literature. In previous studies, this method was recommended by some authors [1; 2; 3; 4; 5]. The reason for this type of decision regarding immediate post-extraction implants essentially lay in the fact that it was believed that the bone remodeling carried out subsequently could be reduced, in order to avoid the occurrence of mucositis and, subsequently, peri-implantitis uncovering the implant threads. However, uncertainty regarding bone remodeling in the case of an immediate post-extraction implant is particularly significant in cases in which an immediate post-extraction implant is inserted in the upper anterior areas. In such cases, potential bone resorption can lead to very serious aesthetic problems. For this reason, many authors advise against this surgical practice [6; 7; 8]. However, the bone resorption that occurs in the months following the extraction of a dental element has been the subject of numerous studies [6]. There is a difference between aesthetic and non-aesthetic zones in terms of clinical recommendations. More attention has been paid to the aesthetic zone in relation to bone resorption around the implant [9]. However, other authors have described the correlation between bone resorption. the surgical and prosthetic techniques employed [10; 11], and the timing of the insertion of the implant [12; 13; 14]. Many authors have focused to a greater extent on how to fill the socket and which biomaterial to use to avoid bone resorption after extraction and to obtain bone in the socket with good gloveless properties and good quality [15; 16; 17; 18; 19; 20; 21]. The authors of these papers [22] studied many types of biomaterials, but no studies seem to report a material that is better than the others, with the exception of autologous bone or homologous dentine taken from a patient intraorally; other authors have argued that biomaterials may be capable of supporting or even promoting the formation of alveolar bone, effectively avoiding the possibility of resorbed sockets and sockets unsuitable for the insertion of implants. However, in the case of biomaterials that determine the formation of new bone, the true quality, vascularization, and, in general, cytoarchitecture of the bone are unclear [23]. The possibility of inserting an implant in compact but poorly vascularized bone does not in itself imply certainty on long-term follow-up compared to sockets with regenerated and well-revascularized bone. Therefore, obtaining regenerated bone with a cytoarchitecture similar or identical to the native type is, in fact, a guarantee of the integration of the implant and its duration over time. Some authors have highlighted the possibility of obtaining regenerated bone in the alveolus by simply inhibiting the osteocl action exerted by the periosteum by inserting a PTFE membrane between the periosteum and the cortex [24; 25; 26; 27; 28; 29]; in this technique, a non-resorbable Gore-Tex PTFE membrane placed between the bone and the periosteum in the vestibular area of the alveolus subjected to tooth extraction can inhibit reabsorption via the inhibition of the osteoclasts contained in the periosteum. For this reason, subsequently, another author described a technique that simply involves the insertion of collagen inside the alveolus and a PTFE membrane; the latter is then removed, leading to the acquisition of bone volumes of excellent quality. However, the removal of the PTFE membrane and its cost are important limitations in terms of clinical use. Other authors have modified this technique, effectively replacing the PTFE membrane with a porcine or bovine cortex membrane glued to the cortex with the human fibrin glue Tisseel [27; 28; 29; 30; 31; 32] or with the application of a biodegradable magnesium membrane [33]. The use of collagen inside the alveolus together with this type of technique led to the authors' excellent clinical results [34].