## 1 Introduction  
Implant dentistry has transformed rehabilitation treatments, bringing an enhancement to patients' life quality. A suitable height and width of the bone site are parameters required to perform dental implant placements. There are several techniques to restore the amount of bone loss; for example, the split crest method [1], bone-graffing strategies [2], or guided bone regeneration (GBR). GBR is widely used in oral surgery and implantology. It is based on employing a membrane to bypass non-osteogenic cell invasion in the bone healing area, dispersing every bone regeneration interference. Thus, only osteoprogenitor cells can reach the bone defect site [3; 4; 5]. According to [PERSON] et al., \"additional bone augmentation was indicated in more than 50% of cases\" of implant placement, and GBR was the most common technique performed [6].  
Indeed, a fundamental aspect of GBR is the membrane used. Membranes' properties are closely connected with their materials and structure. Therefore, ideal features should be biocompatibility, integration capability with native tissues, stopping other cell invasions, keeping space for blood clot organization, easy clinical management, adequate stiffness, and plasticity to withstand the compression of the overlying soft tissue [7; 8; 9; 10; 11; 12]. Membranes can be divided into two generations: non-resorbable membranes, mainly polytetrafluoroethylene (PTFE) in its expanded form (e-PTFE); and resorbable membranes, including collagen forms [13; 14; 15; 16]. On the one hand, non-resorbable membranes offer the clinician a shaping site chance and a good barrier effect thanks to a metal core; on the other, they have to be suddenly removed if they are exposed before the healing process ends due to bone infection risk, and they also need a second surgery to be excised. Instead, there are resorbable barriers derive from animals. They should reabsorb in a couple of months due to hydrolysis or enzymatic degeneration, so they have a restricted power in stopping epithelial cell invasion and do not provide a space-making effect because they do not have a metal core. However, there is a low infection risk related to unwanted exposure, and they do not need surgery to be removed.  
Nevertheless, collagen membranes overcome their lower space-making effect due to the current technique by the addition of a bone graft into the defect to create a scaffold easily colonizable by desired bone cells. Collagen-based membranes can be obtained from human skin, bovine Achilles tendon, porcine skin, and porcine inner organs [17]. This kind of barrier has different degradation times depending on the animal source, and it means that they could be reabsorbed before the optimal tissue maturation period. Several bioengineering methods are recommended to avoid this adverse event; for example, cross-linking with chemical agents such as glutaraldehyde, genipin, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), or ultraviolet radiation. Despite the collagen stability improvement after chemical treatment, residues of these agents are responsible for inflammation in the site of placement [18].  
Another fundamental characteristic of membranes is the porosity of the structure. It is suggested that the pore size directly influences bone regeneration capability. With that, a better occlusivity towards soft tissue cells can be ensured [19].  
Membrane properties are so crucial that the third generation with biologically active components is under development, such as a delivery medium for growth factors and antibiotic molecules [20]. The present study aimed to investigate the membrane's outcomes for bone regeneration procedures in quantitative and qualitative effectiveness during translational evaluations performed Italian Implant Retrieval Center over 30 years.