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Histomorphometric and Clinical Analysis of Ridge Preservation Procedures in Extraction Sockets with Buccal Bone Defects (>5 mm) Using an In Situ Hardening Biphasic Calcium Phosphate (HA/\(\beta\)-TCP) Graft and a Bioresorbable Matrix: A Human Study at 6 Months  
[PERSON] 1,1, [PERSON] 2,*,  
changes [1]. These changes to the alveolar ridge consist in the highest amount of horizontal bone loss with a concomitant vertical ridge height loss, which has been recorded to be more prominent at the vestibular site. The findings from a recent systematic review evidenced that the horizontal bone loss, ranging between 29% and 63%, was higher than the vertical bone loss, ranging between 11% and 22%, at 6 months after dental extraction [2]. Multiple key factors seem to be involved in this tissue shrinkage, and the most important role seems to be played by bundle bone resorption and blood clot stabilization [2; 3; 4]. These three-dimensional tissue changes can result in difficulties in performing a prosthetically-driven implant placement leading to prosthetic compromises. An adequate architecture of the alveolar ridge volume seems to be one of the most important key factors to obtain successful esthetic implant-supported restorations [2; 5]. Consequently, in-depth knowledge of post-extraction healing patterns and contour changes can be essential for a correct implant treatment planning. It has been well determined that the soft tissue morphology around implants is related to the underlying bone topography; moreover, the buccal bone plate can affect the stability of peri-implant soft tissues around implant restorations [6; 7]. Furthermore, a reduced thickness of the vestibular bone plate might induce midfacial recession of soft tissue, which is considered a very common cause of esthetic failure in implant-supported rehabilitation [8]. The ridge preservation technique includes all procedures that maintain the alveolar volume within the soft and hard tissue socket existing at the time of extraction [9]. This procedure is suggested when implant insertion is not possible at the time of extraction, when implant primary stability cannot be achieved or when there are absolute contraindications to implant treatment. The preservation of the alveolar volume using bone substitutes in fresh extraction sockets, minimizes bone resorption and facilitates subsequent insertion of a dental implant. This improves esthetic and functional criteria, reducing the need of additional bone grafting surgeries at the time of implant placement [10]. Several techniques and biomaterials have been proposed over time, including fresh extraction socket grafting with a bone substitute, occluding the access to the socket with a resorbable barrier, overbuilding of the vestibular bony wall, or a combination of some of them, with or without primary intention healing [4]. However, no significant clinical or histomorphometrical differences have been evidenced between the various bone substitutes, although collagen alone has been demonstrated to be unable to reduce tissue changes after tooth extraction [1; 4; 11]. Resorbable collagen membranes and bovine-derived xenografts is one of the most common combinations for treatment, since it has been found to be effective for bone regeneration around implants, alveolar ridge augmentation, and alveolar ridge preservation [12; 13; 14; 15; 16]. However, some randomized controlled clinical trials have also found promising outcomes for calcium phosphate alloplastic graft materials in terms of new bone formation and preservation of the alveolar ridge volume [17; 18; 16]. Synthetic calcium phosphate ceramics are widely used because they are similar to human bone, which is principally composed of calcium phosphate hydroxyapatite [1; 16]. Calcium phosphate-based bone grafts are osteeconductive and free of any infection risk compared to animal-derived xenograft or allograft.