# The \"Sling\" Technique for Horizontal Guided Bone Regeneration: A Retrospective Case Series
## 1 Introduction  
The resorption and remodeling of the alveolar ridge in the maxilla and in the mandible are a consequence of tooth loss [1, 2, 3, 4]. Two-thirds of this reduction occurs within the first 3 months; within 1 year, the clinical width of the alveolar ridge is reduced by approximately 50% [1, 2, 3, 4]. The mean vertical loss of tissues at single extracted sites ranges from 1 to 4 mm, depending on the site location [1, 2, 3, 4]. This physiologic phenomenon occurs at different rates and degrees among various individuals and, in a few cases, it can be very pronounced. This localized alveolar bone resorption may affect the possibility of placing dental implants and their aesthetic outcome, particularly in aesthetic areas and in those patients exposing visible portions of gums when speaking and smiling. Several authors have described and developed classifications for the different types of bone defects in dedentulous patients, e.g., horizontal, vertical and a mix of the two dimensions [5, 6]. To functionally and aesthetically rehabilitate these patients with dental implants, many bone grafting techniques have been developed [7]. Many studies had shown that bone augmentation in a horizontal direction is more predictable than procedures aimed at augmenting bone in a vertical direction [8]. In particular,peri-operative complications for vertical augmentations range from 30 to 40% [8; 9]. A meta-analysis reported a complication rate of 17%; however, in general, complications in the scientific literature are under-reported [10]. There are many proposed techniques for horizontal bone augmentation. It is possible to resort to the use of a bone block graft, which can be digitally designed with modern CAD/CAM technologies as described by [PERSON] et al. [11], or a particulate bone graft. Guided bone regeneration (GBR) is one of the most widely used procedures [8]. In GBR, particulate autogenous bone or bone substitutes (they can also be mixed) are positioned in the recipient bed and kept in place by purposely designed membranes of other substances, e.g., zirconia or titanium meshes [12]. Currently, bone grafts represent the gold standard in augmentation procedures, but alternative methods such as natural polymers have been proposed as materials capable of stimulating bone regeneration. According to a recent study, the combination of multiple biomaterials guarantees better physical and biomolecular characteristics than the use of biocercamics or polymers alone. Natural composites have significant potential as an effective bone scaffold to repair alveolar defects after a tooth extraction [13]. Another natural polymer useful in oral surgery is collagen, one of the most common materials for resorbable membranes [14]. The main purposes of the membrane is to isolate the bone graft from the soft tissues that, by being faster growing, could infiltrate the particulate bone, negatively interfering with the formation of new bone and the stabilizing of blood clots. Initially, membranes were of a non-resorbable type and were usually made of various types of polytetrafluoroethylene known as Teflon and abbreviated as PTFE. Subsequently, various types of resorbable barriers--either collagen-based or of animal origin, or synthetic, usually made of polylactic acid (PLA) or polyglycolic acid (PLGA)--were developed. Resorbable barriers were developed for two main reasons: there was no need for a second surgery to remove a resorbable membrane and there was a clinical impression that complications from non-resorbable barriers could be reduced in both number and severity. It has been proven that when a post-operative dehiscence occurs in an area under GBR, the clinical outcome is less favorable [15]. The use of blood derivatives such as PRP and PRF give the possibility of dealing with this complication, supporting the healing and regeneration of the site [16; 17].