When correlating the clinical results and the histological outcomes, there was a positive association between the presence of soft tissue dehiscence with CCXBB exposure and a diminished amount of new mineralized bone (p = 0.06). This lower amount of new bone within the xenogeneic graft suggests a lack of full graft integration and diminished vascular supply, what may have caused the soft tissues dehiscence. Similarly, the biopsies from patients who lost their implants had a statistical significant lower amount of MVB and a statistical significant larger proportion of connective tissue, what suggests that there is a direct relationship between the primary healing of the bone replacement graft, its integration with native bone and its healing to provide a biological base for dental implants to osseointegrate. These results corroborate the importance of minimal trauma during surgery, establishment of primary implant stability and avoidance of infection and micromotion during healing as key prerequisites for achieving dental implant osseointegration [29, 30]. In fact, the high incidence of early implant loss (29.2%) reported in this clinical study, is clearly higher when compared with epidemiological data from Sweden reporting early implant loss in 4.4% of patients and 1.4% of implants [31]. The delayed bone proliferative phase has also been described associated with other bone replacement grafts for bone regeneration [32] and with demineralized bovine bone mineral (DBBM) in the healing of fresh extraction sockets [33].

A high incidence of soft tissue dehiscence and implant failures has been reported in patients receiving fresh frozen allogeneic bone grafts for reconstructing severe alveolar atrophies (36.8% incidence of dehiscence and 31.5% incidence of implant loss) [34] and 21% of implant loss [35], respectively. With the use of a different equine bone block, a previous publication reported total removal of the graft in 50% of the patients and in 20% of them the implants failed [36]. The high incidence of soft tissue dehiscence occurring in this clinical study may also be explained by the extreme narrow crestal defects (mean crestal width of 2.78 mm) multiple teeth absence and non-containing defects, what needed in most of the cases to use more than one block graft. In fact, there was a positive correlation between the number of blocks used and the incidence of soft tissue dehiscences. The use of large grafts or more than one graft may have hindered an appropriate blood supply or colonization of the graft material with bone-forming cells [37].