# Fresh Frozen Allogeneicic Bone Block in Maximly
## 4 Discussion  
Allogeneic fresh frozen bone (FFB) has been widely used for years in orthopedic reconstructive surgery and reported to have different successful applications in the oral and maxillofacial district, including ridge augmentation [29; 30; 31; 32], reconstruction of large post-traumatic or post-oncologic defects [33; 34; 35], and sinus floor elevation [36; 37; 38; 39; 40]. FFB is osteeconductive and weakly osteoinductive, and its main advantages compared to the autogenous bone are its unlimited availability coupled with the lower morbidity for the patient, with no necessity of second surgical site to harvest the graft. Main concerns related to the use of FFB, even if remote, are the possible risks of cross-infection [41; 42] and immune response complications [43; 44]. The current study reported, for the first time, histomorphometric and SEM analyses performed on a bone specimen harvested 15 years after maxillary sinus augmentation with FFB block. The main interest of these results is represented by the exceptional duration of the follow-up, allowing to evaluate the percentage of vital bone and residual FFB 15 years after the grafting procedure. Conversely, the availability of a single specimen expresses the weakness of the present results; thus careful conclusions should be drawn. The biopsy analyzed in the current investigation showed 15.4% residual graft particles (RG). This finding is in agreement with a recent study of [PERSON] et al. [45], in which biopsies from ridges augmented with FFB blocks were retrieved four (24.3% RG) and six months (18.4% RG) after grafting. These data, even if they should be interpreted with caution, seem to indicate that the greatest part of graft remodeling and resorption takes place in the first period after the surgical procedure, likely as a consequence of the healing process. Then, after a second possible biological boost for the remodeling process given by the second surgical trauma (implant placement), no further modifications in terms of graft resorption seem to occur over time. Moreover, the absence of osteoclasts in our specimen is indicative of a bone site with low turnover. However, no inflammatory cells or infiltrate were detected, suggesting a good integration of FFB, which appeared well integrated with the newly-formed bone (NFB) without discontinuities between the two components under optical and scanning electron microscopy. Only different staining affinity and electron uptake (together with the presence of empty osteocytic lacunae) revealed their origin. In recent systematic reviews [46; 47], autogenous bone (AB), when used as a grafting material in the maxillary sinus, promote the highest percentage of NFB in comparison to the other bone substitutes. However, implants placed into sinuses grafted with AB exhibited a lower survival rate compared to sinuses grafted with other bone substitutes. This finding has been attributed to the AB high resorption rate. [PERSON] and coworkers confirmed that AB presents one of the greatest volumetric contraction among the various bone substitutes, followed by allografts [48]. According to the different formulations of allograft (demineralized freeze-dried bone allograft, mineralized freeze-dried bone allograft or FFB), different behaviors in the maxillary sinus have been reported, probably with higher resorption rate and lower volumetric stability for demineralized allografts, even if associated with an increased osteoinductive potential related to the direct effect of growth factors [49; 50]. FFB blocks were associated with satisfactory volumetric bone maintenance, even in more challenging regenerative procedures, such as posterior mandible augmentation [51]. EDX analysis allowed us to estimate the chemical composition of the two bone compartments (NFB and RG). Apparently, even if non-vital, RG particles resulted comparable with NFB in terms of Ca++ and P++ contents.