Corticocancellous Fresh Frozen Allografts Bone Blocks for Augmentation of Atrophic Posterior Mandible. Case Series. Clinical, Histomorfometric and Tomographic Study in Humans

Residual bone ridge atrophy in the posterior mandible is a clinical challenge for dental implants placement. Among several techniques used to solve this situation, onlay autogenous bone graft usually harvested from the iliac crest,  interposicional grafts, bone distraction and nerve lateralization are the most performed. However these techniques present some disadvantages such as morbidity, increased surgical time and costs. As an alternative, the use of allograft can be considered. There are advantages such as reduction of surgical time, unlimited bone quantity, and decreased morbidity.

The aim of present the study was to evaluate clinical, histological, histomorphometrical and tomographical aspects of fresh frozen bone allograft used to augment atrophic posterior mandible bone ridges to allow placement of dental implants.

Sixteen hemi-mandibles of 12 patients (4 patients treated bilaterally) presenting critical alveolar atrophy were three-dimensionally reconstructed using cortico-cancellous fresh frozen allograft bone blocks deriving from distal femoral head . A total of 30 blocks were fixed with titanium 1.5mm screws and covered with particulate bovine bone mineral and collagen membrane. After six months, implants were inserted and bone biopsies were harvested and sent for histological and histomorphometric analysis. Bone samples were either embedded in paraffin, prepared for hematoxylin and eosin staining procedure or in resin to use a sawing and grinding technique  (Exakt - Germany), prepared for alizarin red and Stevenel's blue staining. Computed cone beam tomography scans were taken both at immediate postoperative bone grafting and previously to implant placement (6 months after grafting), in order to evaluate volumetric analysis (Mimics - Belgium). Dental implants were observed after prosthetic rehabilitation. ANOVA, Pearson correlation, Kruskal-Wallis, Mann-Whitney, and Tukey statistical tests were used.

Thirty blocks were distributed between 9 female and 3 male patients, aged between 37 and 64 years (mean 50.9 ± 8.3 years). Each patient received 1 to 5 blocks (2.5 ± 1.5) under local anesthesia. Four blocks presented small wound dehiscence 15-21 days after surgery, treated with necrotic soft tissue removal followed by chlorhexidine 0.12% irrigation, and local gel 2% twice a day for 2 weeks until total closure.  A total of 32 implants were installed with follow-up from 12 to 31 months (22 ± 6,8 months) . One implant was lost within the first year. Implant survival rate was 96.9%. Age did not influence the absorption of the grafts in relation to volume (r = 0.18), height (r = 0.24) and thickness (r = 0.05), and the mean of volume absorption was 45% ± 14%. Volume resorption was similar regardless different blocks volumes (r = 0.76). Initial bone high augmentation was 4.37 ± 2.05 mm. Average of bone high gain after 6 months was 2.54 ± 1.95 mm (vertical resorption rate 48 ± 24% , p < 0.05). Graft thickness was 6.05 ± 1.73mm initially and decreased to 4.82 ± 1.68mm after 6 months (horizontal resorption rate 20 ± 18 %, p <0.05). Histology demonstrates newly formed vital bone in contact to residual acellular allograft bone, and connective tissue. There was no evidence of inflammatory infiltrate. The histomorphometric analysis showed 17.78% of newly formed bone, 29.59% allograft residual bone and 52.63% of connective tissue.

Fresh frozen allografts were biocompatible and osteoconductive permitting new bone formation. Despite bone resorption, it was possible to insert dental implants and prosthetic rehabilitation in a short term follow-up.

Deluiz D. et al. Time-Dependent Changes in Fresh-Frozen Bone Block Grafts: Tomographic, Histologic, and Histomorphometric Findings. Clin. Implant Dent. Relat. Res. 2013 Jul 9. (epub ahead of print).

Nissan J. et al. Histomorphometric analysis following augmentation of the posterior mandible using cancellous bone-block allograft. J. Biomed Mater. Res. A. 2011 Jun 15;97(4):509-13.