Review - ZZI 04/2016

The use of allogeneic bone grafts for pre-implant alveolar ridge augmentation

Elmar Esser1, Stefan Hümmeke1, Mischa Krebs2, Frank Maier 3

Summary: Processed bone allografts (FDBA/DFDBA) are associated with a minimal risk of viral and non-viral transmission and do not trigger any clinically significant immune reaction. Clinical, histological and histomorphometric results in the literature and in our own experience are comparable to results with autologous bone grafts. The success of the clinically similar handling mainly depends on the soft tissue management. The main problem with both techniques is dehiscence, which may be positively influenced by resistant collagen barrier membranes. The unlimited availability, the avoidance of bone harvesting and the possibility of standardization and easy adjustment to the bone defect are major advantages in the case of severely resorbed alveolar ridges. In our opinion, processed bone allograft prior to implant placement is clinically equivalent to avascular autografts with far superior handling.

Keyword: Ridge augmentation; allogeneic bone augmentation procedures; bone grafting, dental implants; customized allogeneic bone blocks; allogeneic frame technique; guided bone regeneration with particulate allograft

Cite as: Esser E, Hümmeke S, Krebs M, Maier F: The use of allogeneic bone grafts for pre-implant alveolar ridge augmentation. Z Zahnärztl Implantol 2016; 32; 284–296

DOI 10.3238/ZZI.2016.0284–0296

Introduction

The Brånemark protocol has revolutionized rehabilitative dentistry. Increasing experience has resulted in significant extensions in the indications with remarkable reductions in the contraindications. This development has been marked by augmentation techniques, albeit involving additional burdens and risks as well as prolonged treatment times. With the current opposite trend toward minimally invasive and non-augmentative methods, discussion is currently focused on the “classic” augmentation techniques with autologous material and comparatively high expense.

Autologous bone

Autologous bone block grafts have been regarded to date as the first choice in sites subject to mechanical stress. Even though it may be assumed that transplanted osteoblasts become necrotic after an ischemia time of > 24 h [8], their cell contents and the non-collagen bone matrix possess osteoinductive potency on account of growth and differentiation factors, unlike other bone substitute materials. Particulate autografts do not exhibit adequate mechanical strength and therefore require stabilizing membranes or shell techniques.

Bone blocks are usually taken from the retromolar region, the mandibular symphysis or the pelvis. Harvesting is inevitably associated with donor site morbidity, which is estimated at 19.4 % for the iliac crest [15] and 5.6 % for the mandible [40]. Grafts obtained intraorally are limited with regard to their maximum volume (retromolar: c. 40×15×5 mm/chin: c. 25×15×10 mm) and contour and adaptability to the defect.

Augmentation techniques in the alveolar ridge

There are no confirmed data regarding a methodological advantage for a “standard” technique of alveolar ridge augmentation [5, 11, 17]. Only sinus floor procedures can be regarded as largely resolved, regardless of the employed material and technical operative details [3]. At most, the use of a membrane in the transmaxillary approach through the canine fossa is still controversial [16]. In this connection, there is no evidence that autologous material offers an advantage compared with other substitute materials [4, 11, 25, 34, 46]. The present study therefore excludes assessment of allogeneic bone material in conjunction with sinus floor augmentation and refers exclusively to pre-implant augmentation of the defective external alveolar ridge.

Onlay block transfer, distraction osteogenesis, GBR techniques and interposition grafts have been introduced for vertical augmentation of the maxilla and mandible. All these methods are regarded as user- and technique-sensitive. Use of autologous material is associated with bone harvesting and secondary morbidity. Autologous blocks must be precisely tailored to fit the defect. Allogeneic bone provides the option of a simplified and standardized technique with shorter operating time and individually prefabricated grafts.

Allogeneic bone preparations

Allogeneic bone is derived from living or cadaver donors and, like blood and blood products, it carries infection risks. Vital bone cells and non-collagen bone matrix induce cell-mediated antibody reactions. The infection risks can be reduced to a calculated minimum by donor selection, serological tests and processing and sterilization methods. The risks of an antigen-antibody reaction are diminished to a subclinical level by processing and preservation methods [19]. Three different allogeneic bone preparations are licensed in Germany for oral surgical indications, differentiated according to preservation method:

Cryopreserved bone allograft (CBA): living or cadaver donor with validated sterilization method (in the past treated only with an antibiotic cocktail)

Freeze-dried bone allograft (FDBA): living or cadaver donor with validated sterilization method

Demineralized freeze-dried bone allograft (DFDBA): living or cadaver donor with demineralization and validated sterilization method

All product lines are available as blocks (cortical, cancellous) or as chips or granules (cortical, cancellous). FDBA is also produced as a bone ring and DFDBA in the form of a cortical chip 1–3 mm thick or granules (DBM).

Fresh frozen bone allograft (FFBA), only frozen after harvesting and usually treated only with antibiotics, largely corresponds to the raw material according to biomechanical criteria and so contains growth and differentiation factors. Simpson et al. have demonstrated vital cells in FFBA [43]. The method therefore has a typical increased risk for virus transmission [49]. There are many reports in the international literature of very good results with FFBA, a bone preparation not licensed in Germany [1, 2, 9, 12, 13, 35, 36, 39, 44]. Critics of allogeneic bone transfer frequently and wrongly base their rejection on the infection risk of FFBA without considering the validated processing of FDBA and DFDBA, products licensed under the German Medicines Act (AMG) [19].

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