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].

Mineralized and demineralized freeze-dried bone is sterilized and freeze-dried in a validated process. The product of licensed manufacturers is a medicinal product under §§ 13/21 AMG based on manufacturer’s permit and marketing authorization. Accordingly, medicinal products must be biologically safe and therapeutically suitable based on testing by the Paul Ehrlich Institute. Table 1 provides a summary of the manufacturers of bone preparations licensed in Germany according to the Medicines Act (AMG).

We have previously shown the safety of processed allogeneic grafts using the example of peracetic acid-sterilized allografts [19]. Despite the finding of a low DNA concentration in allografts [20, 21] and the fundamental possibility of a T cell-mediated immune reaction, there has been no known clinically significant HLA sensitization or HLA antibody production so, according to current knowledge, the antigenic relevance can be estimated as at most subclinical or insignificant as induction of antibody production against HLA antigens falls considerably below the threshold [19].

Clinical results with processed allogeneic block grafts (FDBA)

The advantage of allogeneic bone consists in the fact that its ready-to-use availability is largely unlimited while providing favorable conditions for simplifying standardization for both block transfer (preoperative figuration via CAD/CAM process) and for shell techniques. Recent review articles [4, 6, 32] confirm high success rates using case series though they also refer to the as yet low level of scientific evidence. However, this critical assessment is quite applicable to scientific knowledge of autologous reconstruction methods also.

Different recipient and donor regions, the augmentation vector (onlay vs. veneer), different defect geometry, bone quality and consistency (block vs. particulate), supportive measures (resorption protection, shell techniques), implantation timing and soft tissue status (thickness, perfusion) make objective evaluation difficult. Therefore, autologous alveolar ridge augmentation is not yet adequately confirmed by long-term studies and is regarded as technique- and user-sensitive [3]. Under this aspect, all methods that reduce the technical complexity and/or have standardizing effects offer a clinically relevant prospect. In this regard, GBR techniques and bone substitutes have gained in importance, competing with the exclusive use of autologous bone [4, 25, 42].

Of the recent review articles [6, 32, 47] only that by Waasdorp and Reynolds [47] considers the different allogeneic product lines: processed, sterilized, freeze-dried bone (FDBA) v. fresh frozen, nonsterilized bone (FFBA) and lists only 7 publications with 124 allogeneic block grafts (FDBA) for preimplant onlay or inlay bone grafting of the maxillary and mandibular alveolar ridge. The rate of block loss is 8.5 % and the implant success rate is 99.9 % with a follow-up interval of at least one year after bone transfer. The limited histological examinations indicate adequate new bone formation without inflammatory reactions. The block transfer technique corresponds to the familiar procedure using autologous material. Most users cover the blocks with an absorbable membrane. In 3 of 7 studies, platelet rich plasma (PRP) is used in addition.

For 60 purely cancellous FDBA blocks in the anterior maxilla, Chaushu and Nissan [10] found a graft loss rate of 4.4 %, bone gain of 5 ± 0.5 mm in the horizontal and 2 ± 0.5 mm in the vertical dimension, a resorption rate of 0.5 ± 0.5 mm at implantation and 0.2 ± 0.2 mm horizontally at implant uncovery with an implant survival rate of 95.6 %. By contrast, cancellous block grafts in the posterior mandible showed a much higher rate of loss of 20.7 % with an average gain in height of 4.3 ± 1.6 mm and a resorption rate of 5 %. Keith et al. [26] and also Plöger and Schau [38] found that total losses were clearly greater in the posterior mandible with a rate of allogeneic block loss of 8.5 % and 9.5 % respectively. All complications usually occurred during the early healing period in the form of wound dehiscence and exposure with subsequent infection of the graft.

The review article by Monje et al. [32] found calculable and stable results for block transfer in the maxilla without taking the allogeneic subtype (FDBA/FFBA) into account, with a loss rate of 2.5 %, an average resorption rate von 21.7 ± 30.5 % and an average implant survival rate of 96.9 %. Histological examination showed a surprisingly high proportion of newly formed bone (62 ± 11.8 %), surrounded by non-vital remnants of the allograft with empty lacunae, especially in the central region. The histomorphometric results obtained by Chaushu and Nissan [10] with cancellous FDBA blocks were characterized by less bone formation in the maxilla: 33 ± 18 % newly formed bone and 26 ± 17.8 % non-vital elements. The proportion of new bone formation tended to be higher in younger patients (< 40 years), bore no relation to the use of a membrane and was even comparatively more pronounced in the posterior mandible at 44 ± 28 %.

The vertical augmentation with ring-shaped autologous bone grafts described by Giesenhagen [23] has now been extended to processed allogeneic bone rings [50]. The method has so far been verified only by case descriptions, however. In a prospective randomized comparative study with interposed autologous versus allogeneic blocks in the postforaminal mandible (sandwich technique), Laino et al [28] found no significant differences with regard to the rate of new bone formation, along with similar clinical results. However, a higher percentage of residual bone was detectable in the alloblock. Abundant newly formed bone was apparent histologically, with direct contact between the allograft and regenerated bone without connective tissue interposition.

In summary, in line with our own experience [31], we regard FDBA alloblocks as very suitable for reconstructive preimplant procedures in the alveolar ridge (Fig. 1). The average rates of graft exposure, delayed wound healing and graft loss and the degree of resorption and substitution are similar to the results with autologous techniques. This also applies for the distinction between onlay and inlay grafts, which is relevant for prognosis, and for regional classification (increased risk in the postforaminal mandible). Different biological behavior is apparent, depending on bone density. Cancellous blocks show faster integration, a lower rate of impaired wound healing and, due to faster vascularization, better results in the event of removal of superficial necrosis and secondary healing associated with management of complications. However, they are also characterized by a higher resorption rate compared with cortical blocks. If cortical parts are exposed and if the cancellous bone is shielded from oral bacterial invasion, partial augmentation success can be achieved even in the absence of granulation (Fig. 2).

The familiar technique and user sensitivity of the block transfer can be substantially reduced by preoperative figuration via CAD/CAM [24, 41]. In this connection, it can be observed that a preformed individualized block graft not only standardizes and shortens the operation but also achieves faster vascularization and bone substitution on account of the extensive degree of adaptation (Fig. 3).

Clinical results with particulate material (FDBA/DFDBA)

Frame techniques

With a frame technique using DFDBA/FDBA granules and an resorbable PGA/TMC shell, Geurs et al. [22] found an average gain in width from 2.4 to 5.2 mm with 21 % newly formed bone. Toscano et al. [45] obtained an average gain in width of 3.5 mm with a similar technique. Walloway and Dorow [48] contour a cortical frame from an FDBA block, which is filled with FDBA cortical granules following screw fixation. In the three cited studies, secondary implantation is performed. Esser and Schmidt [18] use demineralized bone matrix (DFDBA) as frame, which becomes flexible and therefore easily adaptable and fixable following rehydration. The frame is filled with FDBA cancellous granules and covered crestally with an resorbable membrane, as in the previously cited methods [22, 45, 48]. Esser and Schmidt [18], however, place implants simultaneously when the bone width is reduced to 2–3 mm and report a gain in width of 4–7 mm, an impaired wound healing rate of 3.8 % and an implant loss rate of 4.7 %. In the case of combined defects with horizontal and vertical augmentation, however, secondary insertion of the implants is performed (Fig. 4).

GBR membrane techniques

In the case of smaller defects bounded by teeth, simultaneous implantation and augmentation with shell techniques is more difficult on account of placement of fixation screws. In these cases, we favor GBR membrane techniques using stable collagen membranes. Le and Borzabadi-Farahani [30] in a prospective study found complete (61.1 %) and much improved (35.2 %) correction of vestibular dehiscence defects in the posterior maxillary or mandible with simultaneous implantation and GBR technique using FDBA cortical granules and a cross-linked collagen membrane. The results were recorded objectively by means of DVT scan. The definitive effects of treatment showed a significant relationship with the size of the defect. Vertical deficits of > 5 mm were treated only 90 % with a resulting disturbance of contour but without requiring further corrective measures. The cumulative implant and graft success rate was 98.1 %. Two patients suffered impaired wound healing with graft exposure, though uncomplicated secondary wound healing occurred in one case. This corresponds to our experience with exposed cancellous granules, which usually exhibit a surprisingly positive tendency to spontaneous healing after superficial removal.

Beitlitum et al. [7] achieved an average vertical bone gain of 3.5 mm (SD ± 1.2 mm) and horizontal gain of 5.0 mm (SD ± 1.3 mm) with FDBA granules and cross-linked collagen membrane. Additional application of autologous bone chips obtained with the Safescraper did not show any significant improvement. The membrane exposure that occurred in 14 % with horizontal and in 10 % with vertical augmentation proved to be the only statistically significant prognostic parameter for the final augmentation effect.

Le et al. [29] describe a case series using a „tent pole technique”. In this, vertical defects were filled with particulate FDBA material with an average gain in height of 9.7 mm. The rate of wound dehiscence and implant loss requiring a second augmentation procedure was 26.6 % and 13.3 % respectively. Histomorphometric analysis at the time of secondary implantation showed an average proportion of newly formed bone of 47 %. Langer et al. [27] reported good long-term results in a small case series after vertical augmentation with the GBR technique and particulate DFDBA.

Discussion

Allografts in conjunction with implant-based rehabilitation are currently controversial. Only processed allogeneic bone (FDBA/DFDBA) is licensed in Germany as a medicine. The safety risk regarding viral infection can be regarded as extremely low and the hypothetical risk of an antigen-antibody reaction as not clinically significant [19].

Processed allografts deliver similar results to autologous material, while the technical operation requirements are identical. According to Chiapasco et al. [11] a partial and total rate of loss of 3.3 % and 1.4 % and an implant loss rate of 8.5 % can be assumed for autologous block grafts. In their comprehensive search of the literature, Jensen and Terheyden [25] found an average gain in width of 4.4 mm and a complication rate of 3.8 % for horizontal autologous block transfer for locally limited defects, and for vertical block transfer, they recorded an average gain in height of 3.7 mm with a complication rate of 29.8 %. Pommer et al. [37] also report similar results based on literature reviews. According to this, autologous onlay grafts achieve an average horizontal and vertical bone gain of 5 mm and 4 mm respectively and have a resorption rate of 22 % and 38 %, a complication rate of 4 % and 30 % and an implant loss rate of 1 % and 15 % respectively. Based on a limited evidence level, clinical data show similar results for FDBA blocks with an incorporation rate amounting to about 90 %, a new bone formation rate at the time of re-entry of approximately 30 %, with delayed incorporation and slower remodeling [4, 10, 33, 47], dehiscence rates of c. 15 % and total and partial loss rates of 5 % and 4 % respectively.

Apart from their technical complexity, augmentation procedures are characterized primarily by impaired wound healing in the region of the incision line. In the event of exposure, the prognosis of the graft depends almost exclusively on the degree of vascularization and possibly by cortical coverage. In this connection, exposed fine granules and cancellous bone blocks demonstrate a quite good tendency to secondary healing with normal secondary granulation after removal of superficial necrosis. Because of a dehiscence rate < 10 % we recommend the use of a stable collagen membrane with cancellous bone block transfer also. With cortico-cancellous blocks, on the other hand, the collagen membrane can be omitted.

Besides the almost unlimited availability, alloblocks offer the possibility of congruent prefiguration via CAD/CAM methods following 3D evaluation of the alveolar ridge defect. Congruent adaptation to the defect with multipoint gap-free contact simplifies the operation and reduces perioperative stress while providing much better conditions for vascularization. We therefore consider that the prefigured alloblock (Fig. 3) has considerable, as yet inadequately confirmed potential compared with the freely fitted autoblock, especially in the postforaminal mandible.

Avoidance of a harvesting operation also results in a considerable time saving for shell and tent pole techniques using FDBA granules. Naturally, autologous material is the method of first choice, especially for small amounts and when sufficient is available in the vicinity of the primary operation area. From clinical aspects, we regard processed allografts as an optional alternative to avoid complex harvesting procedures and for standardization, with shortening of the operation time and reduction of perioperative stress.

Conflict of interest: The authors E. Esser, M. Krebs and F. Maier have acted as consultants to Argon Medical GmbH & Co. KG., Bingen, which markets the bone preparations of DIZG (gemeinnützige Deutsche Gesellschaft für Zell- und Gewebeersatz [the non-profit German Society for Cell and Tissue Replacement], Berlin). The author S. Hümmeke reports no conflict of interest.

Addresses for correspondence:

Prof. Dr. Dr. Elmar Esser,

Dr. Stefan Hümmeke

Oralchirurgisches Centrum Osnabrück

Hans-Wunderlich-Str. 5

49078 Osnabrück

e.esser42@googlemail.com

Footnote

1 ICOS Implant Centrum Osnabrück

2 Políklinik für Zahnärztliche Chirurgie und Implantologie, J.-W.-Goethe-Universität Frankfurt/M., Praxis Dres. Krebs, Alzey

3 Zahngesundheit im Loretto, Tübingen

Übersetzung: LinguaDent

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