Proper implant treatment planning has become an essential part of the prosthetic reconstruction of lost dentition.1 Unfortunately, ridge resorption is an unavoidable physiological process associated with tooth loss, resulting in a residual ridge that is horizontally and vertically deficient.2–5 Augmentation of these atrophic ridges is often a prerequisite for implant placement because implants have to be placed in a prosthetically driven position, to achieve long-term stability, function, and aesthetics.6–8 Various bone augmentation techniques, such as guided bone regeneration and distraction osteogenesis, are commonly used. However, in the presence of severely resorbed ridges, block grafts are preferred.6,7 This is primarily because block grafts, being corticocancellous in nature, have the ability to maintain the 3-dimensional (3D) space needed for bone regeneration.8,9 In addition, block grafts have been found to effectively augment severely resorbed ridges for implant placement.10–14
Block grafts (autogenic,15 allogenic,7 or xenogenic16) are frequently corticocancellous or monocortical in nature. Autografts have always been considered the gold standard material because of their osteogenic, osteoconductive, and osteoinductive properties.17 However, they are available in limited quantities.18 Besides being a technique-sensitive procedure, significant morbidity (eg, pain, edema, infection, paresthesia, loss of muscle tone, loss of tooth vitality, and gingival recession) is associated with common intraoral donor sites like the chin and mandibular ramus.18,19 Therefore, to counteract these limitations associated with autogenic block grafts, allogeneic block grafts have been developed.7,20
The 3D block technique, which utilized block allografts, was first proposed as a biphasic surgical approach in 2006.21 First, a cone beam computed tomography (CBCT) scan of the surgical site is obtained. Second, a sterile prototype of the recipient bed is fabricated from information extracted from the CBCT scan. Third, the block allograft and membrane are adjusted on the sterile prototype and subsequently fixated onto the recipient bed. In this technique, allogeneic block grafts (Puros J-Block; Zimmer Dental, Inc, Carlsbad, CA) were obtained from femur heads and treated by a patented procedure known as the Tutoplast process. The allografts are subjected to solvent dehydration and gamma irradiation, which not only sterilize the allografts but also maintain the mineralized structure and organic matrix.20 Therefore, predictable bone and periodontal regeneration can be achieved.22,23 However, limited evidence is available to substantiate the use of this newly developed 3D block technique. Therefore, the aim of this article is to assess the clinical and histological outcomes of this technique.
Materials and Methods
Eight patients (6 men and 2 women) with a mean age of 54 years (ranged between 33 and 73 years) presented with severe ridge resorption in 1 or more edentulous sites, both in the maxilla and mandible, were enrolled in the study. These patients needed a reconstruction of the edentulous sites before implant-supported prosthetic rehabilitation could be performed. Patients with compromised systemic conditions, those who had chemotherapy or radiotherapy, or who were on bisphosphonates were excluded. Written informed consent was obtained from each patient before the start of the study. The study started on June 6, 2008, and ended on September 14, 2009. Six patients needed horizontal bone reconstruction, and the remaining 2 patients required vertical bone reconstruction.
All patients took a presurgical CBCT scan to evaluate the residual bone anatomy and plan the implant positioning. The digital data were sent to a service center that produced the synthetic prototypes of the residual ridges. The prototypes were wrapped and sterilized before the allogeneic block grafts (Puros J-Block, Zimmer Dental, Inc) were trimmed and adjusted on these models (Fig. 1, A and B). In addition, pericardium membranes (CopiOs; Zimmer Dental, Inc) were shaped over the allogeneic blocks as well as the sterile prototype (Fig. 1, C) and subsequently sealed in a sterile envelope (Fig. 1, D). As the allogeneic blocks and barrier membranes were modified to fit the recipient beds before the surgery, this saved chair time, and clinicians could concentrate solely on soft tissue management to minimize flap tension and achieve tension-free primary wound closure (Fig. 2, A–D).
All patients were prescribed antibiotics (Klacid; Abbott, Abbott Park, IL) and nonsteroid anti-inflammatory drugs (NSAIDs) (Synflex; Recordati, Milano, Italy) before the surgery. Patients were instructed to start the antibiotics 2 hours before the surgery and to continue it for 6 days after. The NSAIDs were taken for 4 days starting at the day of the surgery.
Eight months after the first surgery, the surgical sites were reentered, and the fixation screws were removed. Implant placement surgeries were performed, and bone core biopsies were obtained using a trephine drill with an internal diameter of 3 mm accompanied by copious irrigation. In sites that had horizontal bone augmentation, the bone biopsy was taken from the buccal to palatal aspect at a site that was reconstructed with a block allograft after the implants were placed. In sites with vertical bone augmentation, the bone biopsy was taken from a coronal to apical direction before the implant placement. This would allow both regenerated and native bones to be harvested in 1 bone biopsy core (Fig. 3, A–D).
The biopsies of varying lengths ranging from 4 to 8 mm were marked at one end with indelible China ink (17, Black ink; Pelikan Italia S.p.A., Milano, Italy) to correctly orient them. They were fixed in 10% formalin for 24 hours, decalcified for 6 hours, dehydrated with increasing concentrations of alcohol, embedded in paraffin wax, sectioned to 4-μm-thick histological sections, and finally stained with hematoxylin and eosin.
The histological analysis evaluated (1) the presence, quality, and quantity of the newly formed vital bone and residual graft, (2) the presence and quality of the connective intertrabecular tissue, (3) the presence of necrosis, and (4) inflammatory reaction to extraneous body (Table 1).
Upon reentry, the regenerated tissue maintained its volume, and no significant bone resorption was observed. The heads of the fixation screws were at the cortical level, indicating dimensional stability of the graft. Histologically, highly vital newly formed bone was observed in all subjects (Fig. 4, A) at 8 months after the bone augmentation surgery. The bone was mostly immature, mixed, and strictly near areas where the allograft was still present and not completely resorbed (Fig. 4, B). The newly formed bone appeared vital and was characterized by the presence of osteocytes in lacunae in the bone (Fig. 5, A). Rows of numerous osteoblasts surrounded by plentiful extracellular matrix were observed in close contact with newly formed vital bone, which showed vital osteocytes in the mineralized tissue (Fig. 5, B). The newly formed tissue had a nonorganized appearance in 6 cases, whereas in 2 cases, bone tissue with a clear lamellar pattern and multiple appositions of new vital bone was observed (Fig. 6, A and B). Residual graft particles were surrounded by the newly formed lamellar bone that usually took on a “ribbon-like” appearance following the trabecular pattern of the graft (Fig. 6, A and B). Intertrabecular areas were filled with vascularized connective tissue (Fig. 7, A). Focal areas of chronic inflammatory infiltrations characterized by the presence of lymphocytes and plasma cells were observed in 3 cases (Fig 7, B). Necrosis, foreign body reactions, and acute inflammation were not observed in these patients.
The allogenic block graft, which is made up of corticospongious, mineralized, and collagenated bone, has proven to be an effective “scaffold” for the reconstruction of severely atrophic ridge defects.24–26 The results of this study confirm the effectiveness of mineralized block allografts, as reported in the literature.20,27,28 Commercially available allogenic block grafts have several advantages over autogenic block grafts, namely, (1) the elimination of a second surgical site, (2) no donor site morbidity, (3) reduction of surgical time, and (4) less patient discomfort and stress.
Histological evidence showed that the graft was at an advanced substitution phase, with wide areas of newly formed bone, high osteoblastic activity, and rich in vital osteocytes. These are signs of active bone remodeling. Parts of the newly formed bone were in close contact with the residual graft particles and had a ribbon-like pattern along the graft. This indicated that there was a scaffolding function of the allogeneic block graft. Lamellar architecture with multiple apposition of vital bone suggested that there was substitution of the graft by the newly formed bone. The collagen component and organic matrix of the allogeneic block graft favored and accelerated the colonization of the intertrabecular areas by the osteoprogenitor cells.29 Absence of necrosis or foreign body reactions indicated that the allogeneic block grafts are biocompatible.
This case series demonstrated that human mineralized allogenic block grafts could be successfully used with the 3D block technique to reconstruct severely atrophic residual ridges. The presence of newly formed bone, with high osteoblastic activity interspersed in areas of lamellar bone, is an indicative of remodeling of the grafted blocks. Therefore, the observation of newly formed vital bone at 8 months after the bone augmentation procedure suggested that the 3D block technique could successfully augment atrophic ridges.
The authors claim to have no financial interest in any company or any of the products mentioned in this article.
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