The basic science of bone induction

Custom-made computer-aided-design/ computer-assisted-manufacturing (CAD/CAM) synthetic bone grafts for alveolar ridge augmentation: A retrospective clinical study with 3 years of follow-up

PURPOSE

To report on the results obtained with computer-aided-design/ computer-assisted-manufacturing (CAD/CAM) custom-made synthetic hydroxyapatite/beta-tricalcium-phosphate (HA/beta-TCP) bone grafts in alveolar ridge augmentation for dental implant placement.

METHODS

The procedure included: (1) cone-beam computed tomography (CBCT) of the bone defect; (2) virtual design of the custom-made onlay bone grafts; (3) milling of grafts from a pre-formed block of synthetic HA/beta-TCP; and (4) bone reconstructive surgery. Implants were placed 8 months later. The patients were followed for 3 years. The study outcomes were: (1) intra- and immediate post-operative complications; (2) 8-month vertical and horizontal bone gain; (3) implant survival; (4) implant-crown success; and (5) peri-implant marginal bone loss (MBL).

RESULTS

Twenty-six patients underwent ridge augmentation with custom-made CAD/CAM HA/beta-TCP onlay grafts. Eight months later, these patients were rehabilitated with dental implants. During surgery, 25/26 (96.1%) of the grafts adapted well to the bone defect. Immediate post-operative complications were pain and swelling (2/26 patients: 7.6%), and bone graft exposure (3/26: 11.5%); one exposure led to infection, removal of the graft, and failure of the procedure. Excellent integration of the other grafts was observed 8 months after the regenerative procedure, with mean vertical and horizontal bone gains of 2.10 mm (± 0.35) and 2.96 mm (± 0.45), respectively. Twenty-five implants were placed and restored with single crowns. Three years later, all implants were in function. The 3-year implant crown success rate and peri-implant MBL were 92.0% and 0.7 mm (±0.19), respectively.

CONCLUSIONS

With custom-made CAD/CAM synthetic HA/beta-TCP onlay grafts reconstruction of small vertical and/or horizontal defects of the alveolar ridge was obtained; this enabled implant placement, with high implant-crown success rate after 3 years. Further studies are needed to validate this technique.

STATEMENT OF CLINICAL RELEVANCE

Custom-made CAD/CAM synthetic HA/beta-TCP onlay grafts may represent an option for regeneration of small bone defects prior to implant placement.

Bone tissue engineering in the greater omentum is enhanced by a periosteal transplant in a miniature pig model

Aim: Reconstruction of bone defects with autologous grafts has certain disadvantages. The aim of this study is to introduce a new type of living bioreactor for engineering of bone flaps and to evaluate the effect of different barrier membranes. Materials & methods: Scaffolds loaded with bone morphogenetic proteins and bone marrow aspirate wrapped with either a collagen membrane or a periosteal flap were implanted in the greater omentum of miniature pigs. Results: Both histological and radiographic evaluation showed proven bone formation and increased density after 8 and 16 weeks, with an enhanced effect of the periosteal transplant. Conclusion: The greater omentum is a suitable bioreactor for bone tissue engineering. Endocultivation is both an innovative and promising approach in regenerative medicine.

Engineering microdent structures of bone implant surfaces to enhance osteogenic activity in MSCs

Problems persist with the integration of hip and dental implants with host bone tissues, which may result in long-term implant failure. Previous studies have found that implants bearing irregular surfaces can facilitate osseointegration. An improvement to this approach would use implant surfaces harboring a well-defined surface microstructure to decrease variability in implant surfaces. In this study, we tested whether well-defined surfaces with arrays of microdents (each with depth approximately 3 µm) significantly affected the morphology, proliferation, and osteogenic activity of mesenchymal stem cells (MSCs). Arrays of microdents tested had diameters of 9 µm, 12 µm, and 18 µm, while spacing between arrays ranged from 8 µm to 34 µm. Effects on MSC morphology (cell spreading area) and proliferation were also quantified, with both significantly decreasing on micropatterned surfaces (p<0.05) on smaller and denser microdents. In contrast, MSCs were found to deposit more calcified matrix on smaller and denser arrays of microdents. MSCs on a pattern with arrays of microdents with a diameter of 9 µm and a spacing 8 µm deposited 3-4 times more calcified matrix than on a smooth surface (p<0.05). These findings show that well-defined surface microtopographies promote osteogenic activity, which can be used on implant surfaces to improve integration with the host bone tissue.

Custom-Made Synthetic Scaffolds for Bone Reconstruction: A Retrospective, Multicenter Clinical Study on 15 Patients

Purpose. To present a computer-assisted-design/computer-assisted-manufacturing (CAD/CAM) technique for the design, fabrication, and clinical application of custom-made synthetic scaffolds, for alveolar ridge augmentation. Methods. The CAD/CAM procedure consisted of (1) virtual planning/design of the custom-made scaffold; (2) milling of the scaffold into the exact size/shape from a preformed synthetic bone block; (3) reconstructive surgery. The main clinical/radiographic outcomes were vertical/horizontal bone gain, any biological complication, and implant survival. Results. Fifteen patients were selected who had been treated with a custom-made synthetic scaffold for ridge augmentation. The scaffolds closely matched the shape of the defects: this reduced the operation time and contributed to good healing. A few patients experienced biological complications, such as pain/swelling (2/15: 13.3%) and exposure of the scaffold (3/15: 20.0%); one of these had infection and complete graft loss. In all other patients, 8 months after reconstruction, a well-integrated newly formed bone was clinically available, and the radiographic evaluation revealed a mean vertical and horizontal bone gain of 2.1 ± 0.9 mm and 3.0 ± 1.0 mm, respectively. Fourteen implants were placed and restored with single crowns. The implant survival rate was 100%. Conclusions. Although positive outcomes have been found with custom-made synthetic scaffolds in alveolar ridge augmentation, further studies are needed to validate this technique.

Blood vessels are concentrated within the implant surface concavities: a histologic study in rabbit tibia

Angiogenesis plays a key role in bone formation and maintenance. Bone formation has been reported to initiate in the concavities rather than the convexities in a hydroxyapatite substratum and the implant threads of dental implants. The aim of the present study was to evaluate the number of the blood vessels inside the concavities and around the convexities of the threads of implants in a rabbit tibia model. A total of 32 thread-shaped implants blasted with apatitic calcium phosphate (TCP/HA blend) (Resorbable Blast Texturing, RBT) (Maestro, BioHorizons(®), Birmingham, AL, USA) were inserted in 8 rabbits. Each rabbit received 4 implants, 2 in the right and 2 in left tibia. Implants were retrieved after 1, 2, 4, and 8 weeks and treated to obtain thin ground sections. Statistically significant differences were found in the number of vessels that had formed in the concavities rather than the convexities of the implants after 1 (p = 0.000), and 2 weeks (p = 0.000), whilst no significant differences after 4 (p = 0.546) and 8 weeks (p = 0.275) were detected. The present results supported the hypothesis that blood vessel formation was stimulated by the presence of the concavities, which may provide a suitable environment in which mechanical forces, concentrations and gradients of chemotactic molecules and blood clot retention may all drive vascular and bone cell migration.

Local delivery of small and large biomolecules in craniomaxillofacial bone

Current state of the art reconstruction of bony defects in the craniomaxillofacial (CMF) area involves transplantation of autogenous or allogenous bone grafts. However, the inherent drawbacks of this approach strongly urge clinicians and researchers to explore alternative treatment options. Currently, a wide interest exists in local delivery of biomolecules from synthetic biomaterials for CMF bone regeneration, in which small biomolecules are rapidly emerging in recent years as an interesting adjunct for upgrading the clinical treatment of CMF bone regeneration under compromised healing conditions. This review highlights recent advances in the local delivery small and large biomolecules for the clinical treatment of CMF bone defects. Further, it provides a perspective on the efficacy of biomolecule delivery in CMF bone regeneration by reviewing presently available reports of pre-clinical studies using various animal models.

What are we reading? A study of downloaded and cited articles from the British Journal of Oral and Maxillofacial Surgery in 2010

A large number of papers related to oral and maxillofacial surgery are published in many specialist journals. With the ever-increasing use of the internet it is easy to download them as part of a journal subscription on a fee per paper basis, or in some cases for free. Online access to the British Journal of Oral and Maxillofacial Surgery (BJOMS) is free to British Association (BAOMS) members with a $30 fee per paper download for non-members. Many colleagues use the online version of the journal, and this provides valuable information about downloading trends. Other data on articles that have been cited in subsequent publications are also readily available, and they form the basis for the calculation of a journal's impact factor. We evaluated the top 50 downloaded papers from the BJOMS website in 2010 to ascertain which articles were being read online. We also obtained data on the number of citations for papers published in 2009-2010 to see whether these papers were similar to the articles being downloaded. In 2010 there were over 360000 downloaded articles. The most popular papers were leading articles, reviews, and full length articles; only one short communication featured in the top 50 downloads. The papers most cited in subsequent publications were full length articles and leading articles or reviews, which represent 80% of the total citations of the 50 papers. Ten papers were in both the top 50 downloaded and most cited lists. We discuss the implications of this study for the journal and our readers.

Recombinant human bone morphogenetic protein 2 combined with an osteoconductive bulking agent for mandibular continuity defects in nonhuman primates

PURPOSE

Recombinant human bone morphogenetic protein 2 (rhBMP-2) is an option for reconstructing mandibular continuity defects. A challenge of this technique is the need to maintain sufficient space to avoid compression of the defect. A compression-resistant matrix (CRM) provides a bulking agent that provides support during the bone formation phase.

MATERIALS AND METHODS

Thirteen Rhesus Macaque monkeys were used to evaluate different forms of an osteoconductive bulking agent compared with an absorbable collagen alone placed into a critical-sized mandibular defect. A total of 5 groups (26 defects) were evaluated: group A, rhBMP-2/absorbable collagen sponge (ACS) (1.5 mg/mL); group B, rhBMP-2/ACS with ceramic granules (15% hydroxyapatite/85% β-tricalcium phosphate) at 1.5 mg/mL; group C, rhBMP-2 (2.0 mg/mL) with a CRM; group D, rhBMP-2 (0.75 mg/mL) with a CRM; and group E, a CRM alone.

RESULTS

Histology and micro computed tomography were used to evaluate and compare new bone formation in the defects. The reconstructed bone was evaluated with regard to the new bone formation, residual voids, and density. Animals treated with the CRM and rhBMP-2 at 2.0 mg/mL (group C) showed significantly higher amounts of new bone formation, bone density, and reduced voids when compared with rhBMP-2 and ACS (1.5 mg/mL) (P < .05).

CONCLUSION

The carrier system CRM combined with rhBMP-2 and a reconstruction plate results in significantly higher bone density and better space maintenance than rhBMP-2 combined with ACS in a nonhuman primate mandibular bone repair model.

The use of platelet rich plasma, bone morphogenetic protein-2 and different scaffolds in oral and maxillofacial surgery - literature review in comparison with own clinical experience

Objectives

The purpose of this article was to review and critically assess the use of platelet rich plasma, recombinant human bone morphogenetic protein-2 and different scaffolds (i.e. tricalciumphosphate, polycaprolactone, demineralized bone matrix and anorganic bovine bone mineral) in oral and maxillofacial surgery comparing the relevant literature and own clinical experience.

Material and Methods

A literature review was conducted using MEDLINE, MEDPILOT and COCHRANE DATABASE OF SYSTEMATIC REVIEWS. It concentrated on manuscripts and overviews published in the last five years (2006-2010). The key terms employed were platelet rich plasma, bone morphogenetic proteins and their combinations with the above mentioned scaffolds. The results of clinical studies and animal trials were especially emphasized. The statements from the literature were compared with authors’ own clinical data.

Results

New publications and overviews demonstrate the advantages of platelet rich plasma in bone regeneration. The results from the literature review were discussed and compared with the publications detailing authors' own experiences.

Conclusions

A favourable outcome concerning newly grown bone was achieved combining platelet rich plasma in addition to optimal matrices with or without recombinant human bone morphogenetic protein-2, depending on the clinical case. As a consequence, the paradigm shift from transplantation of autogenous bone to bone tissue engineering appears promising.

Probing the osteoinductive effect of calcium phosphate by using an in vitro biomimetic model

The use of calcium phosphate (CaP)-based carriers in bone engineering is a promising approach to induce in vivo bone formation. However, the exact mechanism of osteoinduction by CaP is not known. Here, by mimicking the in vivo Ca(2+) and P(i)-enriched environment in an in vitro model, we assessed the effects of these ions on human periosteum-derived cells. We observed a significant Ca(2+) and P(i)-induced cell proliferation, which was found to be through the modulation of cell cycle progression, in a dose- and time-dependent manner. In addition, Ca(2+), P(i), and combined Ca-P upregulated osteogenic gene expression in a dose- and time-dependent manner. Encouragingly, both ions administered individually or in combination persistently and dose dependently upregulated bone morphogenetic protein-2 gene expression. This suggested a potential osteoinductive effect through an autonomous activation of the bone morphogenetic protein signaling pathway by released Ca(2+) and P(i), which may serve as an autocrine/paracrine osteoinduction loop that drives the cellularized CaP constructs toward effective bone formation in vivo. In conclusion, through an in vitro biomimetic model, we have partially probed the roles of the released Ca(2+) and P(i) on the osteoinductivity of CaP-based biomaterials.

Bone-invasive oral squamous cell carcinoma in cats: pathology and expression of parathyroid hormone-related protein

Feline oral squamous cell carcinoma (OSCC) is the most common oral tumor in cats. There is no effective treatment, and the average duration of survival after diagnosis is only 2 months. Feline OSCC is frequently associated with osteolysis; however, the mechanisms responsible are unknown. The objective of this study was to characterize the epidemiology and pathology of bone-invasive OSCC in cats and to determine the expression of select bone resorption agonists. In sum, 451 cases of feline OSCC were evaluated. There was no sex or breed predisposition, although there were more intact cats in the OSCC group compared to the control group. Gingiva was the most common site, followed by the sublingual region and tongue. Cats with lingual OSCC were younger (mean, 11.9 years) compared to cats with gingival OSCC (mean, 13.6 years). In addition to osteolysis, there was periosteal new bone formation, osseous metaplasia of tumor stroma, and direct apposition of OSCC to fragments of bone, suggestive of bone-binding behavior. Eighty-two cases were selected for immunohistochemical detection of parathyroid hormone-related protein (PTHrP). Specimens with osteolysis had increased PTHrP expression and nuclear localization, compared to OSCC without osteolysis. Thirty-eight biopsies of OSCC with osteolysis were evaluated for tumor necrosis factor α expression, and only 4 biopsies had such expression in a small proportion of tumor cells. Increased tumor expression of PTHrP and increased localization of PTHrP to the nucleus were associated with osteolysis and may play an important role in bone resorption and tumor invasion in cats with OSCC.

Osteoinduction: translating preclinical promise into clinical reality

This review, the second in a series of three editorials, focuses on the problems of translating basic scientific research on induction of bone into reliable clinical applications.

Modern bone regeneration instead of bone transplantation: a combination of recombinant human bone morphogenetic protein-2 and platelet-rich plasma for the vertical augmentation of the maxillary bone-a single case report

This publication describes the clinical case of a 75-year-old woman. She suffered from total alveolar ridge atrophy due to 20 years of wearing dentures. Bone transplantation, including harvesting of the iliac crest, was rejected by another clinic due to various existing diseases and risk of blood loss on donor side. Moreover, the minimal residual alveolar ridge did not allow bone fixation using screws nor did it allow osteodistraction. Before deciding which bone tissue engineering techniques should best be employed in this surgical treatment, cardiological and internistic consultations and treatments were carried out. In addition, anesthetic preparations were made. The surgical treatment was performed implementing special bridge flap techniques to preserve the periosteum. Tricalcium phosphate blocks soaked with recombinant human bone morphogenetic protein-2 and platelet-rich plasma were implanted on the narrow alveolar ridge. They were attached by tightening the soft tissue, including the periosteum. Four months later, after complication-free wound healing and bone regeneration, six dental implants were inserted into the new alveolar ridge. The histology of all bone samples showed vital lamellar bone. Three months after implantation, a new dental structure was fixed on the implants. The patient's quality of life improved significantly with this new situation.