Mechanical Evaluation of Mandibular Defects Restored with rhBMP-2: A Finite Element Model
Introduction: The utilization of recombinant human Bone Morphogenetic Protein-2 (rh- BMP2) to form new bone has been shown to be a promising alternative to autogenous bone grafts. Understanding the biomechanical properties of rhBMP-2 restored mandibular defects would provide useful knowledge in the future success of orthopedic and dental treatment in patients who have had restoration of mandibular defects with rhBMP-2. The aim of the study was to evaluate and compare the biomechanical characteristics of rhBMP-2 regenerated bone in mandibular defects using 2 different concentrations of rhBMP-2 with a given carrier in non-human primates Material and Methods: Critical-sized defects (approximately 2.5 cm) were created in the mandibles of 6 adult male non-human primates. Each side of the mandibles received one of 2 carrier types: 1) 1.35 mg/mL rhBMP-2 combined with a collagen ceramic sponge (CCS) and 2) 0.75 mg/mL rhBMP-2 combined with CCS. All defects were stabilized with a titanium reconstruction plate. Young's modulus of 10 bone samples was calculated using the results from a tensile test of the samples. Density of the 10 samples was determined with a pycnometer. A 2-dimensional model of the mandible was virtually created to simulate the mandible for a given BMP/carrier group. Subdomains of the model included cortical bone, regenerated bone, periodontal ligament, enamel, and cementum. Boundary conditions of the subdomains were assigned using the biomechanical properties determined in the literature and the regenerated bone values were assigned based on prior testing. Finite Element Analysis was performed with the COMSOL Finite Element Modeling software to measure peak Von Mises stresses and surface displacement of the newly regenerated bone in response to a 150 N force of the masseter muscle. Results: There was no statistical difference between the mechanical properties among treatment groups. However, both treatment groups showed a statistically significant difference in stress distribution, displacement in the x-axis, and displacement in the yaxis when compared to the control group (p < 0.05) but no statistically significant difference when compared to each other (p < 0.05). Conclusions: The differences in stress distribution and displacement when comparing the treatment group to the control group indicate that the treatment group regenerated bone was less stiff which lead to more displacement in the mandible and higher stress in response to function. This may be attributed to the 6-month follow-up period where the regenerated bone did not complete mineralization. The similarity in mechanical properties, stress, and displacement between treatment groups indicate that a rhBMP-2 concentration of 0.75 mg/mL produced bone that was biomechanically comparable to a concentration of 1.35 mg/mL.
Orthodontics and Orthodontology, Other Dentistry, Bone Morphogenetic Proteins; Bone Development; Growth Substances; Recombinant Proteins; Bone Morphogenetic Protein 2; Bone regeneration; Mandible - surgery, Mandibular defects, Recombinant human bone morphogenetic protein-2, bone growth
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