Bioactive glass particles and deproteinized bovine bone mineral as scaffold in bone tissue regeneration:effects of Minocycline-HCL.

peer reviewedAim/Hypothesis: Bone tissue regeneration remains an important challenge in orthopaedic and maxillofacial surgery. The present study in rat was performed to determine if Minocycline could influence the behavior of Deproteinized Bovine Bone Mineral (DBBM) and bioactive glass particles when used as scaffold for Guided Bone Regeneration (GBR). Minocycline is a wide spectrum antibiotic with demonstrated effects on bone formation, bone resorption and connective tissue breakdown. We chose to investigate this molecule in relation with bioactive glasses and DBBM, both important classes of bone grafting materials. Material and methods: Two completely occlusive titanium bone augmentation caps were placed on each side of the sagittal cranial suture of the rat calvaria. One was filled with bioactive glass particles (BioGran-Biomet 3i, Plam Beach, FL, USA) and the second with DBBM particles (Bio-Oss®–Geistlich, Wolhusen, Switzerland). Bone filler particles were mixed with blood, collected from the animal’s tail, and a drop of balanced salt solution in order to acquire a moldable consistency of the particles and a perfectly adapted fill of the regeneration chambers. In Minocycline-Cl group (n=10) bone grafts were additionally placed into a minocycline solution at 0.1 mg/ml prior placement. The study protocol included animal accommodation with water ad libitum, regular rat pellet with artificial light with a night and day cycle. All surgeries were conducted under strict aseptic conditions. For each observation time (4, 8 and 16 weeks) two calvaria were embedded in methyl methacrylate resin and cut in thin serial sections (100-200 µm), grounded and polished to a thickness of 20-40 µm. A Giemsa (Gross & Strunz, 1977), Paragon and a combination of Stevenel’s blue with Van Gieson staining was used for light microscopy. The remaining calvaria were fixed, decalcified in an EDTA solution at 0.2 M (pH 7.4) for 30 days and dehydrated in ascending ethanol series for 96 h. The paraffin embedded blocks were sectioned (5 µm) and either hematoxylin eosin (H&E) or Toluidine blue stained for the histologic analysis. Results: This study has confirmed osteoconductive and osteoinductive response of BioGran. The addition of Minocycline has hardly influenced the result positively. In contact with blood, BioGran underwent a surface modification in form of a calcium phosphate precipitate, quite similar in composition and structure to hydroxyapatite. Cracks in the outer shell were to be recognized and the silica core tended to disappear leaving a calcium phosphate pouch for future bone growth. Likewise, first signs of osteoinduction in the form of ectopic mineralization foci could be observed after just 4 weeks at some distance from BioGran particles. These ossification islets were lined by a layer of osteoblasts for centrifugal expansion. The osteoconductivity and predictability of Bio-Oss®, are well documented. Some studies however found that Bio-Oss® inhibited new bone formation or interfered with new bone generation especially when used as an onlay graft under totally occlusive capsules in a GTR model. Our observations were similar: the major part of the biomaterial particles was embedded in connective tissue. Most of the new bone regenerated were lamellar bone formations in close contact and bonded to the DBBM particles. Islands of spontaneous ossification suggesting some osteoinductive activities could only be observed in Bio-Oss® sections treated with Minocycline. A possible correlation of these centres with the basal skull bone, outside of our observation field, cannot be excluded. Conclusions and clinical implications: The osteoconductive and osteoinductive properties of bioactive glass particles could be confirmed within the limitations of the present study. Minocycline-HCl may be considered as a promising complementary treatment approach and may add some osteoinductive properties to DBBM. Further investigations into the volume of the newly generated bone are needed to refine the present results