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This issue of rewind looks into a new bone regenerative material i.e. bioglass. Dr. A. Kumarswamy discusses this new material and its significance in relation with other contemporary bone regenrative materials used in the past. BIOGRAN - An Osseoinductive Bioceramic Material Biogran is a biocompatible material developed almost a decade ago. The earliest researchers to report on Biogran were E.Schepers, P. Ducheyne and Hench LL. Biogran today is a product manufactured & sold by Orthovita, with indications to be used for repair of bony periodontal defects around natural teeth, ridge augmentation, bony defects around teeth, in cystic lesions and in almost any kind of intraoral osseous defect requiring bone regeneration. Biogran is an alloplastic material composed of 45 % SiO2 , 24.5 % CaO, 24.5 % Na2O and 6% P2 O5 by weight. It is made of bioactive glass 45S5. The material is essentially irregularly shaped granules processed to a uniform particulate size of 300-355 microns. It is a re sorbable material with multiple bone related properties attributed to it. It has been called osteoconductive, osteostimulative, bioactive. Biogran directly bonds to the bone and has an amorphous structure due to which it is not classified as a ceramic but rather as glass. The material has a distinctive bone formation mechanism, which can be attributed towards the quite successful clinical results achieved when using this material. The Golden Standard as of today is essentially autogenous bone for the repair of osseous defects. Commonly used alloplastic materials have been hydroxyapatite and tricalcium phosphate. However both these materials have suffered in comparison to autogenous bone in the ability to repair intraoral ossesous defects. Even though bo th these materials are bioactive since they form a direct bond with the bone, the material handling characteristics and other clinical parameters like connective tissue and epithelial infiltration have greatly diminished their promise and thereby actual c linical efficacy. Mode of Action : As mentioned earlier Biogran is a bioactive material and forms a chemical bond with the bone. Hence retention of the material in the defect is facilitated. A chemical reaction in the form of ion exchange takes place betw een Biogran and the body tissues leading to the formation of a Si rich layer covered with a CaP rich layer. The SiO2 in the glass is transformed into a loose silica gel by a dissolution process when reacting with body fluids. It is most likely that Biogra n also bonds to the soft tissue which prevents its migration when encapsulated by fibrous tissue. It is postulated that the granules tend to develop microcracks due to the shrinkage associated with the formation of this layer. Phagocytes penetrate these microcracks and initiate the excavation and resorption of the inner silica gel core. Lab research has shown that osteoprogenitor cells penetrate these microcracks and differentiate into osteoblasts, thus promoting new bone formation. Histology sections of sites grafted with Biogran show bone formation in the core of the granules. This leads to an inside out growth of bone within the Biogran granules. At the same time osteoconductive bone growth is seen on the periphery of the granules. This leads to a dual mode of bone formation. A unique finding to be stressed is that particles which are in close proximity to existing bone exhibit greater bone formation on the periphery while particles which further away from pre-existing bone show greater bone formation in the core. It is also important to note that the bone being formed in the central core is not connected initially to the bone forming on the periphery of the particles. This shows that the internal excavation and bone formation continues as an independa nt entity. The CaP rich layer is similar in characteristic to the mineral phase of bone formation and this leads to the laying down of osteoid tissue. Bony trabaculae form along the periphery ultimately leading to and connecting with the bone forming in t he cores of the particles. By 6 months most of the particles tend to be totally engulfed by the new forming bone and by about 12 months the particles are almost totally replaced by new formed bone tissue. Clinical Significance: The excellent material hand ling characteristics of this material makes Biogran a very easy material to manipulate in the oral cavity. The granules on contact with blood tend to aggregrate and stick to each other which prevents washing away of the graft material with saliva and blood. Biogran also tends to provide a semblance of a clotting mechanism which again aids in preventing the washing away of the granules. \par \par There is some early evidence of Biogran inhibiting or delaying epithelial downgrowth which is a very important factor in its ability to repair periodontal defects. In case of large defects a resorbable membrane can be placed over the filled defect to prevent connective tissue infiltration and also to stabilize the defect area. Conclusion: Biogran holds excellent promise as not only a substitute but a replacement for the Golden Standards of autogenous bone in its ability to repair a variety of osseous defects in the oral cavity. When used in conjunction with good resorbable membranes it can very nearly give predictable results which were just not possible a decade ago.
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