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Hard tissue implant interface.

The osseointegrated interface demonstrates, on an average, some 60-70 per cent bone bordering the implant at the light microscopical level of resolution whereas ultrastructural studies have revealed that only partly calcified proteoglycan layers build up the actual interface. Interfacial bone reactions are dependent on the precise nature of the implant material, its design and surface characteristics supposing that clinical factors such as host reactions and surgical and prosthodontic techniques are being controlled. The most commonly used, although not the only useful, material in oral implantology is cp titanium, a most biocompatible material. The most commonly used oral implant design is the threaded screw whereas cylindrical implants without retention elements have been largely abandoned. The nature of the implant surface is of clear relevance for interfacial reactions; micron-sized irregularities are necessary for osseointegration or biomechanical bonding. Currently, there is evidence of bone ingrowth dependent on nanometer sized irregularities, even if the clinical relevance of this finding remains uncertain. The discussion about an alternative type of implant anchorage (biochemical bonding), started decades ago, however so far without any undisputable evidence of its importance for the oral implant anchorage. Lately, the long-term stability of the oral implant interface has been questioned by some investigators, allegedly it would be threatened by an increasing occurrence of peri-implantitis, however in reality demonstrated for only about 2 per cent of implants over a 10-20 year follow-up.