Morphologic, Mechanical, and Molecular Aspects of TGF-Β2 Enhanced Implant Fixation

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Abstract

The fixation of orthopedic and dental implants is dependent upon the ability of newly formed bone to provide a mechanical connection between the implant and host skeleton. There is increasing interest in developing treatments to enhanee the innate reparative capabilities of bone. Uncemented fixation, one of the two primary options which exist to anchor dental and orthopedic implants to bone, initially arose as an alternative to cemented fixation in response to high rates of aseptic loosening experienced during early procedures. Presently, uncemented fixation has demonstrated long-term clinical success, and is particularly suited to revision surgeries where reduced bone stock is available. Provided the necessary conditions exist; initial stability, correct surface characteristics, and an aseptic environment, implant fixation will be achieved. Further it is believed that initial stability and osseous growth are necessary for long term clinical success. The basis for this dissertation was to attempt to augment this innate reparative response. Aim 1 evaluated whether saline irrigation prior to implant placement affected bone formation or implant fixation in a rat model. The experiment revealed that saline irrigation had no effect on either new bone formation adjacent to the implant, bone implant contact, or implant fixation strength. Aim 2 was divided into two studies. The first experiment investigated the effect of exogenously applied recombinant human transforming growth factor beta-2 (rhTGF-p2) on bone formation and implant fixation, and the subsequent study evaluated the temporal expression profile of 21 osteogenic related genes. Consistent with previous studies, local application o f TGF-P2 enhanced bone regeneration and implant fixation. The molecular study suggested that the TGF-P2 enhnaced the innate regenerative response by accelerating, delaying or augmenting transcription profiles of osteogenic genes. Aim 3 focused upon the effect of exogenously applied recombinant human hone morphogenetic protein-2 (rhBMP-2) on bone formation and implant fixation. BMP-2 is a known potent osteoinductive agent, yet the present morphologic and mechanical study failed to reveal its benefit.

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