The role of implant surface characteristics in the healing of bone.

The surface of an implant determines its ultimate ability to integrate into the surrounding tissue. The composite effect of surface energy, composition, roughness, and topography plays a major role during the initial phases of the biological response to the implant, such as protein adsorption and cellular adherence, as well as during the later and more chronic phases of the response. For bone, the successful incorporation (and hence rigid fixation) of an alloplastic material within the surrounding bony bed is called osteointegration. The exact surface characteristics necessary for optimal osteointegration, however, remain to be elucidated. This review will focus on how surface characteristics, such as composition and roughness, affect cellular response to an implant material. Data from two different culture systems suggest that these characteristics play a significant role in the recruitment and maturation of cells along relevant differentiation pathways. In the case of osteointegration, if the implant surface is inappropriate or less than optimal, cells will be unable to produce the appropriate complement of autocrine and paracrine factors required for adequate stimulation of osteogenesis at the implant site. In contrast, if the surface is appropriate, cells at the implant surface will stimulate interactions between cells at the surface and those in distal tissues. This, in turn, will initiate a timely sequence of events which include cell proliferation, differentiation, matrix synthesis, and local factor production, thereby resulting in the successful incorporation of the implant into the surrounding bony tissue.