The effects of micromachined surfaces on formation of bonelike tissue on subcutaneous implants as assessed by radiography and computer image processing.

Surface topography varies widely among commercially available orthopedic and dental implants. While it is generally accepted that the surface topography of an implant influences the formation of bone and affects its performance, few systematic studies have dealt with this important feature. Quantification of the mineralized tissue at the implant interface has typically been attempted using histologic methods or conventional radiographic procedures. However, histologic methods are often technically demanding and time consuming, whereas conventional radiographic procedures lack resolution and sensitivity to identify small areas of mineralization. The objective of this study was to study systematically the effects of micromachined surfaces on bone formation by applying digital radiographic techniques to identify and quantify mineralized tissue. Titanium-coated epoxy replicas of 19 different micromachined grooved or pitted surfaces that ranged between 30 and 120 microns deep, as well as smooth control surfaces, were implanted percutaneously and fixed to the parietal bone of rats. After 8 weeks the implants and attached tissue were removed and processed for light and electron microscopy. A total of 316 implant surfaces were processed, radiographed using conventional and digital techniques, and sectioned for histologic observations. The area of the bonelike tissue and its density were calculated using National Institutes of Health Image software. Mineralization was frequently noted at the interface of some types of micromachined surface but rarely on smooth surfaces. The presence of bone in histologic sections and areas identified as bone through digital radiography and image processing correlated strongly. The frequency of bonelike foci formation decreased as the depth of the grooves increased. In contrast, mineralization occurred more frequently as the depth of the pit increased. In addition, bonelike foci were oriented along the long axis of the grooves. It is thus feasible that the bonelike tissue is shaped, directed, or engineered to a predetermined configuration which is dictated by the surface topography. This study indicated that surface topography influences the frequency as well as the amount of bone deposited adjacent to implants, and mineralized product can be guided by the surface topography. Moreover, digital radiography and image processing can be used reliably to identify and quantify mineralized tissue at the implant interface.