Microscopic Imaging and Chemical Analysis of Separated Implant-Bone Surfaces

Objective: This study focuses on analyzing the microscopic structure and chemical properties of bone-implant interfaces of samples obtained from hydroxyapatite coated mandibular cobalt alloy custom implants after roughly eleven years in function.  The hypothesis was that the plasma sprayed coating, which was present at implant delivery, would be mostly resorbed leaving bone integrated directly to the metallic implant surface.

Method: Four bone-implant samples were selected from three post mortem specimens from a previous study (Roberson et al, AADR, 2011) which had sectioned the bone integrated implant structure into roughly 4mm² pieces.  These pieces had been microtensile tested, thus exposing the previously joined bone and implant surfaces.  These pieces were processed to remove possible contaminants and arranged with fractured faces exposed, so they could be viewed initially using a Keyence optical microscope where images showed the microscopic topographical structure. Scanning Electron Microscopy (SEM) provided higher resolution of the implant microstructure and Energy Dispersive Spectroscopy (EDS) spectra provided surface chemical analyses.

Result: Both Keyence and SEM images revealed boney microstructure that mirrored the implant’s roughened surface.  The EDS spectrum of the implant alloy surfaces showed the presence of cobalt, chromium, and molybdenum along with calcium and phosphorous along bone sites.  The boney surface EDS showed calcium and phosphorous, plus carbon and oxygen. Overall, the spectral analyses supported a complex chromium oxide surface on the alloy at the osseous interface region.

Conclusion: We were unable to determine if the hydroxyapatite coating was totally resorbed; however, the bone had grown into the microscopic irregularities of the implant surface, providing the first report of bone integration along dental implant cobalt alloy surfaces after 11 years of human in vivo function.  Future studies are planned to further analyze the chemical structure of these surfaces through ion milling, selected area diffraction, and related EM procedures.