Comparison of different surface modifications for titanium implants installed into the goat iliac crest

Abstract

Objectives: This in vivo study with implants installed in the goat iliac crest was performed to determine whether the biological and mechanical properties of the bone-to-implant interface are influenced by (i) the type of implant anchorage (i.e., mono- vs. bicortical placement), and (ii) the presence of a bioactive hydroxyapatite (HA) or composite HA/bioactive glass (BG) coatings.

Materials and methods: A total of 96 titanium (Ti) implants w/- coatings (Ti, Ti-HA & Ti-HABG; n = 8) were mono- or bicortically placed in the iliac crest of eight goats. At installation and after 4 weeks, implant stability was determined using insertion and removal torque testing (ITQ & RTQ). The peri-implant bone response was histologically and histomorphometrically evaluated by means of bone-to-implant contact (BIC%) and bone area (BA%).

Results: Monocortical implants demonstrated significantly lower RTQ values in comparison to ITQ values, whereas for bicortical implant placement RTQ and ITQ were similar. Further, mean RTQ values for monocortical implants were significantly lower in comparison to bicortical implants. Histomorphometrical evaluation demonstrated higher BIC% and BA% for bicortical implants compared to monocortical implants. For bicortical implants, BA% in the inner peri-implant region (0-500 μm) was significantly higher compared to the middle (500-1000 μm) and outer (1000-1500 μm) region. Also, a significant correlation was observed for monocortical implants between RTQ and BIC% and BA%. For surface modifications, no significant differences were found in ITQ and RTQ, for neither mono- nor bicortical implants. Histomorphometrically, HABG-coated implants demonstrated significantly higher BIC% compared to GAE surfaces for both mono- and bicortical implants. Bicortical HA-coated implants revealed significant higher BA% in the inner peri-implant region (0-500 μm) in comparison to bicortical GAE implants.

Conclusions: This study demonstrated that bicortical implant placement beneficially affects implant stability during the early phase of osseointegration. A significant correlation between removal torque and bone-to-implant contact and bone area for monocortical implants was observed, but not for bicortical implants. Therefore, histomorphometrical data should be interpreted with caution to predict the biomechanical implant fixation of bone implants over time. Regarding surface modifications, in the present implantation model, the addition of BG to an RF magnetron sputtered HA coating enhanced the biological behavior of the coating compared to grit-blasted/acid-etched implants.