Ultrastructural characterization of the implant interface response to loading

Dynamic loading can affect the bone surrounding implants. For ultrastructural exploration of the peri-implant tissue response to dynamic loading, titanium implants were installed in rat tibiae, in which one implant was loaded while the contralateral served as the unloaded control. The loaded implants received stimulation either within 24 hrs after implantation (immediate loading) or after a 28-day healing period (delayed loading) for 4, 7, 14, 21, or 28 days. The samples were processed for histology and gene expression quantification. Compared with the unloaded control, bone-to-implant contact increased significantly by immediate loading for 28 days (p < .05), but not in case of delayed loading. No effect of loading was observed on the bone formation in the implant thread areas, on the blood vessel area, and on endosteal callus formation. Loading during healing (immediate) for 7 days induced, relative to the unloaded control, a 2.3-fold increase of Runx2 in peri-implant cortical bone (p < .01) without a change in the RANKL/Opg ratio. Loading after healing (delayed) for 7 days up-regulated Runx2 (4.3-fold, p < .01) as well as Opg (22.3-fold, p < .05) compared with the unloaded control, resulting in a significantly decreased RANKL/Opg ratio. These results indicate a stimulating effect of dynamic loading on implant osseointegration when applied during the healing phase. In addition, gene expression analyses revealed molecular adaptations favoring bone formation and, at the same time, affecting bone remodeling.