Histological and biomechanical evaluation of phosphorylcholine-coated titanium implants

Objective: Compounds considered for drug delivery from oral implant surfaces in support of local bone formation might themselves influence osseointegration. Phosphorylcholine (PC) polymers have been shown to enhance the biocompatibility of medical devices and to serve as drug delivery systems. The objective of this study was to evaluate local bone formation and osseointegration at PC and positively charged PC (PC+)-coated endosseous implants in an established rabbit model. Material and Methods: Sixteen adult female New Zealand White rabbits were used. Eight animals received PC-coated and control titanium porous oxide surface implants placed in the left and right distal femural condyle (trabecular bone) and proximal tibial metaphysis (cortical bone) using aseptic routines. The remaining eight animals similarly received PC+ and control implants. One implant was placed in each femural condyle and two implants in each tibial metaphysis. Experimental and control implants were alternated between the left and right hind legs. Fascia and skin were closed in layers. The animals were euthanized following a 6-week healing interval for biomechanical (removal torque) and histometric analyses. Results: Peri-implant bone density was considerably greater at tibial compared with femoral sites within as well as immediately outside the implant threads. However, there were no significant differences in bone density among PC, PC+, and control implants. Nevertheless, bone-implant contact was significantly lower at PC compared with PC+ and control implants in cortical bone (p<0.05). Numerical differences in trabecular bone did not reach statistical significance. The removal torque evaluation revealed significantly lower values for PC compared with PC+ and control sites (p<0.05). Conclusion: The histometric and biomechanical analyses suggest that PC coating may influence biological processes and ultimately osseointegration of endosseous implants. Apparently, incorporation of cationic charges may reverse or compensate for this scenario. Nevertheless, both PC coatings exhibited clinically acceptable osseointegration. In perspective, PC technology appears to be a viable candidate delivery system for agents in support of local bone formation at endosseous implant surfaces.