Polarization of osteoclasts on dental implant materials is similar to that observed on bone

Polarized osteoclasts form sealing zones, (also called clear zones) detectable as actin rings, and ruffled borders to resorb bone. They secrete protons and catabolic enzymes, including tartrate-resistant acid phosphatase (TRAP), through the ruffled borders. We previously reported that polarized osteoclasts develop areas of TRAP activity (TRAP-marks) when cultured on dentin slices [11]. In this study, we examined how osteoclasts recognize dental implant materials. Osteoclasts obtained from murine co-cultures were cultured on implant materials such as titanium (Ti), alumina, zirconia, and sintered hydroxyapatite (sHA), in addition to dentin. Osteoclasts were also treated with reveromycin A (RM-A), which specifically acts on polarized osteoclasts and induces apoptosis. Polarization of osteoclasts cultured on implant materials was evaluated by measuring actin rings, TRAP-marks, and reveromycin A-induced apoptosis. Osteoclasts formed actin rings on all substrates examined. The formation of actin rings on Ti by osteoclasts was inhibited by the GRGDS peptide, but not by the GRGES peptide, suggesting an integrin-mediated polarization of osteoclasts on Ti. Calcitonin, an inhibitory hormone of osteoclast function, disrupted the actin rings that were preformed on Ti and sHA. Osteoclasts put TRAP-marks on sHA and dentin and formed resorption pits on dentin, but failed to form resorption pits on sHA. RM-A induced apoptosis in osteoclasts cultured on Ti and sHA; this was suppressed by calcitonin. These results demonstrate that osteoclasts are able to polarize on dental implant materials similar to the polarization observed on bone.