Improvement in zirconia osseointegration by means of a biological glass coating: An in vitro and in vivo investigation

The biocompatibility and osseointegration of zirconia (ZrO₂), either coated with RKKP bioglaze® or uncoated, were evaluated in vitro and in vivo. The in vitro test was performed in human osteoblasts, whereas maximal sensitization was performed in 23 Dunkin Hurtley guinea pigs. RKKP bioglaze-coated and uncoated (controls) ZrO₂ cylinders were implanted in the distal femoral epiphyses of 14 Sprague-Dawley rats under general anesthesia, and animals were sacrificed at 30 and 60 days. Lactate dehydrogenase, alkaline phosphatase, and Thiazolyl Blue (MTT) were tested in vitro. A graded score was used for evaluating the results of the sensitization test. Histomorphometry and microhardness testing were performed to quantify the osseointegration rate, as well as bone quality around the implants. Neither in vitro cytotoxicity nor sensitization were observed. Histomorphometry demonstrated that at 30 days, the affinity index was significantly higher in coated implants than in uncoated ones (p <0.05); at 60 days, the behavior of coated implants was better than that of uncoated ones, but differences were not significant. Significant increases in bone microhardness were found at 1000 μm from the interface area for both uncoated (p <0.0005) and RKKP bioglaze®-coated (p <0.0005) ZrO₂, and also within 200 μm from the interface (p = 0.014) but only for coated ZrO₂. These results suggest that RKKP bioglaze®-coated ZrO₂ permits biocompatible devices with improved osseointegration properties to be manufactured.