Orthodontic tunnel miniscrews with and without TiO2 nanotube arrays as a drug-delivery system: In vivo study.

Orthodontic tunnel miniscrews with and without TiO2 nanotube arrays were fabricated to improve the induction of new bone formation and osseointegration. To inject the drug of recombinant human bone morphogenetic protein, tunnels in a conventional machined miniscrew were machined by a computer-numerical-control lathe. TiO2 nanotube arrays to load the drug were also formed on the surface of the tunnel miniscrew by anodic oxidation. To obtain clean TiO2 nanotube arrays, two-step anodic oxidation was conducted. The diameters of TiO2 nanotube window and TiO2 nanotube were ∼70 nm and ∼110 nm, respectively. Three groups, i.e., a conventional machined miniscrew, a tunnel miniscrew without TiO2 nanotube arrays, and a tunnel miniscrew with TiO2 nanotube arrays, were prepared and inserted in the legs of five New Zealand White rabbits. In a histomorphometric analysis, the bone implant contact ratios of the tunnel miniscrews with the TiO2 nanotube arrays and without the TiO2 nanotube arrays were 5.84% and 5.88%, respectively. These values were higher than the value of 4.30% for the conventional machined miniscrew. The bone surface ratios in the tunnel miniscrew with and without the TiO2 nanotube were also higher than those of the conventional machined miniscrew. The measured values of the tunnel miniscrew with and without the nanotube and the conventional miniscrew were 76.75%, 73.41%, and 44.82%, respectively, although the differences were statistically insignificant. New bone at three weeks and six weeks after the operations were found in the tunnel miniscrews in fluorescent images. Both the tunnel miniscrews with and without the TiO2 nanotube arrays demonstrated greater bone formation compared to the conventional miniscrews. However, TiO2 nanotube arrays was not likely to provide additional benefit to the tunnel miniscrew. An in vivo study suggested that the tunnel fabricated in the miniscrew can be efficient drug-delivery systems to improve osseointegration.