Effect of immediate loading on the biomechanical properties of bone surrounding the miniscrew implants

The aim of this study was to investigate the effect of immediate loading on the biomechanical properties of bone surrounding a miniscrew implant. Forty titanium alloy miniscrew implants were placed on the buccal side of the maxillae and mandibles in four beagle dogs. Twelve pairs of miniscrew implants were immediately loaded with approximately 150 g of continuous force using nickel-titanium coil springs and the remaining 16 implants were left unloaded for 8 weeks. Nanoindentation testing was performed (peak load 10 mN) and the hardness and elastic modulus were calculated. Two series of indentations (in cortical and trabecular bone) for both the compression and tension sides were made. For each site, five indentations were placed approximately 25 μm from the implant-bone interface and 250 μm from the screw thread. The mean hardness and elastic modulus were generally higher in mandibles than maxillae and were higher in cortical bone than in trabecular bone. The trabecular bone near the implant-bone interface on the compression side was significantly harder than that at other locations in trabecular bone. In conclusion, this is the first study that has investigated the biomechanical properties of bone surrounding a miniscrew implant under immediate loading using nanoindentation testing. The mechanical properties of bone surrounding a miniscrew implant may be influenced by immediate loading.