Evaluation of New Bone Formation and Osseointegration Around Subperiosteal Titanium Implants with Histometry and Nanoindentation

Purpose: To assess the quality and quantity of newly formed bone around rough-surfaced titanium subperiosteal implants stabilized with two different fixation techniques and to investigate nanoindentation as a method for measuring the elastic properties of the bone around these implants. Materials and Methods: Ten 6-month-old white rabbits were used in this study. One femur received a subperiosteal implant fixed to the bone with screws. The other femur received a subperiosteal implant stabilized with a trough (bed) in the bone area, plus fixation screws. After a 3-month healing period, the animals were sacrificed and each titanium plate was resected along with the surrounding bone. Histometric measurements of osseointegration were performed on 16 titanium plates, and 16 titanium plates were evaluated qualitatively (hardness and modulus of elasticity) with nanoindentation. A regression model was used to analyze the data. Results: Subperiosteal implants placed into a trough performed significantly better than those placed on top of the cortical bone in terms of percentage of bone in direct contact with the titanium plate, length of new bone, and percentage of area of new bone. The mechanical properties (modulus of elasticity, hardness) of the newly formed bone above the plate measured at the microstructural level were significantly inferior to those of the mature cortical bone below the plate. Conclusion: Subperiosteal implants placed into a trough performed better than those placed on top of the cortical bone, but it seems that 3 months of healing is not enough to achieve optimal integration and bone maturation around them. Nanoindentation can offer valuable insight into the elastic properties of the microstructural component of the bone. Keywords: nanoindentation, subperiosteal, titanium implant