Histopathological, histomorfometrical, immunohistochemical and tomographical evaluation of the changes in bone by loading of mini-screw

The aim of this study is histopathological, immunohistochemical, histomorphometrical and mikro-tomographical evaluation of the changes observed in the rabbit tibia bone by the application of mini-screws with different geometry and diameter.In this study eighteen adult male rabbits are used. Cylindrical mini-screws of diameter 1.5 mm (designated as A), conical mini-screws of diameter 1.5 mm (B), conical screws of diameters 1.4 mm (C) and 1.6 mm (D) with fine-pitch threads close to screw head, were inserted in rabbit tibia. The mini-screws were inserted to the right tibia bone by recording the applied torque. Ni-Ti coil-springs that are arranged to apply 1 N force were attached between the mini-screws. The rabbits were sacrificed at the end of the 1st, 3rd and 5th weeks. Then the mini-screws were removed by measuring in the torque values and the bone has been evaluated histopathologically, histomorphometrically, immunohistochemically (RANK and OPG) and micro-tomographically.Compared with conical B, C and D mini-screws, cylindrical A mini-screws were delayed bone healing at the end of 1st, 3rd and 5th weeks and removal torque values of A mini-screws were found lower. At the end of the first week RANK immunoreactivity in B mini-screws and OPG immunoreactivity in C mini-screws were observed. At the end of 3rd and 5th weeks an increase in OPG immunoreactivity were recorded in the bone for the cases where B, C, D mini-screws have been applied. Best bone healing and osteoblastic activity were observed in the bone by the use of C and D mini-screws and higher removal torque values were also recorded for these cases. D mini-screws with wider diameter required higher removal torque values than C mini-screws.It is observed that conical with fine-pitch threads close to screw head, were more stable and it is found that stabilization increases with increasing diameter.