Bone Matrix Protein Expression around Titanium Orthodontic Mini-implant

Objectives: Mini-implants for orthodontic anchorage have become a widely accepted standard in orthodontics; an increasing number of practitioners are using it. Its clinical effectiveness is well documented. But its biological adaptation has not been thoroughly investigated yet. This research was designed to investigate changes of growth factors and bone matrix proteins during the bone healing processes around the orthodontic titanium mini-implant using histomorphometry, immunohistochemistry and confocal laser scanning microscopy. Methods: Threaded titanium mini-implants were introduced into the rat tibia. Animals were sacrificed in 1, 2, 3, 4, 6, 8, 12, 16 weeks after implant placement. Specimens were embedded in resin and undecalcified sections were prepared. Time dependent changes of several bone associated protein were observed using immunofluorescent labeling and confocal laser scanning microscopy. The results were compared with bone histomorphometry. Proteins investigated in this study were collagen, osteonectin(ON), osteocalcin(OC). Bone morphogenetic protein (BMP) and vascular endothelial growth factor (VEGF) expressions were also observed. Results: Bone regenerations were observed as early as the first week of experiment. Bone density were increased rapidly and reached its maximum at 3rd week. At 4th week, extensive remodeling was observed. After 8th week, bone density was not changed significantly. The cellular expression of the collagen, ON and OC were observed mainly in the osteoblast-like cell on the surface of new bone around the implant and the cells lining the margin of bone defect apart from the implant. BMP expressions were observed at 1,2,3 week in lining cells of implant and adjacent bone. VEGF expressions were also observed in the same cells and endothelial cells. Conclusions: Mini-implants showed faster bone healing process compared to larger implants or bone defects. Bone healing processes and expressions of matrix proteins and growth factors were normal.