Primary migration of a mini-implant under a functional orthodontic loading

Abstract

The objective of this study was to examine whether cortical bone thickness and bone mineral density (BMD) can explain the primary migration of a mini-implant under a functional orthodontic tangential loading at the early stage following implantation. Mini-implants were installed in human mandibular sections. A constant tangential load (2 N) was applied to the mini-implant under hydration. Creep, which is a time-dependent viscoelastic displacement in the bone surrounding the mini-implant, was assessed as the change in displacement during 2 h of loading. The total migration was measured as a maximum displacement that combined an initial elastic displacement and creep. After removal of the mini-implant, all specimens were scanned together by cone beam computed tomography. Cortical bone thickness and BMD were measured for the bone voxels surrounding the implant site. BMD had significant correlations with the displacement parameters (p < 0.019), but the cortical bone thickness did not (p > 0.272). Permanent bone deformation adjacent to the implant was observed to be resulting from substantial creep development under the orthodontic functional loading level. BMD controls the primary migration of the mini-implant system in mandibular bone. Viscoelastic creep can develop at a small constant functional loading level, leading to migration of the mini-implant. The current results indicated that mini-implant migration can develop under the small level of functional orthodontic load used in clinic. If the active bone remodeling around the mini-implant accelerates the migration, the risk of causing damage in vital organs next to the mini-implant increases.