Can implants move in bone? A longitudinal in vivo micro‐CT analysis of implants under constant forces in rat vertebrae

Abstract

Objectives Whereas stationary stability of implants has been postulated for decades, recent studies suggested a phenomenon termed implant migration. This describes a change in position of implants as a reaction to applied forces. The present study aims at employing image registration of in vivo micro‐CT scans from different time points and to assess (a) if migration of continuously loaded implants is possible and (b) migration correlates with the force magnitude. Material and methods Two customized machined implants were placed in the dorsal portion of caudal vertebrae in n = 61 rats and exposed to standardized forces (0.5 N, 1.0 N, and 1.5 N) applied through a flat nickel–titanium contraction spring, or no forces (control). Micro‐CT scans were performed at 0, 1, 2, 4, 6, and 8 weeks after surgery. The baseline image was registered with the forthcoming scans. Implant migration was measured as the Euclidean distance between implant tips. Bone remodeling was assessed between the baseline and the forthcoming scans. Results The findings confirmed a positional change of the implants at 2 and 8 weeks of healing, and a linear association between applied force and velocity of movement (anterior implant: χ2 = 12.12, df = 3, and p = .007 and posterior implant: χ2 = 20.35, df = 3, and p < .001). Bone apposition was observed around the implants and accompanied by formation of load‐bearing trabeculae and a general cortical thickening close and also distant to the implants. Conclusion The present analysis confirmed that implants can migrate in bone. The applied forces seemed to stimulate bone thickening, which could explain why implants migrate without affecting stability.

Bone remodelling patterns around orthodontic mini-implants migrating in bone: an experimental study in rat vertebrae

“…Registration of volumetric images from the same animal taken at different time points allows investigating the movement patterns of the implants and the related changes in bone micro-structure. Recently, the authors performed a longitudinal in vivo micro-CT study in the rat-tail model and loaded two customized mini-implants per animal by means of flat nickel–titanium spring applying constant forces of 0.0 (control), 0.5, 1.0, and 1.5 N for either 2 or 8 weeks ( 6 ). A significant association between implant tip displacement and loading magnitude, as well as significant decrease in migration velocity over time, was observed.…”

“…Limitations of the present study are related to the limited number of animals available for the respective evaluations. This was due to the fact that the sample size calculation was based on the in vivo micro-CT analysis, which had been previously published ( 6 ). The aim of the present study was to utilize samples from the previous non-destructive method to enable further investigation of the underlying bone remodelling process at molecular and cell levels.…”

“…The protocol has been described in detail previously ( 6 ) and was approved by the appropriate local authority (Landesamt für Natur und Verbraucherschutz), Ref. no.…”

“…Recently, a preclinical study in the rat-tail model employing high-resolution in vivo micro-computed tomography (micro-CT) revealed an association between applied force magnitude and implant displacement. Additionally, the implant migration velocity within the bone decreased over time ( 6 ). Therefore, it is likely that implant migration is accompanied by bone remodelling, which, however, has not yet been verified.…”

“…Previously, we investigated orthodontic implant migration using micro-CT ( 6 ). The data suggested that bone resorption took place mainly in areas at which pressure was suspected to occur, whereas newly formed bone was observed at the initial implant positions.…”