Orthodontic Tooth Movement In Irradiated Rat Jawbones: Preliminary MicroCT Study

Objectives: Irradiation affects bone metabolism, which is a key feature for orthodontic tooth movement (OTM). We aimed to assess post-radiation OTM changes in bone-related features by micro-CT.
Methods: Thirteen-week-old rats received 5Gy external x-ray radiation to the whole head (n=11), while others served as control (n=11). Two weeks later, orthodontic appliance (NiTi spring, 20g) was activated in a split mouth technique for 2 weeks between left maxillary first molar and incisors after which animals were sacrificed. The harvested maxillae were scanned using micro-CT for assessing: distance of the OTM (µm), trabecular bone volume fraction (BV/TV, %), trabecular thickness (Tb.Th), porosity volume fraction (PoV/TV, %) and volumetric bone mineral density (vBMD) in 2 regions corresponding to the pressure and tension sides of the first molar.
Results: NO-OTM: irradiation caused increase in BV/TV and Tb.Th (19%, 14%, respectively, p<0.005) and 13% decrease in PoV/TV (p<0.005) compared to controls. In the controls, OTM induced decrease in vBMD and Tb.Th in the tension side (5%, 26%, respectively, p<0.005) with no difference in the pressure side. In the irradiated animals, OTM led to decrease in BV/TV in both tension and pressure sides (33% and 52%, respectively, p<0.05). OTM in irradiated rats was reduced by 30% compared to control (220.4±81.7µm and 313.0±76.2µm, respectively, p<0.002). Most morphometric parameters in OTM were similar between irradiated and control animals; the only different parameter was vBMD which was increased by 4% in the tension side of the irradiated group (p<0.05).
Conclusions: OTM in irradiated animals is smaller compared to animals that didn't undergo irradiation despite similar levels of resorption areas in the pressure side, suggesting defective bone turnover. Although radiation led to an increase in bone parameters presumably due to impaired bone resorption, orthodontic tooth movement “corrected” the bone microstructure resulting in similar parameters between the control and irradiated animals.