Histological response of the periodontal tissue to mandibular incisor movement using clear aligners of varying thickness in a rabbit model

Objective: Investigate the histological response of the periodontal tissue to incisor movement using varying-thickness clear aligners in a rabbit model. Methods: Thirty-three New Zealand rabbits were randomly assigned to two experimental groups (0.38-mm and 0.68-mm aligners) and a control group. Each rabbit in the experimental group wore three sequential aligners, which were changed every 5 days. Orthodontic force was measured using a uniaxial force sensor, and tooth movement was quantified using three-dimensional imaging. Root resorption was assessed using micro-computed tomography. Histological and immunohistochemical staining and real-time quantitative reverse transcription polymerase chain reaction tests were performed to evaluate the periodontal tissue response. Results: The 0.68-mm aligners generated larger forces than the 0.38-mm aligners. Tooth movement was faster with the third 0.38-mm aligner, with no statistically significant differences between the two groups. Both groups exhibited minor root resorption, with the 0.68-mm group exhibiting larger resorption craters. Additionally, the 0.68-mm group demonstrated more significant deformation of periodontal fibers and increased expression of inflammatory markers. The 0.38-mm group showed a larger number of osteoclasts on the compression side. Conclusions: Both aligners achieved effective tooth movement. The 0.38-mm aligners exerted smaller forces and enabled slightly faster movements than the 0.68-mm aligners. Although both groups showed minimal root resorption, the 0.68-mm group exhibited larger resorption craters. Furthermore, the 0.38-mm group exhibited less histological deformation and inflammation in the periodontal tissues. These results suggest that aligner thickness can be tailored to customize treatments. Further studies with longer observation periods and more refined methodologies are warranted.