There is a high risk of external apical root resorption (EARR) following the application of intrusive orthodontic forces to the apical root. However, there is a lack of suitable animal models to study this phenomenon in depth. This study compared the usability of three different types of loops, namely, vertical helical loop, box loop, and L loop, for preparing a rat model of orthodontic tooth movement with invasive forces. Results showed a significant downward movement in the first molar of the rat after L loop placement for 14 days. Three-dimensional reconstructed images showed root resorption and length shortening on the apical root and decreased bone volume and trabecular thickness in the alveolar bone under compression. Histological staining revealed odontoclasts on the root resorption fossa. This study showed that orthodontic tooth movement using the L loop provides an effective experimental animal model of EARR.
Keywords: EARR; Intrusion; L loop; Orthodontic tooth movement model; Orthodontics.