Effect of Orthodontic Movement in Recovery Phase of Experimental Periodontitis

Objectives: It is largely unknown whether orthodontic movement induces periodontal bone loss (PBL) after treatment of periodontitis. This study was to investigate the effect of orthodontic movement in the recovery phase of ligature-induced periodontitis in a mouse model.
Methods: C57BL/6 mice (male, 8-week old) were divided into three groups (n=8). Silk ligatures (SL) were tied around the maxillary right (group 1) or both (groups 2&3) first molars on Day 0, removed on Day 8, and systemic antibiotics (SA) were administered through drinking water (group 3) since Day 8. Orthodontic force (OF) was applied on the maxillary right first molars since Day 13 (groups 2&3). All mice were sacrificed on Day 20. PBL palatal and mesial to first molars, and the closest distance (CD) between the first and second molars were evaluated by histomorphometry. Gingival cytokine (RANKL, OPG, IL-10, TNFa, IL-1b) expressions were determined by RT-qPCR.
Results: PBL palatal and mesial to the first molars was significantly larger on SL side vs. control side in group 1. Palatal PBL was marginally increased on OF+SL side vs. SL alone side in group 2, whereas no such difference was observed in group 3. All mice in groups 2&3 showed detectable movement of right first molars, but no difference in CD was observed between group 2 and group 3. Gingival RANKL/OPG expression ratios were identical in SL side compared to control side in group 1, whereas the ratios were significantly increased in OF+SL side vs. SL alone side in groups 2&3. Gingival expressions of IL-10, TNFa and IL-1b were up-regulated on OF+SL side vs. SL alone side in group 3.
Conclusions: We established a mouse model of orthodontic movement/ligature-induced periodontitis. Orthodontic movement may induce borderline PBL in the recovery phase of periodontitis, which can be abrogated by antibiotic administration without affecting tooth movement.