Fig. 6. NAC retards orthodontic tooth movement and suppresses the expression of IL-1β and TNF-α in rat PDL tissues. (A) Illustration for the design of orthodontic tooth movement. The mesial movement of the maxillary first molars was induced by applying closed nickel-titanium spring. To examine the effect of antioxidants on tooth movement, a split-mouth design was used. Daily injection of 50 μl of antioxidant (Res 200 μg, NAC 25 mg) or vehicle (Veh) was performed in the buccal mucosa adjacent to the mesial surface of the first molar. Seven days after appliance placement, the rats were sacrificed. Arrow shows the direction of tooth movement. I; incisor, M; molar. (B) Representative micro CT images of vehicle-treated group: (upper) occlusal view, (lower) buccal view. The micro CT images of maxilla were obtained and reconstructed three dimensionally. (C) The distance between the mesial fossa of first molar and the distal fossa of the third molar was measured. The data represent the mean ± S.D. of five independent experiments. *p < 0.05. (D) Horizontal slices of the decalcified specimens were prepared, and immunohistochemical staining for IL- 1β and TNF-α was performed. Scale bar = 50 μm. -Ab, staining without primary antibody; R, root; B, alveolar bone.