RÉSUMÉ
Objective To explore the effect of cannabinoid receptor 2(CB2)on orthodontic tooth movement(OTM)rate and periodontal tissue reconstruction of pressure area in mice.Methods Thirty CB2-/-male mice and thirty littermate control WT male mice were individually accepted the orthodontic appliance at their age of 6 weeks.The mice were respectively scarified at 3 days,7 days,14 days and 21 days after the operation.Then the tooth movement distance was examined through the stereomicroscope.Hematoxylin-eosin staining was performed to explore the biological responses of periodontium at the distal mesial root pressure area.Anti-tartrate acid phospha-tase staining was performed to calculate the number and distribution of osteoclasts at the distal mesial root pressure area,and MMP-9 was evaluated by immunohistochemistry to examine the number of MMP-9(+)monocytes and multinucleated cells in the same district as the TRAP staining.Results Compared with those WT mice at 3,7,14 and 21 days,OTM distance showed a gradual increased tendency according with experimental time over 21 days.The widths of periodontal ligament on the pressure side were markedly greater in CB2-/-mice than WT mice at 7,14 and 21 days(P＜0.000 1).The numbers of TRAP positive osteoclasts were significantly greater in CB2-/-mice than those in WT mice at 14 days of OTM(P＜0.001).MMP-9 immunohistochemical staining showed that the number of MMP-9(+)monocytes and multinucleated cells was more in CB2-/-mice than that in WT mice at 14 days of OTM(P＜0.05).Conclusion The absence of CB2 accelerates orthodontic tooth movement under or-thodontic force.The absence of CB2 reinforces bone resorption in orthodontic tooth movement compressive area dur-ing orthodontic tooth movement.