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.

BACKGROUND:Reactive oxygen species is a double-edged sword in the development of periodontitis and the regeneration of periodontal tissue.Low concentration of reactive oxygen species induces the differentiation of periodontal fibroblasts,and excessive reactive oxygen species will cause damage to periodontal tissue.In the process of inflammation,the accumulation of reactive oxygen species in periodontal tissue induces damage to cells and tissues through a variety of signaling pathways or through redox reactions. OBJECTIVE:To review the double-edged sword effect of reactive oxygen species in periodontitis and periodontal tissue regeneration,thereby providing potential targets and treatment ideas for the clinical treatment of periodontitis and periodontal tissue regeneration. METHODS:Databases of CNKI and PubMed were searched for relevant articles published from April 1990 to April 2023 with the key words of"periodontal tissue engineering,periodontal defect,regeneration of periodontal tissue,chronic periodontitis,reactive oxygen species,oxidative stress,antioxidative stress,oxidative injuries,free radicals,reactive nitrogen species"in Chinese and English,respectively.By reading the titles and abstracts,repetitive studies or irrelevant literatures were excluded.Finally,77 articles were included for review. RESULTS AND CONCLUSION:Reactive oxygen species are a kind of free radicals with high reactivity.When bacteria invade,reactive oxygen species are released in large quantities by the respiratory explosion of neutrophils and play a double-edged sword role in the body through their redox reactions or as pleiotropic physiological signal transmitters.In periodontitis,low concentrations of reactive oxygen species can kill invading pathogenic bacteria,but high concentrations of reactive oxygen species promote the secretion of inflammatory factors through JNK,RANK,Wnt/β-Catenin and other pathways,promote immune damage or directly damage tissues through oxidative reactions or through other ways to aggravate periodontitis.In the process of periodontal tissue regeneration,low concentrations of reactive oxygen species can promote the proliferation and differentiation of periodontal ligament stem cells through Nrf2 and other pathways and can promote the secretion of vascular endothelial growth factor to promote vascular regeneration.This provides seeds and a nutrient environment for periodontal tissue regeneration,which is extremely important for promoting periodontal tissue regeneration.However,high concentrations of reactive oxygen species will reduce the activity of periodontal ligament stem cells and damage endothelial cells,which are not conducive to vascular regeneration.This will inhibit wound healing and periodontal tissue regeneration.Therefore,it is important to explore the role of reactive oxygen species in the development of periodontitis and periodontal tissue regeneration and to discover the potential mechanism of its action and to explore the appropriate concentration for its role in reducing periodontal inflammation and promoting periodontal tissue regeneration for the future treatment of periodontitis and periodontal tissue regeneration in clinical practice.Using reactive oxygen species as a target to explore ways to reduce periodontal inflammation and promote periodontal ligament stem cell activity and vascular regeneration may become a clinically effective method for treating periodontitis and promoting periodontal tissue regeneration.