The Study On The Hypoxia Of Periodontal Tissue During Orthodontic Tooth Movement

Objective:Orthodontic tooth movement is a process in which periodontal tissue undergoes bone remodeling through a series of physiological reactions.Through the regeneration of the distraction side bone and the absorption of the pressure side bone,the goal of tooth movement is finally achieved.The vascular system in the periodontal ligament can provide oxygen and nutrients for orthodontic teeth to maintain normal physiological activities.When orthodontic force is applied to the teeth,the periodontal tissue on the pressure side is compressed and the tension side is stretched.During the whole process,the blood flow in the periodontal ligament is reduced.In turn,the periodontal tissue is in an ischemic state,which leads to a decrease in the partial pressure of oxygen,forming a local hypoxic environment.Hypoxia is a key factor in initiating bone remodeling,but there is still a lack of systematic research on the hypoxic state of periodontal tissue and its changing law.Therefore,it is of great significance to study the hypoxic state of periodontal tissue.It can provide a theoretical basis for the future study of the dynamic changes of the periodontal tissue microenvironment and the physiological reconstruction of periodontal tissue after orthodontic stress,and at the same time provide a new idea for the future use of hypoxia as a target to promote orthodontic tooth movement.Methods:1.The periodontal ligament stem cells are separated and cultured from the isolated teeth by the method of tissue mass,and the cultured periodontal ligament stem cells are observed through the primary culture,proliferation and passage.The cultured periodontal ligament stem cells are stained with alizarin red and alkaline phosphate Enzyme staining,oil red O staining,and alcian blue staining proved its ability to differentiate in multiple directions,and its source was identified by flow cytometry.2.Periodontal ligament stem cells are subjected to periodic tension stimulation with a frequency of 0.5 Hz and a deformation of 10%.The two techniques of qRT-PCR and Western blot are used to detect the gene and protein expression level of HIF-la in the periodontal ligament loading at 0h,12h,24h,and 36h.Using hypoxia-sensitive fluorescent probes to observe the degree of hypoxia in periodontal ligament cells under tension at 0h,12h,24h,36h.Using transmission electron microscopy to observe the the morphology of mitochondria in periodontal ligament under tension at 0h,36h.3.Establish a rat orthodontic tooth movement model,and detect the expression of HIF-la in periodontal tissues at 0d,1d,3d,7d,and 14d by immunohistochemical staining.Results:1.The periodontal ligament stem cells are successfully isolated and cultured.The periodontal ligament stem cells can be observed under an inverted microscope in a long spindle shape;the cells grow vigorously after passage,in good condition,and have the characteristics of fibroblasts.It has strong osteogenic,adipogenic,and chondrogenic abilities.The cell surface markers of periodontal ligament stem cells are detected by flow cytometry,which proves that they are cell populations derived from mesenchyme2.The morphology of periodontal ligament stem cells changes under tension and the cell morphology is stretched.Fluorescence quantitative PCR and Western Blot were used to detect HIF-1α in periodontal ligament stem cells at gene and protein levels,and the results were basically the same.After the cells are forced,the internal expression gradually increases with time;under the scanning electron microscope observation,the mitochondria in the cells are vacuolated and the endoplasmic reticulum swells in the sample under the force for 36 hours compared with the unforced sample;under the inverted fluorescence microscope It was observed that the green fluorescence intensity of the sample subjected to force for 12h,24h,36h was increased compared with the sample without force,which proved that the cells were hypoxic after force.3.The orthodontic tooth movement model was successfully constructed.The periodontal tissue of rats without force was weakly positive for HIF-1α,and the positive expression of HIF-1α in the periodontal tissue of rats was increased at 1d,3d,7d,and 14d after the force was applied.Conclusion:In this project,the periodontal ligament stem cells are loaded with tension,and through the application of molecular protein levels,cell microscopic morphology,and hypoxia probes,it further verifies that periodontal ligament cells are in a hypoxic microenvironment under the action of periodic tension..At the same time,through the establishment of the rat orthodontic force model in vitro,the histological level further verified that the periodontal ligament in the body is in a hypoxic environment under the orthodontic force.The experimental verification indicates that the tissue is in a hypoxic environment during orthodontic tooth movement,which provides a new idea for the future use of hypoxic microenvironment to study the bone remodeling mechanism during orthodontic tooth movement.