Change Of COX-2 And VEGF In Alveolar Bone Remodeling Stimulated By Low-intensity Pulsed Ultrasound

More and more adult patients with malocclusion are seeking to orthodontic treatment as people’s pursuit of beauty is getting higher and higher. But the long treatment period makes people feel annoyed. So how to shorten the time and accelerate orthodontic tooth movement become a research hotspot. The movement of teeth in orthodontic treatment depends on its periodontal tissue remodeling process, in which alveolar bone remodeling is the major one. Many studies have shown that low intensity pulsed ultrasound（LIPUS） can generate mechanical shock effect and effectively promote the expression of some cytokines, enzymes and induce cell osteogenic differentiation, It’s intensity < 100 mW/cm2 and greatly reduce the damage to tissue.In recent years,the LIPUS has caught the attention of researchers due to its advantages: noninvasive,cheap,safe.Some studies have proved that the expression of COX-2 and PGE₂ in osteoblast can increase rapidly under the mechanical stimulus of mechanical drawing, fluid force, LIPUS,which can activate a number of signal transduction pathways to regulate bone metabolism and remodeling.Meanwhile, Angiogenesis is essential in the process of fracture healing and bone remodeling,VEGF is an important factor for that. The study aims to evaluate the effect of LIPUS on the expression of COX-2、PGE₂ and VEGF and investigate the potential mechanism of the effect of LIPUS on alveolar bone remodeling in orthodontic treatment.Objective:1.To evaluate the influence of LIPUS on the movement of teeth in orthodontic treatment in rats.2.To evalute the change of COX-2 and PGE₂ in the process of alveolar bone remodeling stimulated by LIPUS.3.To evalute the change of VEGF and osteoclast in the process of alveolar bone remodeling stimulated by LIPUS.The study of the above indicators can provide experimental datas and theoretical basis for the potential mechanism of LIPUS effects on orthodontic tooth movement.Methods:Thirty male SD rats were randomized into control groups and LIPUS groups. The LIPUS groups took LIPUS（frequency 1.5 MHz, intensity 30mW/cm2, pulsewidth 200 μs, repetition frequency 1 KHz） by 20 minutes per day from the second day following animal models of orthodontic teeth movement,and the control groups took sham LIPUS treatment. The samples were collected on the 1st day, 3rd day, 5th day, 7th day and 14 thday respectively. General measurement analysis,Immunohistochemistry and TRAP staining were performed to evaluate the effects of LIPUS in the process of the alveolar bone remodeling.Results:1. The first molar movement distance of two groups were gradually increasing, the amount of tooth movement in experimental group was more greater（P <0.01）.2. The expression of COX-2 and PGE₂ in the periodontal ligament of two groups increased first and then reduced,the peak is the 7th day. The number of COX-2 and PGE₂ positive cells in experimental groups was greater（P <0.01）.3. The expression of VEGF and osteoclast in the periodontal ligament of two groups increased first and then reduced,the peak is the 7th day. The expression of VEGF in experimental groups was higher（P <0.01）.Conclusion:1. LIPUS can effectively promote the speed of orthodontic tooth movement.2. LIPUS may effectively increase the expression of COX-2 and PGE₂ to promote alveolar bone remodeling.3. LIPUS may effectively increase the expression of VEGF and osteoclast to promote alveolar bone remodeling.remodeling.