Experimental Study On The Effect Of Propranolol And Isoproterenol On Orthodontically Induced Root Resorption In Rats

Tooth movement is started and facilitated by mechanical force,in which alveolar bone exists remodeling including bone resorption in the compression side and bone formation in the tension side,in which root resorption may exist.Orthodontic-induced root resorption,as a kind of orthodontic complications,caught the attention of more and more scholars.Related research showed that the factors in the process of orthodontic root resorption were complex and diverse,including gender,age,hormone,gene,and the size of the force,drugs,ultrasonic,laser,etc.Its factors need further study.The sympathetic nervous system not only plays an important role in regulating the cardiovascular system and internal organs function,but also participates in the bone remodeling process.The sympathetic nervous system canincrease the RANKL expression in the osteoblasts by activating the beta 2 adrenergic receptors on the surface of the osteoblasts through a series of signal transduction,thus stimulating osteoclast differentiation and mature to increase the bone resorption.Root resorption and bone resorption is similar,both including inorganic acidification and organic matter degradation process,which is induced by osteoclasts and cementoclasts respectively.Osteoclasts and cementoclastssh are the similarity in morphological structure and physiological function,whether the sympathetic nervous system affects root resorption by cemenclasts,it worth research.Therefore,it means a lot to orthodontic patients whether sympathetic nervous system affects root resorption during the orthodontic tooth movement and how.Purpose:By the orthodontic tooth movement animal model,this research aimed to study the effects of propranolol(PRO)and isoproterenol(ISO)on the root resorption and the mechanism.We try to prove that more attention should be given to the psychotic and neurotic condition of the orthodontic patients.Methods:Thirty-six specific-pathogen-free Sprague-Dawley rats were selected to establish model of orthodontic tooth movement.Then rats were divided into three groups according to the random number table:PRO group,ISO group and the control group.Each group included twelve rats.Rats in each group were intraperitoneally injected with PRO(20mg/kg/d),ISO(5mg/kg/d)and isometric saline.The nickel titanium coil was activated once a week to keep the force.The rats were sacrificed by heart perfusion fixation method after 14 days.Then the maxillary first molar and the alveolar bone arounding were separated and 6 specimens in each group were selected made into slices after decalcification.The slices were treated with three dying methods:1.HE staining:to observe the histological changes of periodontal membrane-and the surface of root and the alveolar bone.2.TRAP staining:to count the specifically stained cementoclasts.3.RANKL immunohistochemical staining:to calculate the mean optical density value of the specifically stained RANKL.4.MicroCT scanning:the left maxillary first molars of the left 6 specimens in each group were carefully extracted and were scanned by MicroCT.Then the mean volumes of the mesial root in each group were calculated.Statistical analysis of experimental data were finished by SPSS 19.0 statistical software.Results:1.Overall observation:during the experiment,the weight of the rats went down from the 1th to 4th day due to the operation trauma,diet inconvenience,and so on.The rats started to gaining weight from the5th day.All the rats were included in the study.The mean weight of the rats showed no differences among the three groups(P<0.05).2.HE staining:the results showed that the periodontal membrane space in the pressure side in each group became thinner and the continuity of the root surface were destroyed.Various size resorption pits and the multinucleated giant cells could be observed on the pressure side of the root.The degree of root resorption and the depth and scope of the root resorption pits in each group were various.The dentine could be involved in serious area.The degree of root resorption in the PRO group was slighter than the control group.The degree of root resorption in the ISO group was severer than the control group.3.TRAP staining:the TRAP staining positive cells were large and showed irregular morphology,red cytoplasms and blue nuclei.They mainly existed in the resorption pits in the pressure side of the cementum and the alveolar bone,arranging in a line.The analysis of results of TRAP staining showed that the number of TRAP staining positive cells in PRO group was lower than that in the control groups(P<0.05).The number of TRAP staining positive cells in ISO group was larger than that in the control group(P<0.05).4.Immunohistochemical staining:RANKL positive area were cytoplasms.The positive expression of RANKL was visible in the pressure side of the periodontal tissue,and differences existed among groups.The analysis of RANKL expression on the root surface using analysis software showed that the value of RANKL expression in the PRO group was less than that in the control group(P<0.05);and the value of RANKL expression in the ISO group was higher than that in the control group(P<0.01).5.MicroCT scanning:the surface of the root of extracted maxillary first molar was unsmooth and uneven.By mearsurent,the mean volume of mesial root of the maxillary first showed significant difference.The mean volume of mesial root in PRO group was larger than that in control group(P<0.01).The mean volume of mesial root in ISO group was smaller than that in control group(P<0.05).Conclusions:1.?2 adrenergic receptor antagonist can lessen the cementoclast on the pressure side to reduce the root resorption during the tooth movement;while the agonist did the opposite.2.SNS can affect the root resorption through ?2 receptor during tooth movement in rats.3.SNS can regulate the expression the RANKL through ?2 receptor to affect the root resorption during the tooth movement in rats.