A Preliminary Study Of The Effect Of Severe Occlusal Attrition On The Peripheral And The Primary Nervous System Of Rat

Background：As a common chronic disease in dental clinic, severe occlusal attrition (SOA) is animportant cause of temporomandibular joint disorders (TMD). SOA is often accompaniedby pain, abnormal jaw movement, clicking and noise of temporomandibular joint (TMJ)and some other symptoms, among which masticatory muscles pain andtemporomandibular joint pain are the primary reasons for seeing a doctor of outpatients. Inliterature, previous basic studies associated with severe occlusal attrition mainly focusedon the reactions of oral local tissues, and confirmed that severe occlusal attrition can resultin adaptive remodeling of the masticatory muscles and temporomandibular joint. However,few studies focused on the orofacial pain and the reaction of related nervous systeminduced by severe occlusal attrition. In the models of other oral and maxillofacialneuropathic pain and inflammatory pain, the upregulated expression of calcitoningene-related peptide (CGRP) in the oral and maxillofacial peripheral sensory nerve center--trigeminal ganglion (TG), and the activated MAPK pathway and upregulation ofphosphorylation of p38(p-p38) protein in spinal nucleus of trigeminal nerve (SpⅤ) in thebrainstem and the medulla oblongata area, have been confirmed. Therefore, the presentstudy will focus on the threshold of orofacial pain and related reactions in nervous systeminduced by severe occlusal attrition.Objective：The present study aims at establishing and evaluating SOA animal model. Based onthis model, the pain sensitivity of rat masseter muscle, the changes of relatedneurotransmitters in trigeminal ganglia, brainstem and medulla oblongata, will beinvestigated.Methods：1.With the aid of surgical microscope, the animal model of SOA was established bygradually and evenly decreasing the crown height of the maxillary molars of rat, and thechange of weight and the phenotype in rats were observed, and the degree of pressure painsensitivity of the masseter muscles of rats was detected by behavioral methods.2.The changes of the CGRP expression level in rat trigeminal ganglia induced bySOA were analyzed by immunofluorescence staining.3.The changes of the p38MAPK expression levels in rat brainstem and the medullaoblongata induced by SOA were analyzed by immunofluorescence staining and westernblot.Results：1.With the help of surgical microscope, the animal model of SOA is successfullyestablished by gradually and evenly decreasing the crown height of the maxillary molarsof rats. No obvious phenotypic abnormalities in rats were found in SOA animals. On thethird day the pressure pain threshold of masseter muscle reduced significantly, which lasttill the21th day, and on the28th day the pressure pain threshold of masseter musclerecovered to baseline levels in SOA groups.2.The expression levels of CGRP increased significantly induced by SOA, which waslocated in the maxillary dental neurons of trigeminal ganglion area. On the third day after modeling, the number of CGRP-positive neurons significantly increased to a peak level. Inthe following3weeks the number of CGRP-positive neurons began to decrease, but stillsignificantly more than the control group. On the28th day it recovered to baseline levelsin SOA groups.3.Induced by SOA, p38MAPK pathway in SpⅤ of rat brainstem and the medullaoblongata was activated. The expression of p-p38increased significantly on the third dayafter modeling, and then began to decrease. The state of activation last3weeks, and on the28th day the expression level of p-p38recovered to baseline level.Conclusions：1.The SOA animal model is established successfully. Induced by SOA, the degree ofpressure pain sensitivity of the masseter muscles increases temporarily.2.Induced by SOA, the expression of CGRP in the maxillary dental neurons oftrigeminal ganglion area increased temporarily, which indicates that CGRP play animportant role in the development of pain.3.Induced by SOA, the expression of p-p38protein in SpⅤ of rat brainstem and themedulla oblongata related area increased temporarily, which indicates that the p38MAPKpathway be activated in this process.