Effects Of Increasing Occlusal Vertical Dimension On HMGB1 And IL-33 Expressions In The TMJ Condyle Of Adolescent Rats

Background and objectiveBoth occlusion and temporomandibular joint(TMJ) are important parts of the stomatognathic system.The relationship between occlusion and temporomandibular joint has long been of interest.An altered occlusion can cause the reshaping and adaptation of the temporomandibular joint,which is regulated by many cytokines.The mechanism of this process has not been fully understood.Increasing occlusal vertical dimension(i OVD)has been found to result in degeneration of the mandibular condyle in rats and higher expression of pro-inflammatory cytokines in synovial tissues,which suggests that there is an inflammation in the TMJ.High mobility group box-1 protein(HMGB1)and interleukin-33(IL-33)have been identified as alarmins that mediating danger signals.The expressions of both proteins increase in arthritis.HMGB1 and IL-33 can affect the metabolic activity in bone tissue and lead to joint destruction.However,there are few studies describe their functions in TMJ.The aim of this study was to evaluate the responses of mandibular condyle to i OVD.Material and methodsSixty-four male Sprague-Dawley(SD) rats at the age of 5 weeks were randomly divided into experimental(i OVD)and control groups.In experimental groups,occlusal vertical dimension was increased by bonding a 2-mm thick resin splint to the left and right maxillary molars.The animals in the control groups had a sham procedure under anesthesia.The animals in both groups were sacrificed on days 7 and 14 after splint insertion.Mandibular condyles were harvested for making sections and RNA extraction(n = 8).Histological observation was performed after hematoxylin–eosin(HE)staining.The expressions of HMGB1 and IL-33 were investigated by immunohistochemistry.The m RNA levels of Hmgb1 and Il-33 were assessed by real-time PCR.Results(1)There were no obvious differences in body weight and general condition between the control and i OVD groups.The resin splints showed good retention.(2)The results of HE staining showed that no pathological change was observed in the experimental groups.The thickness of the anterior and middle part of condylar cartilage in the i OVD group was thinner than that in the control group7 days after splint insertion(P < 0.05).On the 14 th day,there was an increasing trend in the thickness of the anterior,middle,and posterior part with no significant difference compared with the control group.(3)The expression of HMGB1 in the mandibular condyle of the i OVD group showed an increase compared with the control group on days 7 and 14.HMGB1 mainly occurred in the nucleus.The expression of IL-33 was very low in both control and i OVD groups.(4)The mRNA level of Hmgb1 in the mandibular condyle of the i OVD group was significantly higher than that in the control group on days 7 and 14(P < 0.05).The m RNA level of Il-33 showed no significant difference between each group.Conclusions(1)Bonding resin to the left and right maxillary molars is an effective way to establish an animal model of i OVD.(2)Increasing occlusal vertical dimension can lead to the adaptive remodeling of mandibular condyle and change the thickness of condylar cartilage in adolescent rats.HMGB1 may play an important role in the process of condyle remodeling.