| One of the important etiological factors of temporomandibular disorders (temporomandibular disorder, TMD) is abnormal occlusion.The preliminary study results show that,the effect of gradually induced disordered occlusion (GIDO) can lead to temporomandibular condylar cartilage abnormal construction,or even degeneration. In the present study rats were used to establish an animal model of abnormal occlusion,characterized as gradually induced disordered occlusion,and their temporomandibular joint (TMJs) were steined with HE and also with antibodies of TNF-α,OPG,RANKL using histochemistry method to observe the changes in the condylar cartilage.The cartilage thickness was measured.The expression of TNF-α,OPG,RANKL in condylar cartilage was calculated by the area of positive cells percentage.The purpose of the present study was to investigate the effect of occlusion abnormity to condylar cartilage cells proliferation,differentiation and enchondral bone formation.Fourty-eight SD rats,aged 8 weeks,with same gender distribution,were divided into experimental and control groups at random,and further divided by four times points,three in each subgroup in male and in female. For the rats in experimental groups an elastic rubber band was inserted between the first and second mandibular lower and maxillary upper molars, to movethe first molar medially.Four weeks later the third mandibular lower and the third maxillary upper molars were moved distally with same method. In this way the GIDO was established in rat.For the rats in control groups nothing was done for the occlusion and raised in the same environment. Experimental group and control group rats were sacrificed at the end of 2th,4th,6th,8th week respectively.HE staining and immunohistochemistry staining were taken with antibodied of TNF-α,OPG and RANKL.The results are as follows:1.There is no difference in condylar cartilage thickness between right and left sides and between male and female rats.So the datas were pooled bilaterally and for bothe sexes.The control group condylar cartilage thickness gradually decreased with age. Those in 12-,14-,16-week subgroups were thinner than 10-week subgroup (P <0.05),and 16-week old subgroup thiner than 12-week subgroup ( P = 0.035),but not than 14-week subgroup (P> 0.05).For the rats in 4-,6-,8-week subgroups in experimental group the condylar cartilage thickness were thicker than the age matched control group (P <0.05),but 2-week subgroup was not (P = 0.23).The cartilage in 6 week experimental subgroup was significantly thicker than those in 2-,4-,8-week subgroups (P <0.05),while there were not significantly different between the latter three groups (P> 0.05).2.TNF-αmainly concentrately expressed in hypertrophic layer.In control groups it showed gradually increased with age (P <0.05). Those in 2-,6-,8-week experimental subgroups were significantly higher than that of the age matched control subgroups,and the 6-,8-week subgroups were higher than 2 week subgroup (P <0.05).There was no significant difference at 4 week subgroup between those in experimental and control groups (P> 0.05).No difference between males and females.3.OPG expressed mainly in the hypertrophic layer.In the control groups its expression showed the trend of decreasing with age (P <0.05).In female experimental group those in 2-,4-,6- and 8-week subgroup calculated by the area of positive cells percentag showed an significant increasing trend, higher than the age matched contraol (P <0.05).It was more significant in the 6-week subgroup (P = 0.001).The difference in 2-,4-,6-week (P <0.05),but not in the 8 week (P = 0.472) , male subgroups in the experimental group were significantly higher than the control groups.4.RANKL concentrately expressed in hypertrophic layer.Male and female of the experimental group showed the following regularities.RANKL expressed in the 2-,6-,8-week subgroups were significantly higher than the age matched control groups (P <0.05),but those in the 4 week subgroup did not (male:P = 0.201,female:P = 0.467).Female 6- and 8-week subgroups expressed stronger than 4 week subgroup (P <0.05) but 2 week subgroup did not (P = 0.342).Male 2-,6-,8-week subgroup expressed stronger than 4 week subgroup (P <0.05)Conclusions:1.Gradually Induced Occlusal Disorders (GIOD)can lead to degenerative change in TMJs together with increased proliferation, and the degenerative changes increased with time and extension of the disorders of occlusion.2.TNF-α,OPG and RANKL all play an important role in the remodling of condylar cartilage induced by occlusal disorders.
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