Abstract: Objective:To study furtherly on the pathogenesis and the characteristics of craniomandibular disorders （CMD）.Methods:Animal models of the overextended opening and the traumatic occlusion were established for this study. And the histopathologic observations of the temporomandibular joint （TMJ） and masticatory muscle, immunohistochemical staining of substance P （SP） and prostaglandin E₂（PGE₂） in TMJ soft tissue, and radioimmunologic analyses of PGE₂ and PGE_2α in masticatory muscle were performed and the pathogenicity of these two pathogenic patterns was compared.Results:（1）Overextended opening and traumatic occlusion resulted in some injury to TMJ and masticatory muscles. Among the injured tissues, the disc attachment and correlative masticatory muscles underwent the most obvious traumatic changes. （2）There were some differences in the injury sites depending on the particular pathogenic pattern. The lowerhead of the lateral pterygoid muscles and the temporalises showed greater changes of injury in the overextended opening groups, while the upper head of the lateral pterygoid muscles and the masseteres produced more notable changes of injury in the traumatic occlusion groups. Conclusion:The pathogenesis and the pathological characteristics of CMD can be affected by different pathogenic patterns.