MusculoskeletalPsychological stress may contribute to temporomandibular joint disorder in rats

BackgroundPsychological stress is considered a possible pathogenic factor for temporomandibular joint disorders (TMJD), but few reports have supplied direct evidence. This study was designed to observe the effects of psychological stress on the masticatory muscles and condylar processes in rats to directly investigate the role of psychological stress in TMJD morbidity.Materials and methodsA well-established rat communication box model was used to compare the myoelectric profiles of temporal and masseter muscles and condylar microstructure among rats in a control group, a psychological stress group (PS group), and a diazepam (anxiolytic agent) injection group (PS + DI group). Reverse-transcription polymerase chain reaction was also used to analyze the substance P mRNA and calcitonin gene-related peptide mRNA levels expressed in condylar cartilages during different phases of psychological stress.ResultsAt 1, 3, and 5 wk, both temporal and masseter muscles in the PS group exhibited a significantly higher electrical potential in relaxation than those in the control group (P < 0.01). The electrical potential during contraction of the temporal and masseter muscles was higher than in the relaxation or control group at 1, 3, and 5 wk (P < 0.01). Scanning electron microscopy demonstrated pathologic changes in condylar processes in the PS group that were not observed in the PS + DI group. Reverse-transcription polymerase chain reaction also showed that the expression of substance P and calcitonin gene-related peptide in rat temporomandibular joint was upregulated during each phase of the psychological stress (P < 0.05).ConclusionsPsychological stress may play an important role in the formation of TMJD.