In general, craniofacial pain and disability is a health problem that affects a large population. TMD fall into this category (10). The most common symptom of TMD is pain, which is usually present in the masticatory muscles, areas around the ears, eyes, throat, and temporomandibular joint, as well as cause pain in head and neck. In addition to pain, patients with TMD usually have limited or asymmetrical jaw movements and jaw sounds such as click, pop, and crepitus (11). Stress is considered as one of the main etiological factors in dysfunction of the masticatory system(2). Dental students are often more stressed during their training than the general population(6). In this study the relationship between occupational stress and TMD was investigated by measuring salivary cortisol and immunoglobulin A levels in students Dental School. According to our results, the mean score of DES questionnaire in students was 2.48 ± 0.58. There was only a significant difference between the academic years and evaluation of clinical performance by the professor (p = 0. 03) that in fifth year students was significantly higher than fourth- and sixth-year students. There were no significant differences between other parameter in this study. In several studies, similar to our study, the factors of exams, fear of falling and not passing the courses among the students of different dental schools are the most stressful factors (12–15). Also, it has been reported that female students had a higher stress than male students. Higher stress in girls can be attributed to issues such as feeling more pressured to succeed, receiving less support from friends, and girls being more vulnerable(12, 14, 16).
Cortisol is considered the physiological marker of stress. When stress is perceived by the individual, the HPA(Hypothalamic–pituitary–adrenal) axis is activated and the end result is the secretion of cortisol from the adrenal glands. Measuring cortisol saliva is a reliable tool for measuring the activity of the HPA axis(7). The correlation between salivary cortisol and plasma cortisol is greater than 0.9(17). Therefore, salivary cortisol can be considered equivalent to serum, and salivary cortisol is used today as a stress index, and like plasma cortisol, the concentration of salivary cortisol is a reliable marker for stress(18). Secretory IgA in saliva is the main immunological factor at the mucosal level and has been shown to be sensitive to psychological variables(19). The circadian rhythm of salivary secretory IgA concentration is closely related to the circadian rhythm of salivary cortisol(20). Salivary secretory IgA has been used in several studies as a stress marker(8). In our study there were no correlation between these markers’ levels with DES questionnaire score and TMD. Vivian Ng reported that students with more stress had higher salivary cortisol levels before the exam(21). In other study, more stress was associated with significantly lower IgA concentration in saliva(19). In this study, 24 patients (40%) had TMD, although no significant correlation was found between TMD and three variables of cortisol level, IgA level and DES questionnaire score. In some studies showed that people with TMD have significantly higher levels of stress and anxiety(1, 7). The lack of significant differences between our findings may be due to small sample size. In the present study, the prevalence of TMD was 40%. In similar studies the prevalence of TMD was 54%(22) and 58%(23). The difference in the prevalence of TMD may be due to diagnostic criteria and the use of different scales. Prevalence of articular sounds in our study were similar to Mahshid and Wieckiewicz studies (24) (23).