Out of 102 university students initially considered, 24 of them suffered from myalgia (myalgia group) and 25 participants did not have any TMD-related symptom of signs (control group). When comparing anxiety, personality and coping variables between groups, the myalgia group presented greater levels of trait anxiety and neuroticism in comparison to the control group. In addition, participants with myalgia also showed higher levels of Acceptance and Resignation as well as Seeking Alternative Rewards, and in general they used significantly more often avoidance coping strategies, which was the only reliable predictor of DTM according to the logistic regression model.
The simplest result of this study is that out of the 102 individuals initially considered, 24 of them suffered from myalgia which formed the myalgia group, although the majority of these participants did not consider it severe enough to request professional help. Only 25 participants did not present any TMD-related symptom or signs. It should be noted that the participants were university students (a specific subgroup of young adults) and a more representative sample would have increased the study validity. Nevertheless, the percentage of students suffering TMD matches population prevalence suggested by other studies [15,36,37,38,39]. Furthermore, participants average score of the psychological questionnaires were similar to other Spanish university students (Spain) according to norms provided by questionnaire manuals [30,31,32], since percentiles where within 40 and 60 (see Table 2), except for anxiety trait and just one of the CRI coping strategy, logical analyses (30 and 35, respectively). In addition, the sample selection (a cohort of university students) favored the homogeneity of the samples in terms of age, sociological, cultural and environmental variables. Nonetheless, it should be taken into account that even though the myalgia group clearly fulfilled the diagnostic criteria, they weren’t severe patients seeking consultation. The fact that psychological alterations are already present in non-severe patients would support their importance in chronic and more severe TMD patients.
In accordance with previous studies in TMD, the myalgia group showed higher levels of trait anxiety than the control group [4,6,10-12,40] However, while the OPPERA prospective cohort study detected significantly larger levels of trait and state anxiety for TMD patients , in the present study state anxiety differences were not significant. This might be due to a high level of homogeneity between the myalgia and control groups, a cohort of university students, which were probably facing similar social and environmental demands. Alternatively, this could also be due to a lack of power resulting from the number of participants, since data analyses for anxiety scores revealed small size effects and powers. In addition, the present sample included participants suffering exclusively from myalgia. According to the present data, higher anxiety levels in myalgia might appear mainly because of the individuals’ traits, regardless of the situation, at least for young adult students.
A relationship between TMD and the Neuroticism personality trait has been previously observed . In the same line the OPPERA study showed that it is at least a predictor of TMD , however it did not differentiate between articular and muscular TMD pathologies. In the studies in which the differences between muscular TMD and articular TMD are analyzed, differences appear. Thus, Ferrando et al.  showed that myofascial patients present higher levels of neuroticism, whereas conscientiousness and self-discipline were higher in the articular group. Similarly, the present findings show that myalgic participants have larger levels of neuroticism than controls. It should be considered that personality is a psychological construct developed during the childhood-adolescence which is quite stable throughout life , therefore it might be scarcely affected by the curse of a disease. Taken the later in account, these results suggest that neuroticism might be an important personality factor contributing to TMD, at least for myalgia. Nonetheless, although neuroticism is often considered a stable personality trait depending on genetic and environmental factors , emotionally focused therapies, such as the unified protocol for the treatment of emotional disorders , might be useful to prevent TMD.
Coping styles were thoroughly investigated by means of the CRI inventory in the present study. The myalgia group used avoidance coping strategies significantly more often. Particularly, Acceptance and Resignation as well as Seeking Alternative Rewards were more prevalent in myalgia group than in the control group. Furthermore, according to the logistic regression model, Avoidance Coping is the best and only significant predictor of TMD. Therefore, it could be said that myalgic patients, in comparison to controls, tend to face a problem by looking for distractions, avoiding the problem and accepting that they can do nothing to solve it. Avoidance coping strategies are often regarded as maladaptive. Furthermore, maladaptive coping is related to depression and anxiety, . TMD patients seem to cope with stress differently than individuals from the general population. In line with the present findings, an increase of escape-avoidance strategies for TMD patients has been previously described, which were interpreted as maladaptive [18,20]. In this line, a recent study found that avoidance and passive coping strategies might worsen oral health-related quality of life in patients with myalgia . In contrast, some studies have observed higher levels of active coping in masticatory muscle pain patients in comparison with articular pain patients [27,28,46], although a symptomless control group was not included, making comparisons harder to establish. In contrast to previous research, the present study did not identify reduced adaptive coping strategies in the myalgia group. It should also be considered, however, that the participants were young students presenting myalgia, unlike previous studies, where the lack of adaptive coping strategies might well appear as a consequence of long lasting and more severe TMD and/or aging. Nonetheless, the differences in the assessment and definition of coping strategies across the few studies in the literature that assess coping in TMD make similarities hard to establish.
The way people face problems or stressful situations and the way in which they interpret them, may play a role in TMD, particularly in myalgia. Our data appears compatible with this hypothesis, as it indicated larger levels of avoidance/maladaptive coping styles in myalgic patients in comparison to the control group. In addition, it was the only reliable predictor of TMD according to the logistic regression model. The well-known OPPERA study investigated pain coping, but not stress-related coping strategies. however, they established that perceived stress increased the risk of first-onset TMD [4,46,47]. Specifically, maladaptive coping strategies might increase perceived stress, a strong predictor of TMD [48,49], thus playing a role in TMD. Therefore, intervention programs including techniques to promote the use of adaptive coping strategies, reduce maladaptive ones and foster emotional stability, which is related with neuroticism trait, may be useful to prevent the development of temporomandibular myalgia.
The present study points out that coping styles might be related with myalgia, although several limitations should be addressed in future research. A sample of dentistry students guarantees, on the one hand, the accuracy of symptoms detection (because of their symptoms awareness, and their knowledge about them), and on the other hand, it also equalized, educational level, similar environment and lifestyle between myalgic participants and controls. However, as discussed above, case group included young students presenting myalgia, even though they clearly fulfilled the diagnostic criteria, they weren’t severe patients seeking consultation. Therefore, further research including patients and a larger and more heterogenic sample of people could enhance the generalizability of the results. In addition, psychological factors, including depression, emotional intelligence and catastrophizing among others, should be investigated taking into account the TMD subtypes proposed by the new DC/TMD classification.