| dc.description.abstract | Temporomandibular disorders (TMD) comprise a category of chronic complaints of pain and/or mobility dysfunction of the orofacial region. The main symptoms are pain from the temporomandibular joint and/or in the masticatory structures – sometimes radiating to the temples, head, and neck - clicking sounds from the temporomandibular joint, and restricted movement of the jaw. Psychological characteristics of TMD patients are mainly elevated levels of psychological distress, a relatively low correlation between physiological parameters and severity of pain and suffering, and interference with ability to perform activities of daily life due to pain or fatigue. <br><br>
In population samples, TMD occurs about twice as frequently in women as in men. The range of prevalence of TMD in the adult population has been estimated as 3-15%.<br><br>
The etiology of TMD is poorly understood. As is the case with other chronic musculoskeletal pain disorders, TMD seems to be best explained from a biopsychosocial perspective, in which it is viewed as a psychophysiological disorder involving changes in endogenous regulatory pain pathways, resulting in maladaptive emotional, physiological and neuroendocrine responses to physical and psychological stressors. Several studies have been performed of each of the factors assumed to contribute to the development of TMD. This thesis aims to extend previous research by elucidating possible, yet unexplored, group differences between TMD patients and healthy controls. <br><br>
Paper I:
Personality traits may be associated with illness and somatic symptoms in several ways.
First, personality traits may determine the perception and appraisal of pain and bodily sensations and whether these sensations are interpreted as a threat to health and physical function. Second, personality traits may determine health behaviour and thereby indirectly affect one’s health. Third, coping with symptoms and illness and adherence to treatment regimes may be influenced by personality traits. However, most studies have concentrated on measuring only one or two personality traits.<br><br>
Many TMD patients seem to exhibit a higher than average prevalence of psychological symptoms, e.g., anxiety and depression, compared to healthy controls. Moreover, TMD patients tend to report higher levels of pain from anatomical sites other than the orofacial region and higher levels of somatic symptoms like fatigue and dizziness than do healthy controls. One limitation of previous research is the failure to account for the possible influence of personality traits on general symptom report. Another limitation is the lack of control for the impact of acute pain sensitivity on general symptom report.<br><br>
Papers II and IV:
Several current theories of the development of chronic craniofacial pain emphasize the pathogenic role of central sensitization, i.e., increased firing rates or lowered firing thresholds of central nervous system (CNS) neurons. Relative to healthy controls, fibromyalgia syndrome (FMS) patients may exhibit lower pain thresholds after isometric exercise while no group differences are detected at baseline. These results may be interpreted as evidence of central sensitization and/or dysregulated endogenous pain control mechanisms in FMS. The symptom similarities between TMD and FMS indicate that these mechanisms of altered pain sensitivity may generalize to TMD, although this possibility has not been investigated. <br><br>
The organism is able to attenuate pain through complex endogenous control mechanisms originating in the cortex and brainstem, acting on nociceptive traffic at several sites of the spinal chord and brainstem. One endogenous pain regulatory mechanism subjected to increasing scientific interest the last two decades is the analgesic properties of cardiovascular (CV) system responses. Chronic pain groups do not seem to demonstrate the pain-attenuating effects of increased CV response levels. However, it is not known if all types of experimental pain stimulation are related to CV responding. Previous studies have employed ischemic and thermal pain, whereas pressure pain, which is assumed to be more similar to the clinical pain suffered by TMD patients, has not been investigated in relation to CV responding in chronic pain patients. <br><br>
Paper III:
The narrow focus on electromyography (EMG) as the preferred method for detecting physiological changes of relevance for the development or maintenance of chronic pain conditions ignores the multitude of central, systemic and local mechanisms that may be involved in this process. Detection of skin blood flow (SBF) changes in the orofacial region seems to be a promising method for identification of physiological changes that may contribute to the development of chronic musculoskeletal pain.<br><br>
Methods<br>
This project is based on two experiments. In the first study (Papers I-III), 25 female TMD patients and 25 healthy females matched for age, level of education, smoking, and exercise participated. They participated in a psychophysiological experiment where mean arterial pressure (MAP), heart rate (HR), EMG, and SBF were registered continuously while a reading aloud task, an arousing simulated job-interview, a computer game, and a biting task inducing masticatory load were performed. Between these experimental tasks, acute pain was induced by electrocutaneous stimulation of the left hand and pressure stimulation against the right masseter muscle and the sternum. At repeated intervals during the experiment, affective state was assessed. After the experimental session, the participants filled in questionnaires on somatic and psychological health complaints and personality traits. <br><br>
In the second study (Paper IV), 39 healthy females participated. The physiological registration and the pain stimulation were the same as in the first study. After a series of pain stimulation trials, the participants underwent the same arousing simulated job-interview as in the first study, whereupon several more pressure pain trials were performed. At repeated intervals during the experiment, affective state was assessed. After the experiment, the participants filled in questionnaires on somatic and psychological health complaints and personality traits. <br><br>
Results<br>
In Paper I, The TMD patients exhibited a lower level of Extraversion and Openness. In addition, there were higher levels of psychological distress and musculoskeletal pain in the TMD group relative to the control group. Hence, the typical TMD profile of affective distress and extra-craniofacial pain was reproduced. Importantly, these differences were maintained after controlling for Neuroticism, self-presentation bias, and acute pain sensitivity, putting previous research in this field on a more secure footing. <br><br>
In Paper II, relative to the control group, the TMD group exhibited a significantly higher electrocutaneous pain threshold and non-significantly lower pressure pain thresholds at baseline. After isometric contraction of the jaw, the TMD group exhibited increased general pain sensitivity. This did not occur in the control group. The arousing job interview did not significantly affect the subsequent pain sensitivity in any group. Significant positive correlations between MAP and pain thresholds and tolerance were seen only in the TMD group, a finding at variance with results from other studies using different pain stimulation methods.<br><br>
In Paper III, the cognitive tasks elicited significant MAP, HR, and SBF responses, and, overall, these were similar in the two groups. There were significantly lower levels of masseter EMG in the TMD group during relaxation, cognitive tasks, and jaw contraction, carefully suggestive of a pain adaptation process. Apart from a significantly lower masseter EMG in the TMD group during ipsilateral masseter pressure pain, there were no group differences in physiological responding during experimental pain stimulation. Relative to the controls, the TMD patients were more distressed during the experiment, as evidenced by their report of higher levels of state anxiety and depression as well as a more negative experience of the job-interview.<br><br>
In Paper IV, designed to explore some of the findings of Paper II in more detail, there was a non-significant trend of associations between MAP and HR and pressure pain sensitivity after the arousing job interview. Therefore, it is not possible to dismiss the CVR-pain relationship in normotensive, pain-free women altogether. <br><br>
Overall, this thesis has two major conclusions. First, the differences in personality traits, health complaints, and psychological distress between TMD patients and controls may be considerable, while physiological assessments may fail to discriminate between the two groups. Second, the indications of central sensitization processes in TMD patients suggest that this disorder may be regarded as a systemic illness and not as a focal problem of the orofacial region. | eng |