Temporomandibular disorders : incidence, course, and risk factors

Abstract: Temporomandibular disorders (TMD) embrace pain and dysfunction in the temporomandibular joint (TMJ) and jaw muscles. TMD is a prevalent condition in the population and constitutes a significant health problem. Knowledge of factors influencing the onset and course of TMD is important in preventive care and development of treatment strategies as well as in clinical decision making. The aim of this thesis was to gain knowledge of whether variations in dental occlusion, bruxism, spinal pain and gender predicted the development and course of TMD. The study population comprised 371 undergraduate dental students. A questionnaire was used to obtain case histories. Clinical examination included the function of the TMJ, jaw muscles, maximal jaw mobility, the morphological occlusion, and contact patterns in centric and eccentric positions. The examinations were performed at start, and after 12 and 24 months. In total, 280 subjects were examined at all three occasions. The incidence of TMJ pain and dysfunction was high among both males and females. The course composed onset, recovery and maintenance resulting in a fluctuating pattern. Females were more likely to have persistent TMJ pain and dysfunction than males. The incidence and persistence of jaw muscle signs and symptoms was high and significantly more common in females. A similar fluctuating pattern as for TMJ pain and dysfunction was found. Crossbite predicted onset and persistence of TMJ pain and dysfunction; mandibular instability in centric positions predicted persistent TMJ pain and dysfunction, as well as persistent jaw muscle signs or symptoms. Reported bruxism increased the risk for TMJ pain and dysfunction but did not significantly affect the course of jaw muscle signs and symptoms. Spinal pain at baseline predicted the onset of jaw pain, headaches, and TMD pain. Signs of TMD at baseline predicted the onset of non-pain symptoms of TMD, jaw pain, headaches, and spinal pain. In conclusion, the results in this thesis show high incidence rates for TMD, headaches, and spinal pain among dental students. Crossbite, mandibular instability, reported bruxism, as well as female gender were identified as contributing risk factors. Spinal pain and TMD mutually predicted each other, indicating common pathophysiological mechanisms and individual vulnerability. The findings support a multidisciplinary approach, and it is recommended that the status and function of the jaw system be considered in patients with spinal pain.