Reciprocal influence on the incidence of symptoms in trigeminally and spinally innervated areas.

Temporomandibular disorders (TMD), headaches, and spinal pain show co-morbidity and may therefore influence each other. The hypothesis tested is that the presence of any of these conditions will increase the risk of onset of new symptoms within a 2-year period. The study population comprised 280 dental students, who were examined three times at 12-month intervals. The incidence was calculated for a 2-year period, based on subjects without the defined symptom at baseline. Each participant was classified into five different case-control groups, representing incidence cases or no incidence (controls) of: (1) nonpain TMD symptoms; (2) jaw pain; (3) headaches; (4) spinal pain; and (5) TMD pain. Presence of headaches and of spinal pain and signs and symptoms of TMD at baseline were used as independent variables in logistic regression analyses, controlling for age and sex. Incidence cases with TMD pain reported spinal pain at baseline significantly more often than the controls, and were mostly women. Incidence cases with headaches and incidence cases with jaw pain significantly more often had signs of TMD and reported spinal pain at baseline, compared to controls. Incidence cases with nonpain TMD symptoms or spinal pain significantly more often presented with signs of TMD at baseline. Our findings show that pain and dysfunction in trigeminally innervated areas and pain in spinally innervated areas mutually predict the onset of new symptoms in dental students, indicating common pathophysiological mechanisms and individual vulnerability. This may be of importance in risk assessment and treatment planning of individuals with musculoskeletal pain.