The relationship between temporomandibular joint effusion and pain in patients with internal derangement. 
The purpose of this study was to evaluate the relationship between temporomandibular joint (TMJ) effusion and joint pain in patients with internal derangement based on the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD).  A total of 240 TMJs from 120 patients with unilateral painful joints (103 females and 17 males, mean age 29.9 ± 12 years) were evaluated.  Clinical assessments were carried out according to the DC/TMD guidelines.  Magnetic resonance imaging (MRI) was used to evaluate the degree of effusion in each joint.  The radiological and clinical findings were analysed for statistically significant correlations.  Although the results indicated a statistically significant association between moderate joint effusion and disc displacement (p < 0,05), there was no statistically significant association between moderate effusion and joint pain (p > 0,05).  There were, however, statistically significant associations between marked effusion and both disc displacement and joint pain (p < 0,05).  TMJ effusion is associated with both disc displacement and joint pain: the effusion increased in direct proportion to the severity of pain and disc displacement.  The possibility that there are various aetiologies for the condition should also be considered.