[The clinical study on occurrence of TMJ dysfunction in orthodontic patients]

Occlusal disharmony is considered to be the most significant factor of temporomandibular joint (TMJ) dysfunction, but the relationship between malocclusion and TMJ dysfunction has been unknown yet. The purpose of present study was to investigate the relationship between TMJ dysfunction and occlusal disharmony (eccentric occlusal contacts and functional shift of the mandible) in orthodontic patients. The subjects were 533 orthodontic patients, 209 males and 324 females, who were received at the Department of Orthodontics, School of Dentistry, Hokkaido University from April 1985 to March 1988. Their ages ranged from 8 to 38 years old. All were prior to orthodontic treatment. The results were as follows 1. The prevalence of TMJ dysfunction was 27.6%, 24.9% in males and 29.3% in females. The difference was insignificant between males and females. 2. The patients with TMJ dysfunction increased after 13-15 years old, corresponding to dental age IV A (Hellman's classification). 3. In patients with TMJ dysfunction, the highest frequency of symptom of TMJ dysfunction was joint sounds (77.6%), the second was pain (22.4%), the third was disturbance of mandibular movement (4.8%). The complication of those symptoms were compounded in 26.3% of the total patients. 4. The prevalence of TMJ dysfunction had no relation to specific malocclusion and maxillofacial morphologic characteristic. 5. Most patients with TMJ dysfunction had occlusal disharmony (95.9%). 6. Eccentric occlusal contacts were found most frequently in patients with open bite and functional shift of the mandible was found most frequently in patients with deep bite. From these findings, the prevalence of TMJ dysfunction was frequent in orthodontic patients, however the symptoms were objective and the patients were not aware of TMJ dysfunction. TMJ dysfunction had no relation to specific malocclusion but some kinds of occlusal disharmony were easy to occur in specific malocclusion and TMJ dysfunction was induced by those etiological factors.