Prevalence of degenerative disease of the temporomandibular joint in anterior open bite patients with different molar relationships: a retrospective observational study

Objectives: To assess the prevalence of degenerative disease of the temporomandibular joint in anterior open bite patients with different molar relationships. Methods: 246 anterior open bite adult orthodontic patients were divided into Class I group ( n =65), Class II group ( n =116) and Class III group ( n =65) based on their sagittal molar relationships, meanwhile, 70 normal subjects were selected as control group. The occurrence of degenerative joint disease was detected by cone beam computed tomography, and the prevalence of degenerative joint disease among groups was compared. Mandibular plane angle and the vertical distance between the upper and lower incisors were also measured. Results: The overall prevalence of degenerative joint disease in anterior open bite patients and control group was 30.28% and 5.00%, respectively. Class II group showed the significantly highest prevalence of degenerative joint disease (50.43%, P ＜0.001), highest frequency of bilateral degenerative joint disease (43.95%， P ＜0.001) and highest mandibular plane angle. Among the anterior open bite groups, Class III group exhibited the highest vertical distance between the upper and lower incisors (3.35 ±1.86mm, P ＜0.05) but the lowest prevalence of degenerative joint disease(10.77%). Conclusions: For Class II anterior open bite patients, condylar resorption in degenerative diseases of TMJ may be an important cause of malocclusion.