To investigate the difference of the temporomandibular joint between patients with anterior open-bite and normal overbite with cone beam CT (CBCT).

Fifty-four patients with anterior open bites and 54 patients with normal overbites were selected from the Department of Orthodontics, Nanjing Stomatological Hospital, Medical School of Nanjing University from June 2014 to August 2020. Sagittal and coronal images of the temporomandibular joint were reconstructed with multiplanar reconstruction techique. The Kamelchuk method was used to measure the superior, posterior and anterior space of the temporomandibular joint, and the condylar morphology was divided into two types: normal and abnormal. The joint space and condylar morphology of the anterior open-bite group and the normal overbite group were statistically analyzed. The anterior open-bite group was divided into 3 subgroups: ① Ⅰ° open-bite (open bite distance < 3 mm), ② Ⅱ° open-bite (open bite distance ≥3 mm and ≤5 mm) and ③ Ⅲ° open-bite (open bite distance > 5 mm). The difference of overbite spaces of the temporomandibular joint was compared among these three subgroups.

Compared to the normal group, no significant differences were found for the anterior and superior space of the temporomandibular joint in the anterior open-bite group (P > 0.05), but the posterior space increased significantly (P < 0.01). A total of 52.8% of patients in the anterior open-bite group had abnormal condyles, whereas 21.3% of patients in the normal group, overbite significant differences was found between the two groups (P < 0.01). Compared with patients with Ⅰ° and Ⅱ° openbite, the condyle of patients with Ⅲ° open bites was more forward in the fossa (P < 0.05).

The position of the condyle in the fossa of patients with anterior open bites is more forward, and abnormal condylar bone is more common found.