Balkwill angle, mandibular occlusal plane angle and temporomandibular joint morphology: a retrospective study

The shape and structure of the temporomandibular joint (TMJ) can be affected by many factors and occlusal factors are considered important factors. Although many scholars have studied the correlation between the occlusal plane (OP) and TMJ morphological characteristics in different types of malocclusion, it is still unclear whether the Balkwill angle and mandibular occlusal plane (MOP) angle affect the TMJ morphology. The aim of this study was to investigate the correlations between the Balkwill angle, the MOP angle and TMJ morphology in adults with skeletal Class II Division II malocclusion using cone-beam computed tomography (CBCT).

Seventy adult patients (29 males and 41 females, mean age 23.32 ± 3.22 years) with no symptoms of temporomandibular disorders were divided equally into two groups: skeletal Class II division II low angle-study group (14 males, 21 females, 23.66 ± 3.29 years) and skeletal Class I average angle-control group (15 males, 20 females, 22.98 ± 3.15 years). The Balkwill angle, OP angle (FH-OP), MOP angle (FH-MOP), DPO (vertical distance from the condylar center to the MOP) and TMJ measurement items were measured.

The mean values of FH-OP and FH-MOP angles were smaller in the study group (P < 0.05), while the average values of Balkwill angle and DPO were larger in the study group than in the control group (P < 0.05). Significant differences were found in the condylar mediolateral diameters, condylar head width, articular eminence inclination and height, and superior joint space between the two groups. The correlation analysis showed that the Balkwill angle was strongly positively correlated with DPO and negatively correlated with MOP angle. In the control group, the Balkwill angle, MOP angle and DPO had weak correlations with TMJ morphology. However, in the study group, the Balkwill angle, MOP angle and DPO had moderate correlations with TMJ morphology.

The DPO had a significant impact on TMJ morphology, followed by the MOP angle, and finally the Balkwill angle in skeletal Class II Division II low angle malocclusion.