Is there a greater mandibular movement capacity towards the left? Verification of an observation from 1921

In 1921, the German dentist Hans Wertheim reported that more individuals were able to shift the mandible more towards the left than to the right. This study analyses the deviation from symmetrical mobility of the lower jaw in either direction. Using a millimetre ruler, maximum jaw opening (MJO), maximum left laterotrusion (MLL), and maximum right laterotrusion (MRL) were recorded in 141 healthy individuals and in 141 patients with temporomandibular disorders (TMDs). For both sexes, the mean maximum movements to the left and to the right were greater in the healthy group as compared with the TMD group. Healthy subjects as well as patients were able to move the mandible more to one side. Only a minority had identical values for MLL and MRL. The majority of healthy individuals and TMD patients could move more to the left (P < 0.001). In the healthy group, the mean ratio between MJO and MLL was 5.0, and 5.5 between MJO and MRL. In the TMD group, the corresponding values were 4.6 and 6.1. The mean absolute difference between MLL and MLR (in mm) was 1.24 [95% confidence interval (CI): 0.99; 1.49] among healthy females, and 2.09 (95% CI: 1.52; 2.66) among healthy males. In the TMD group, the corresponding values were 2.62 (95% CI: 2.21; 3.04) and 2.83 (95% CI: 1.67; 4.00), respectively. From the results of our study we conclude that moderate deviations from symmetric movements (mean: 1.2 mm for women, 2.1 mm for men) appear to be the norm even in healthy individuals.