Quantitative evaluation of lip symmetry in skeletal asymmetry

The objective of this study was to investigate whether skeletal mandibular asymmetry associated with unilateral and anterior crossbite will lead to lip asymmetry. The subjects were 26 females, 13 controls and 13 true skeletal asymmetric age-matched patients (24-50 years). The study group was diagnosed as asymmetric according to visual and panoramic radiographic examination and exhibited a unilateral anterior crossbite, an asymmetric mandible, and a deviation of the chin. The control group was visually symmetric and exhibited all forms of tooth malalignment without the presence of a crossbite. Digitized images of the frontal facial photographs of all the subjects, taken in an intercuspal contact position, were analysed for upper and lower lip symmetry pre- and post-orthodontic treatment. The upper and lower lips were subdivided into two quadrants each and the surface area of each quadrant was measured and expressed as a percentage of the total surface area of the relevant lip. The degree of lip asymmetry was obtained by calculating the difference in percentage area between the two quadrants of each lip. In the study group, the lower lip quadrant on the crossbite side was increased pre-treatment (56.85 +/- 1.75 per cent), while the contralateral side was reduced (43.15 +/- 1.75 per cent, P < 0.005), resulting in 13.7 per cent asymmetry. After treatment, the respective lip areas were 52.12 +/- 0.64 and 47.88 +/- 0.64 (P < 0.01) and asymmetry was significantly reduced (4.25 +/- 1.29 per cent). In the control group, the differences between the lower lip quadrant areas (range 48.5-51.5 per cent) were small (less than 3 per cent asymmetry) and did not change post-treatment. The findings demonstrate that in this study group, lower lip symmetry was mainly controlled by the support provided through the dental interarch relationships and less by skeletal factors.