Growth of lips in two dimensions: a serial cephalometric study.

The effect of growth on the cross-sectional area of the lips was studied radiographically on 168 lateral cephalometric films of 28 persons, taken every 2 years from the age of 8 to the age of 18 years. All subjects studied had received no orthodontic treatment, and the total lip outline as it is seen on the lateral cephalogram was traced and calculated by computerized cephalometry. This method of calculating the total lip area, instead of relating lip growth to a single lip point, was selected in order to avoid any effect that positional changes of the lips may have and subsequently superimpose on lip changes resulting from growth. Increase in total lip area, in both numerical and proportional terms, was observed from age 8 to age 18 years. The largest incremental growth increase for both lips took place between the ages of 12 and 14 years, while no significant changes were observed after the age of 16. Tested growth changes for sex differences revealed statistically significant sexual dimorphism, with larger maxillary lip area in males at ages 10, 12, 14, 16, and 18 and larger mandibular lip area at 18 years of age, while the females showed significantly larger mandibular lip area at age 12.