Abstract
The prolabium is an anatomical element which forms the free margin of the upper lip and greatly contributes to the creation of the impression of individual facial features. In this study, the author analyzed the morphology of the prolabium at rest in 100 healthy young Japanese men and women (mean ages : male, 9.6 years ; female, 26.8 years), and compared the results with previous statisitical data. At the same time, angles formed by the main components of the circumference of the prolabium of the upper lip, which are important for morphological classification, were also measured. After reference points established by the author were directly measured on standard photographs of upper lips, mean values and standard deviations were calculated, and differences between men and women, and between ages, and correlations between parameters were determined. The internal oblique margin of the upper vermilion and the width of the rima oris were significantly larger in men (p<0.01), whereas the beta and gamma angles were significantly larger in women (p<0.05) . There were no statistically significant differences in other parameters, including the height of the upper vermilion, the maximum height of the upper vermilion, and alpha and delta angles. There were no statistically significant differences between ages in the twenties and in the thirties. There was marked correlation between the height of the upper vermilion and the maximum height of the upper vermilion in both men and women, suggesting that comparison of the individual thickness of the prolabium of the upper lip can be based on either one of these 2 parameters. However, the maximum height of the upper vermilion seemed to be more relevant to the evaluation of the thickness of the prolabium of the upper lip. Both men and women showed correlation between alpha and beta angles; namely, the larger the angle alpha, the larger the angle beta, making the margin of the prolabium less clear. From these results, it was thought that young Japanese tend to give the impression that their prolabium have steep lateral margins and thick median regions because their alpha angle was larger while their beta and gamma angles were smaller than those of women. In contrast, young Japanese women appeared to have prolabium of the upper lip with gentle-slope and soft lateral margin, causing the impression of thin median region.
