A comparison of five cephalometric planes evaluating lower lip position

Objectives: To determine which, if any, of five commonly used lip profile planes best describes horizontal lower lip orthodontic treatment changes. Methods: Pretreatment and post-treatment cephalograms of 79 patients 12.4±2.8 years of age, including 22 female nonextraction cases, 16 female extraction cases, 22 male nonextraction cases, and 19 male extraction cases. For each patient, nine landmarks were digitized twice on separate occasions and averaged. Lower lip (labrale inferiorus) changes over time were measured relative to five lip profile planes, including Burstone's B line, Sushner's S2 line, Rickett's E line, Holdaway's H line, and Steiner's S1 line, using Viewbox 3.0 software. As independent measures of treatment change, the horizontal changes in infradentale, lower incisor tip, and labrale inferiorus were measured relative to a stable reference plane registered on sella and oriented on the SN-7„a. Results: The five profile planes showed no significant sex differences in the treatment changes. While all five profile planes measured greater treatment effects for extraction than nonextraction cases, only Holdaway's H line demonstrated statistically significant group differences. The E line (s2=2.66mm) showed the greatest variation among the subjects, while the H line (s2=1.28mm) showed the least variation. While lip changes based on the five profile planes demonstrated moderately high to high inter-correlations, ranging from 0.81 to 0.97, they showed only weak correlations (r<.35) with the horizontal changes of infradentale and labrale inferiorus. Conclusions: While all five planes measured a similar aspect of positional change, none of them closely reflected the actual lower lip changes that occurred. This research was supported by Baylor Oral Health Foundation.