The reliability of analytical reference lines for determining esthetically pleasing lip position: An assessment of consistency, sensitivity, and specificity

Introduction This study aimed to identify a simple yet reliable soft-tissue parameter for the clinical determination of esthetic lip position by investigating the most consistent reference lines and assessing their sensitivity and specificity. Methods A total of 5745 records from Chinese patients aged >18 years were screened. In part I of the study, lateral view photographs of 96 subjects (33 males, 63 females) with esthetic facial profiles were selected. The profile esthetics of each photograph was first scored by 52 dental students, followed by 97 laypeople on a 5-point attractiveness scale. For the top 25% of photographs with the highest score for each sex (8 males, 16 females), the consistency of 6 commonly used reference lines were assessed to determine the esthetic lip position. In part II of the study, lip positions relative to Steiner’s (S) and Ricketts’ (E) lines in the profile photographs of 86 patients (43 males, 43 females) deemed to have an esthetically unpleasing profile were compared with those in 86 Chinese movie star idols (43 males, 43 females). Results In part I of the study, the S, E, and Burstone’s (B) lines exhibited the lowest standard deviations for the upper and lower lips. B line was excluded from further analysis because of its higher mean absolute values, and S and E lines were used for the subjective assessment in part II of the study. In part II, the S line showed a sensitivity of 86.0% and 86.0% and a specificity of 81.4% and 83.7% for males and females, respectively. In contrast, the E line presented a sensitivity of 88.4% and 93.0% and a specificity of 79.1% and 74.4% for males and females, respectively. Conclusions S, E, and B lines were the most consistent soft-tissue parameters among both sexes; however, because of the smaller absolute values, the S line would be more convenient among the 3 for a quick clinical assessment of lip position. Moreover, the performance of both S and E lines was similar among both sexes, which supports using these lines in assessing the esthetic lip position.