[A study on the effect of midface fullness on the overall perception of lip prominence]

Objective: To evaluate the influence of midface (nasal base and zygomatic bone) morphological changes on the overall perception of lip prominence from different perspectives. Methods: From February to March 2024, 212 volunteers were recruited in Fujian Province as study subjects and divided into three groups: orthodontists [65 participants, 28 males and 37 females, aged (31.3±6.9) years], orthodontic patients [72 participants, 24 males and 48 females, aged (27.6±5.7) years], and healthy adults [75 participants, 37 males and 38 females, aged (25.6±4.4) years]. Three-dimensional facial modeling software was used to generate facial models, which were sculpted using three-dimensional model sculpting software to simulate different nasal base, zygomatic bone, and upper lip prominence conditions. A total of 15 facial models were generated, divided into five groups (three models per group): Group A (normal nasolabial angle, normal nasal base, normal upper lip); Group B (increased nasolabial angle, normal nasal base, flattened upper lip); Group C (decreased nasolabial angle, normal nasal base, protruded upper lip); Group D (increased nasolabial angle, protruded nasal base, normal upper lip); Group E (decreased nasolabial angle, recessed nasal base, normal upper lip). Models 1, 2, and 3 in each group had normal, protruded, and flattened zygomatic bones, respectively (with Model 1 in Group A as the initial model). Forty-five-degree and ninety-degree profile images of the models were captured (30 images in total) and compiled into a questionnaire. Participants in the three study groups were selected as the most attractive and least attractive facial appearances based on the questionnaire and ratings of the lip prominence of the 45° and 90° profile images (0-10 points, where 0=very flat, 5=normal, and 10=very prominent). A one-sample t-test was used to compare the difference between model ratings and the median score of 5. Results: Among the 30 images, the proportion of lip prominence ratings deviating from the median score of 5 was the highest among orthodontists [83% (25/30)], followed by orthodontic patients [67% (20/30)], and lowest among healthy adults [53% (16/30)]. At the 90° profile view, the scores given by orthodontists, orthodontic patients, and healthy adults for the initial model (5.07±0.79, 5.00±1.03, and 4.95±1.07, respectively) showed no statistically significant difference from 5 (t=0.65, P=0.521; t=0.00, P=1.000; t=-0.42, P=0.673). At the 45° profile view, the scores given by orthodontists, orthodontic patients, and healthy adults for the initial model (5.42±0.98, 5.40±1.15, and 5.35±1.45, respectively) were significantly higher than 5 (t=3.30, P=0.002; t=2.98, P=0.004; t=2.11, P=0.038). At both 90° and 45° profile views, orthodontists, orthodontic patients, and healthy adults all rated the lip prominence of Model 1 in Group E (nasal base recession) significantly higher than 5 (all P<0.05). In Group E (nasal base recession model), changes in zygomatic prominence led to alterations in the overall lip prominence ratings by orthodontists and orthodontic patients, with significant differences among Models 1, 2, and 3 (all P<0.05). In the most attractive facial appearance evaluation, Model 1 of Group D had the highest frequency percentage in both the 90° profile and 45° profile views [90°: 19.8% (42/212); 45°: 22.6% (48/212)]. Conclusions: Orthodontists had the highest sensitivity to changes in lip prominence. The observation angle influenced the perception of lip prominence changes, and variations in zygomatic and nasal base prominence could shift lip prominence evaluations. A slightly larger nasolabial angle, protruded nasal base, and normal zygomatic bone configuration were perceived as the most attractive.