Layperson assessment of smile lines and upper lip combined images in smile esthetics

Abstract

The esthetic assessment of smile lines by laypersons is a subject of ongoing debate. However, smile lines often appear with different types of upper lip curvature, which further complicates the esthetic assessment process, and studies on this combination are lacking. The purpose of this clinical study was to investigate a layperson's esthetic perception of smile lines and upper lip combined images. Twenty-six smile images resulting from combinations of 3 upper lip types, 4 anterior smile line types, and 3 posterior smile line types were generated by an image editing software program. Eighty-three laypersons (39 men and 44 women; 18 to 35 years of age) completed rating images using a visual analog scale. Unattractive smiles were designated to be those with scores <50 and attractive ones with scores ≥50. Data were analyzed using 1-way analysis of variance and Bonferroni post hoc tests (α=.05). High anterior smile line with gingival display >4mm obtained significantly lower scores of <50 when combined with all upper lip curvatures (upward: 28.29 ±22.79, straight: 38.74 ±23.00, downward: 30.67 ±22.25, P<.01). High anterior smile lines with gingival display ≤4mm combined with upward and straight upper lip curvature images obtained significantly higher scores, and all were ≥50 (upward: 63.24 ±22.22, straight: 61.40 ±21.58, P<.01). From a layperson's perspective, high anterior smile lines with gingival display >4mm combined with any lip type were determined to be unattractive. If gingival display was ≤4mm combined with both upward and straight lip types, the smile was assessed as attractive.