Effect of Midline Deviation and Crown Width Disproportion on Perception of Smile Esthetics

To evaluate the effect of maxillary midline deviation and crown width disproportion on the perception of smile attractiveness through full-face images among dentists and laypeople.

A full portrait image of a smiling 25-year-old female, exhibiting good dental alignment, midline position, and tooth size symmetry, was selected as a model for the present study. The original image was digitally modified using photo editing software (Photoshop CC, Version 25.12.0; Adobe) to simulate three different case scenarios of varying levels: Midline deviation (1-4 mm), single crown width disproportion, separately for central incisor, lateral incisor, and canine (1 and 2 mm), and crown width disproportions distributed to anterior teeth (1-4 mm). In total, 15 modified images were displayed randomly to 180 observers (90 laypeople and 90 dentists) including the original image that served as a control. Each observer scored the level of smile esthetics for each image using a visual analog scale ranging from point 0 (unattractive) to 100 (attractive). Bonferroni Test and Partial Eta Squared were utilized for the statistical data analyses (α < 0.05).

Attractiveness scores were significantly lower for the modified smiles with the single crown width disproportion than distributed crown width disproportion and midline deviation (p < 0.001 for each), of which two presented statistically similar attractiveness (p = 0.278). The highest attractiveness scores were obtained for the control image (90.35 ± 5.56^A), midline deviation of 1 mm (88.89 ± 5.93^AB), 2 mm (86.80 ± 6.70^ABC), and distributed disproportion of crown width of 1 mm (87.75 ± 6.70^AB). A single central incisor disproportion of 2 mm (45.51 ± 11.94^I) was perceived significantly less attractive, followed by a midline deviation of 4 mm (57.51 ± 12.58^H) and a distributed disproportion of crown width of 4 mm (59.11 ± 9.72^H). Modified images were perceived as significantly more attractive by laypeople and male observers compared to dentists and female observers (p < 0.001 for each). Older observers between 35 and 50 years old scored significantly higher than younger observers (p = 0.001).

Dentofacial midline discrepancy had less effect on smile attractiveness compared to crown width disproportions. Midline deviations up to 2 mm were not noticeable for both laypeople and dentists. The deviations of 3 mm were noticeable but still more attractive than the deviations of 4 mm, which were considered the least attractive. A single crown width disproportion was less perceived when moving from the central incisor toward the canine. Distributing the crown width disproportions among anterior teeth can be beneficial for smile attractiveness compared to non-distributed cases.

Generating symmetrical crown width proportions of the anterior teeth seems more important for smile esthetics than dentofacial midline harmony. Distribution of crown width disproportions among the anterior teeth can enhance smile esthetics.