Acceptable esthetic limits for maxillary dental midline shift and mandibular asymmetry: Who notices what and how much?

Introduction: This study aimed to evaluate maxillary dental midline shifts and mandibular asymmetries created in different amounts and directions on photographs taken from 7 different angles by different groups and to determine acceptable esthetic limits.

Methods: Photographs of a female model in a social smile position were taken from 7 different angles (0° [frontal], 15°, 30°, and 45° on the right and left sides) and digitally modified for maxillary dental and mandibular midline deviations at specified degrees using Adobe Photoshop. To enable participants to evaluate the photographs sequentially, the photographs were transformed into videos using Adobe Premiere Pro software. The videos were rated by 188 participants (48 orthodontists; 49 dentists; 45 esthetic, plastic, and reconstructive surgeons; and 46 laypersons) using the visual analog scale (VAS) in a survey. An analysis of variance test was used to compare VAS scores among raters, and the Bonferroni test was used to compare VAS scores among the groups.

Results: The threshold for the acceptability of maxillary dental midline shifts was 2 mm for orthodontists; dentists; and esthetic, plastic, and reconstructive surgeons but 4 mm for laypersons. Although laypersons were unable to perceive changes in mandibular asymmetry between 0°-6°, the threshold was 3° for other groups. For participants in which mandibular asymmetries and maxillary dental midline shifts were in opposite directions, the threshold for all groups was 6°. For participants in which lower jaw asymmetries and maxillary dental midline shifts were in the same direction, the threshold value for orthodontists was 6°. Other groups could not perceive variables related to asymmetry.

Conclusions: More sensitive esthetic assessments can be made by evaluating smile esthetics from different angles. Mandibular asymmetries are considered more esthetically acceptable than maxillary dental midline shifts. In mandibular asymmetry and maxillary dental midline shifts, deviations in the same direction are more esthetically acceptable than deviations in opposite directions. Orthodontists are able to notice small changes in mandibular asymmetry.