Mentolabial angle and aesthetics: a quantitative investigation of idealized and normative values

Background: This study is a quantitative evaluation of the influence of the mentolabial angle on perceived attractiveness and threshold values of desire for surgery. Methods: The mentolabial angle of an idealized silhouette male Caucasian profile image was altered incrementally between $84^{\circ}$ and $162^{\circ}$. Images were rated on a Likert scale by pretreatment orthognathic patients (n = 75), lay people (n = 75) and clinicians (n = 35). Results: A mentolabial angle of approximately $107^{\circ}$ to $118^{\circ}$ was deemed the most attractive, with a range of up to $140^{\circ}$ deemed acceptable. Angles above or below this range were perceived as unattractive, and anything outside the range of below $98^{\circ}$ or above $162^{\circ}$ was deemed very unattractive. A deep mentolabial angle ($84^{\circ}$) or an almost flat angle ($162^{\circ}$) was deemed the least attractive. In terms of threshold values of desire for surgery, for all groups, a threshold value of ${\geq}162^{\circ}$ and ${\leq}84^{\circ}$ indicated a preference for surgery, although clinicians were least likely to suggest surgery. The clinician group was the most consistent, and for many of the images, there was some variation in agreement between clinicians and lay people as to whether surgery is required. There was even more variability in the assessments for the patient group. Conclusions: It is recommended that in orthognathic and genioplasty planning, the range of normal variability of the mentolabial angle, in terms of observer acceptance, is taken into account as well as threshold values of desire for surgery. The importance of using patients as observers in attractiveness research is stressed.