Quantitative investigation of the esthetic impact of lip prominence in relation to the esthetic line

Introduction

The purpose of this quantitative investigation was to assess the influence of lip prominence in relation to the esthetic line (E-line) on perceived attractiveness and threshold values of desire for treatment.

Methods

The lip prominence of an idealized silhouette male white profile image was altered incrementally between −16 mm to 4 mm from the E-line. The images were rated on a Likert scale by pretreatment orthognathic patients (n = 75), laypeople (n = 75), and clinicians (n = 35).

Results

In terms of perceived attractiveness, lips to E-line distance within the ranges of −12 mm to −16 mm and 0-4 mm in relation to the E-line was associated with a reduction in median attractiveness scores to below 4 in the patient and clinician groups of observers; for the lay group, the corresponding ranges were −14 mm to −16 mm and 2-4 mm. Relative lip prominence appears to be viewed as more attractive than lip retrusion. Clinicians were generally least likely to suggest treatment for varying levels of bilabial position. For a number of the images, there was reasonable agreement among clinicians and laypeople regarding whether treatment is required. For the clinician group, the only categories for desire for treatment were at a lip to E-line distance within the ranges of −14 mm to −16 mm and 2-4 mm.

Conclusions

It is recommended that the range of normal variability of the prominence of the lips and threshold values of the desire for treatment be considered in planning.

Highlights

  • The study provides attractiveness data for lip prominence in relation to the Ricketts esthetic line.

  • The values described may serve as a database for facial analysis.

  • Lip prominence is an important parameter for orthodontic and orthognathic surgical planning.

The relative prominence or retrusion of lip position within the face is thought to be a significant facial esthetic parameter. The prominence and/or size of the lips can be altered directly, for example, by surgical reduction of the vermilion or alternatively lip augmentation with fillers; or indirectly, by the sagittal movement of the maxillary and mandibular incisors, the associated dentoalveolus, or orthognathic surgery, which has a variable effect on lip prominence because of inherent soft-tissue variability.

For any given population, lip prominence will have an average value or norm , specific for age, gender, and ethnicity, and an associated range of normal variability, with appearance concerns, often resulting from a significant deviation of the sagittal lip position from the accepted norm for the population. For clinical diagnosis and treatment planning, it is important to know at what point the deviation of lip prominence moves from an acceptable range of variability to being perceived as a facial deformity. The magnitude of the deviation, whether it is due to the underlying dentoalveolar framework, the soft-tissue thickness, or a combination of the 2, is an important factor in deciding when orthodontic treatment and/or surgery may be required. If the magnitude of the discrepancy of bilabial prominence or retrusion is great, the treatment planning decision may be relatively straightforward. However, a significant number of patients are regarded as borderline in terms of the need for treatment. In such patients, the decision-making process may be transferred from subjective clinical judgment to objective, evidence-based guidance on the basis of the data from studies investigating perceptions of bilabial positional attractiveness.

One of the most well-known analyses for lip prominence is the esthetic line (E-line) described by Ricketts , over 50 years ago as part of his computerized cephalometric analysis. It is worth noting that the vast majority of the Ricketts analysis is dentoskeletal, but he also described the E-line (nose-chin line) as joining the tip of the nose and the most prominent point on the soft-tissue chin in profile view, and based on his data derived from analysis of 1000 patients (600 females, 400 males) with an average age of “about nine years,” provided the average value of the distance from the lower lip to the E-line as −2 mm. Positive values would be with the lower lip ahead of the E-line. There is considerable sagittal and vertical growth of the nose and lips after the age of 9 years, and as such, the lips will tend to move in a negative direction relative to the E-line. Ricketts conceded that considerable individual variation existed, but his general view was that the upper lip should be approximately 4 mm and the lower lip 2 mm behind the E-line in an average white adult.

Although Farkas et al , provided average values for many facial parameters, on the basis of anthropometric studies, unfortunately, he did not anthropometrically measure bilabial prominence. However, a number of modern authorities have provided ideal values for bilabial prominence, based either on anecdotal evidence and the good eye of the respective clinician, data from treated patients, or normative values from growth data. Riolo et al did not evaluate bilabial prominence; however, Bhatia and Leighton provided values of between −4 mm to −6 mm (± 2 mm) in adult males and approximately −5 mm (± 2.5 mm) in adult females for the upper lip, and for the lower lip −3 to −4 mm (± 2 mm) in adult males and −3 to −3.5 mm (± 2 mm) in adult females. The age of adults in their group ranged between 16 and 20 years.

Coleman et al found that fuller lip positions were preferred for more extreme retrognathic and prognathic profiles. Czarnecki et al found that more lip protrusion was deemed acceptable for both male and female faces when either a large nose or a large chin was present. Foster found that diverse groups seemed to share a common esthetic standard for lip prominence, in most patients within 1-2 mm, that all groups were consistent in assigning fuller lips for younger ages, that all groups preferred at least 3 mm fuller lips for adult females; except orthodontists, who saw full lips at 1.4 mm, and all groups preferred adult male lips to be more behind the E-line than the original Ricketts ideal values, with adult females closer to, but still further behind the ideal values.

A number of previous studies have assessed sagittal lip prominence in relation to ethnic variability of the images and/or observers. Hall et al found that participants preferred African American sample profiles, with upper and lower lips that were more prominent, over white sample profiles. McKoy-White et al looked at lip protrusion and retrusion, resembling bimaxillary protrusion and retrusion, using manipulated photographs of 3 black female profiles. They found that white orthodontists preferred flatter profiles than the black women patients and that black women patients preferred fuller profiles than the black orthodontists. They also found subjective differences in profile attractiveness among different ethnic groups, subjective differences in profile attractiveness among orthodontists of different ethnic groups (white or African American), and contrary to previous research, that black women did not favor a flatter or more whiteprofile. Mejia-Maidl et al found that Mexican Americans preferred upper and lower lip positions to be less protrusive than white groups. Battle et al found that younger orthodontists favored more prominent lips in profile. They concluded that orthodontists working on various ethnic populations should be more conscious of using standardized profile analyses. Huang and Li assessed Chinese patients with bimaxillary protrusion and found that retraction of their lips relative to the E-line correlated with an improvement in attractiveness ratings.

Al Abdulwahhab et al found that Saudi observers generally preferred lips to be further behind the E-line than the Western standard. They also noted the observers’ greater tolerance for the lips to move away from rather than toward the E-line. Chong et al found that Chinese judges preferred a more retrusive profile and were more likely to rate prominent lips, particularly ahead of the E-line, as unacceptable, compared with the white judges. Hockley et al found that flatter profiles with less lip prominence than the esthetic norm were more often preferred in silhouettes than in photographs and concluded that using silhouettes to evaluate patient esthetics could influence clinicians or researchers to select profiles that are flatter than the established esthetic norm . The small number of raters (n = 15, all faculty and residents) in this investigation warrants a repeat of these potentially interesting results.

The principal aim of this investigation was to quantitatively evaluate the influence of lip prominence as represented by sagittal position in relation to the E-line on perceived attractiveness. The relationship between lip prominence and attractiveness was recorded to ascertain the range of normal variability in terms of observer acceptance and to determine the clinically significant threshold value or cutoff point beyond which lip position is perceived as unattractive and treatment is desired. The perceptions of patients, clinicians, and laypeople were compared for these different variables.

Material and methods

Ethical approval was granted by the National Research Ethics Service (REC no. 06/Q0806/46), United Kingdom.

Two-dimensional profile silhouettes are used routinely to assess the perception of facial attractiveness. , A profile silhouette image was created with computer software (Photoshop CS2, Adobe, San Jose, Calif). The image was manipulated using the same software to construct an ideal profile image with proportions and linear and angular soft-tissue measurements, , , on the basis of currently accepted criteria for an idealized white male profile, as previously described. The sagittal position of the lips of the idealized image (image BE, −6 mm measured as upper lip from E-line) was altered in 2-mm increments from −16 mm to 4 mm to represent variations of bilabial position and morphology from excessive prominence to excessive retrusion ( Fig 1 ).

Fig 1
The sagittal prominence of the lips of the idealized profile image was altered incrementally in relation to the E-line, creating a series of images. The 2-letter code assigned to each image and the distance of the lips to the E-line in millimeters shown in this figure are provided on each image for clarity; for data collection, the distance of the lips to the E-line was not on the images shown to observers, and the 2-letter code was located outside each image on the computer monitor background.

On the basis of the results of a pilot study and power calculation, 185 observers took part in the study, separated into 3 groups (pretreatment orthognathic patients, laypeople, and clinicians; Table I ) with the following selection criteria:

  • 1.

    Patients: pretreatment (only 1 consultation appointment); primary concern was facial appearance; no previous facial surgical treatment; no history of facial trauma; no severe psychological issues (on the basis of the patient interview by the lead investigator).

  • 2.

    Laypeople: no previous facial surgery, deformities, or history of facial trauma; selected randomly from a range of nonmedical backgrounds (eg, teachers, teaching assistants, parents of school children, police officers, firefighters).

  • 3.

    Clinicians: involved in the management of patients with facial deformities; included 19 maxillofacial surgeons and 16 orthodontists, with 1-16 years of experience in the clinical management of patients requiring orthognathic and facial reconstructive surgery.

Table I
Observer demographics
Observer group n Mean age (y) 95% CI Age range (y) Gender (% male) Ethnicity (% white)
Orthognathic patients 75 22 20-24 13-60 42 66
Laypeople 75 31 28-35 16-79 31 49
Clinicians 35 31 30-33 24-39 33 72

CI, Confidence interval.

Each observer was given a questionnaire and asked to provide the following information: (1) age, (2) gender, (3) ethnic origin (white or nonwhite), (4) self-rated attractiveness of facial appearance, and (5) self-rated importance of attractive facial appearance. An instruction sheet accompanied the questionnaire, asking the observers to rate each image in terms of facial attractiveness using the following rating scale: (1) extremely unattractive, (2) very unattractive, (3) slightly unattractive, (4) neither attractive nor unattractive, (5) slightly attractive, (6) very attractive, and (7) extremely attractive.

Observers were also asked whether they would consider treatment to correct the appearance if this was their facial appearance (yes or no).

The images were placed in random order into a PowerPoint presentation (Microsoft, Redmond, Wash). Each image was identified by a randomly assigned double letter in the top right corner of the screen (eg, BE and CF; Fig 2 ). A duplicate image assessed intraexaminer reliability (images DH and EG). Each observer sat undisturbed in the same room in front of the same computer and 17-in flat-screen monitor. The presentation and the images were created in such a way that each of the profile silhouette images, when viewed on the monitor, had the same dimensions as a normal human head, based on an average lower facial height, reducing the potential effect of the image size on observer perception. Each observer examined the images in the PowerPoint presentation by pressing the Page Down button on the keyboard in their own time. The Likert-type rating scale is largely accepted in the psychology literature as the most useful rating method. The 7-point Likert scale was used by each observer to rate each image in terms of attractiveness.

Jun 12, 2021 | Posted by in Orthodontics | Comments Off on Quantitative investigation of the esthetic impact of lip prominence in relation to the esthetic line
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