To evaluate the influence of vermilion height on the assessment of lip attractiveness by Japanese and Korean orthodontists and orthodontic patients.
Vermilion heights were modified by increasing or decreasing the vermilion height in 1.0-mm increments from −3.0 mm to 3.0 mm with reference to an average vermilion height. Participants ranged from 15 to 29 years of age and comprised 29 Japanese and 25 Korean orthodontists and 96 Japanese and 72 Korean orthodontic patients. They all rated the attractiveness of seven images with altered vermilion height using a visual analog scale.
Across the participant groups, there were significant differences in the median esthetic scores for the seven vermilion height levels tested. The Japanese and Korean raters assigned the highest scores to the average vermilion height and assigned the lowest scores to the +3-mm increased vermilion height. The ranges of vermilion height preferred by orthodontists were found to be within the ranges preferred by orthodontic patients when evaluating the preferences in lip esthetics by country.
We conclude that the −1-mm to +1-mm range for the average vermilion height is considered attractive for lips for both Japanese and Korean people.
Facial esthetics is of particular concern for both orthodontists and orthodontic patients. The face plays a key role in communication and interpersonal interaction.1 People with unattractive faces are considered less intelligent and are more likely to be isolated.2 Patients seek orthodontic treatment to obtain medical modification of unattractive dentofacial features.3 Because the lips and teeth are considered fundamental factors in facial appearance, contemporary orthodontics must consider the esthetic of the mouth by managing the dentition and soft tissues.4 Previous studies5–7 have been conducted using cephalograms in the lateral view to evaluate the esthetic features of the anteroposterior lip positions. Because patients tend to judge their own facial esthetics in the mirror, studies investigating lip esthetics in the frontal view are warranted.
Traditionally, larger and more prominent lips (in comparison to that of the average Caucasian lip) have offered the preferred lip appearance.8 In fact, Peck and Peck9 demonstrated that attractive Caucasians have larger lips than the normal. Sforza et al.10 also suggested that attractive adolescents have larger and more prominent lips than the normal. A further study suggests that facial preference might be related to age-related features that signal youthfulness and fertility.9 McNamara et al.11 suggested that vermilion height plays one of the most important roles in determining smile esthetics. They11 also showed that the vertical thickness of the upper and lower lips is an esthetic determinant for laypersons. Thus, vertical lip thickness appears to be an important factor in the determination of attractiveness of mouth appearance. However, there has not been ample evidence in the literature with regard to the extent to which orthodontists and orthodontic patients consider vermilion height when assessing attractiveness in lips.
Demographic, cultural, and ethnic background may affect a layperson's esthetic perception.12–14 Historically, Japanese and Korean people occupy the same racial group and have similar cultural backgrounds. At the current moment, these two groups frequently travel and are exposed to international mass media. Therefore, the perceptions of facial beauty in these populations may be very similar and may converge with a more internationally based esthetic. Given the data concerning attractiveness in the literature, this study aims to evaluate the influence of vermilion height on lip esthetics as assessed by Japanese and Korean orthodontists as well as orthodontic patients.
It is very important to evaluate the perceptions of the facial esthetics in laypeople or orthodontic patients when the orthodontic treatment objective is determined. In general, laypersons are more forgiving than are dental professionals in the evaluations of dental esthetics.15 In our previous study16 investigating the attractive amounts of buccal corridor, both orthodontists and orthodontic patients showed similar tendencies in their preferences. To date, there has been no report that has compared preferences for vermilion height between orthodontists and orthodontic patients.
The overall purpose of this study was to identify the threshold at which vermilion height begins to decrease lip esthetics at a resting position among Japanese and Korean orthodontists and orthodontic patients. The hypotheses were (1) that the vermilion height would affect the assessment of lip esthetics, (2) that there would be no significant differences in the assessment of lip esthetics between Japanese and Korean people, (3) that there would be no significant differences in the assessment of lip esthetics between orthodontists and orthodontic patients, and (4) that a distinct threshold of preference would exist when the effects of vermilion height on lip esthetics at rest position are evaluated.
MATERIALS AND METHODS
This study was performed in accordance with the guidelines of the Helsinki Declaration revised in Seoul (2008). The research protocol was approved by the Kyushu University Institutional Review Board for Clinical Research.
A sample size calculation was undertaken using nQuery Adviser (Version 6.01, Statistical Solutions, Cork, Ireland). Based on our pilot study, the effect size was estimated at 1.01. On the basis of a significance level of α = .05, the sample size was calculated to achieve 80% power. The sample size calculation showed that 19 subjects were needed for each group.
Construction of a Series of Images
One female extraoral photograph that displayed esthetic lips at a resting position with an average vermilion height was obtained from a volunteer. We defined the vermilion height as the length between the superior vermilion border and the inferior vermilion border. For the upper lip, we set the average vermilion heights as 7.8 mm and 9.5 mm at the labrale superius and either side of crista philtri, respectively. For the lower lip, we set the average vermilion height as 12.2 mm at the labrale inferius.17 This image was modified using Adobe Photoshop CS4 (San Jose, Calif) to create an accurate average vermilion height and bilaterally symmetrical lips. Vermilion heights were modified by increasing or decreasing the vermilion height in 1.0-mm increments from −3.0 mm to 3.0 mm with reference to the average vermilion height. Seven images were arranged at random and displayed on size A-4 paper (Figure 1).
The raters, aged 15 to 29 years, comprised 29 Japanese orthodontists (10 males, 19 females; 31.5 ± 4.7 years of age), 96 Japanese orthodontic patients (36 males, 60 females; 21.5 ± 3.8 years of age; from Kyushu University Hospital in Fukuoka, Japan), 25 Korean orthodontists (12 males, 13 females; 27.9 ± 2.3 years of age), and 72 Korean orthodontic patients (33 males, 39 females; 22.2 ± 3.2 years of age; from Pusan National University Dental Hospital in Pusan, Korea). Determination of the subjective esthetic value of each vermilion height was accomplished using a visual analog scale (VAS). This rating scale was designed to minimize constraints and maximize the freedom to express a personal preference. The VAS was 50 mm long, and raters used their own values to rank each vermilion height from “least attractive” to “most attractive.” An esthetic score was obtained by multiplying the distance between the least attractive (zero) and the hash mark by two. More specifically, the esthetic score was distributed from 0 to 100, 0 being the minimum and 100 the maximum esthetic value.
Ten randomly selected raters from each of the Japanese and Korean orthodontist and orthodontic patient groups were asked to evaluate seven images twice at least 2 weeks later to determine reliability. Intraclass correlation coefficients (ICCs) were used to detect the intrarater agreement. High levels of reliability were found, as all ICC values were greater than or equal to 0.7.
Statistical Analysis of the Data
To compare the distributions of the median scores between the male and female raters for each of the rater groups, the Mann-Whitney U-test was conducted. Differences in the median esthetic scores for the seven vermilion heights were analyzed using the Kruskal-Wallis test. The minimum level of statistical significance was set at P < .05.
The VAS has been used in pain research, and, in general, a minimum clinically significant difference ranges from 9% to 13% of the VAS scale.18–20 Parekh et al.21 applied a 15% VAS difference as a clinically significant difference to differentiate smile esthetics. We also used a 15% difference in the esthetic score to determine clinical significance in the evaluation of lip esthetics.
No significant gender differences in judging the effects of vermilion heights on lip attractiveness were observed for either the Japanese or Korean orthodontists. Therefore, the data from both the male and the female Japanese or Korean orthodontists were pooled for the following analysis. The median values and ranges of the esthetic scores for each vermilion height for the Japanese and Korean orthodontists are shown in Table 1 and in Figure 2A and B. The Kruskal-Wallis test showed that there were significant differences in the median esthetic scores for the seven levels for both the Japanese and Korean orthodontists (P < .0001). For both the Japanese and Korean orthodontists, the median esthetic scores increased gradually for the −3-mm to 0-mm vermilion heights and then decreased for the 0-mm to +3-mm vermilion heights. We found clinically significant differences in the esthetic scores for vermilion heights between −3 mm and −1 mm and in those for vermilion heights between +1 mm and +3 mm, with the exception of the scores for the −3-mm and −2-mm heights rated by the Korean orthodontists. Moreover, no clinically significant difference was observed in the median esthetic score between the Japanese and Korean orthodontists for each level of vermilion height.
There were significant differences in judging the effects of vermilion height on lip attractiveness between the male and female Japanese or Korean orthodontic patients. The median values and ranges of the esthetic scores for each level of vermilion height for the Japanese and Korean orthodontic male patients are shown in Table 1 and Figure 3A and B. The Kruskal-Wallis test showed that there were significant differences in the median esthetic scores given to the seven levels by both the Japanese and Korean male orthodontic patients (P < .0001). For both the Japanese and Korean male orthodontic patients, the median esthetic scores increased gradually for vermilion heights from −3 mm to 0 mm and then decreased for heights from 0 mm to +3 mm. In particular, the score decreased in a clinically significant manner for vermilion heights from 0 mm to +1 mm and from +2 mm to +3 mm. In addition, we found clinically significant differences in the esthetic scores given to the −1-mm and 0-mm vermilion heights for the Japanese male orthodontic patients. The Japanese male orthodontic patients assigned higher scores to the −3-mm vermilion height than were given by the Korean male orthodontic patients, and this difference was clinically significant.
The median values and ranges of the esthetic scores given to each vermilion height by the Japanese and Korean orthodontic female patients are shown in Table 1 and in Figure 4A and B. The Kruskal-Wallis test showed that there were significant differences in the median esthetic scores given to the seven vermilion height levels by both the Japanese and Korean female orthodontic patients (P < .0001). For both the Japanese and Korean female orthodontic patients, the median esthetic scores increased gradually for vermilion heights from −3 mm to 0 mm and then decreased between the 0-mm to +3-mm vermilion height levels. In particular, clinically significant increases in the esthetic score were observed between the −3-mm and −2-mm levels and between the −1-mm and 0-mm levels. In addition, the score was also found to decrease between the +2-mm and +3-mm vermilion height levels. We found clinically significant differences in the esthetic scores between the 0-mm and +1-mm vermilion heights only in the data from the Japanese female orthodontic patients, while such differences for vermilion heights between +1 mm and +2 mm were found only in the data from the Korean female orthodontic patients. The Korean female orthodontic patients assigned higher esthetic scores for the +1-mm vermilion height level than were given by the Japanese female orthodontic patients, and this difference was clinically significant.
The present report is the first study to evaluate the effect of vermilion height on lip esthetics. The main finding of our study was that the Japanese and Korean raters had a common preference in the evaluation of vermilion height (ie, they assigned the highest scores to the average vermilion height and assigned the lowest scores to the +3-mm increased vermilion height). These findings suggest that orthodontists and orthodontic patients share similar preferences regarding lip esthetics at the rest position. Generally, the treatment objectives for orthodontic treatment lie within the average range when they do not conflict with physiological function or esthetic features. Our results suggest that the average vermilion height should be the goal of orthodontic treatments with respect to facial attractiveness. In a previous study,22 we demonstrated that Japanese and Korean adults preferred a retruded profile, although their profiles have historically been characterized by more bimaxillary protrusion facial features. Thus, the treatment modality of extracting four premolars has been chosen to straighten the facial profile and make lip seal easy. We also showed that as a result of the posterior movement of anterior teeth, this treatment significantly decreased the vermilion height from the increased height that results from labially inclined anterior teeth toward the average vermilion height.23 Considering these results in conjunction with those obtained in the present study, extraction treatments not only improve facial profiles but could also decrease vermilion height toward the attractive average value in the frontal view.
Interestingly, the Korean female orthodontic patients tended to assign higher scores to the +1-mm increased vermilion height compared with the corresponding Japanese female raters. Peck and Peck9 suggested that the esthetically attractive White face demonstrated larger lips than normal. This preference is thought to be linked to youthfulness and fertility and suggests a strong evolutionary influence on attractiveness.4,24 The high acceptability of the +1-mm increased vermilion height in the Korean female raters might be due to this preference tendency.
Assuming that an unattractive vermilion height is reflected by esthetic scores of 0 to 50 and that an attractive vermilion height is reflected by scores from 51 to 100, the Japanese and Korean orthodontists and Korean female orthodontic patients considered vermilion heights from −1 mm to +1 mm to be attractive. On the other hand, Japanese female orthodontic patients and Korean male orthodontic patients considered vermilion height from −2 mm to +2 mm to be attractive. It is interesting to note that the Japanese male orthodontic patients gave higher scores to the lower vermilion heights. These results suggest that, in general, laypersons would have a broader tolerance for vermilion height changes than would dental professionals.15 However, Korean female raters had narrow and specific ranges for their preferences in vermilion height evaluations. Considering that the relatively narrow range of vermilion heights preferred by the orthodontists is within the relatively broad tolerances of the orthodontic patients in both countries, it would be prudent for clinicians to set a goal to around-average vermilion height in determining treatment plans.
In the evaluation of esthetic vermilion heights there are a few limitations in the methodology. Using a computer to alter vermilion heights might not be a perfect method because there is a threshold level that a digital alteration must exceed for the viewer to detect it. In those cases, there would be some detraction from lip esthetics. However, using the same image and modifying only one variable, we could focus on evaluating the effects of the altered vermilion heights on lip esthetics. Another limitation is that since the sample sizes of orthodontists in both countries were relatively small, the results must be interpreted with caution. Although it was still useful to analyze the orthodontist groups to evaluate whether there were any interesting trends, the groups comprised convenience samples, and some bias may have been introduced. Additional research evaluating the perception of vermilion height on a smiling face appears to be warranted.
Vermilion height affected the assessment of lip esthetics.
Overall, the Japanese and Korean raters had common preferences in their evaluation of vermilion height (ie, they assigned the highest scores to the average vermilion height and assigned the lowest scores to the +3-mm increased vermilion height).
The ranges of vermilion height preferred by orthodontists were within those preferred by orthodontic patients in both countries.
A distinct threshold existed when the effect of vermilion height on lip esthetics was evaluated.
We propose that the range of −1 mm to +1 mm, with reference to the average vermilion height, is the range over which Japanese and Korean people find lips attractive.
We thank Drs Ze'ev Davidovitch and Amy L. Counts for their valuable help with this manuscript.