Recognition of the Asymmetrical Smile: A Comparison of Orthodontists, Oral and Maxillofacial Surgeons, and Laypersons

CRANIOMAXILLOFACIAL DEFORMITIES/SLEEP DISORDERS/COSMETIC SURGERY

Recognition of the Asymmetrical Smile: A Comparison of Orthodontists, Oral and Maxillofacial Surgeons, and Laypersons Soheil Rostami, MS, DDS,* Balraj Kang, DDS,y Eser Tufekci, DDS, MS, PhD, MSHA,z Spiro C. Stilianoudakis, BS, MA,x Caroline K. Carrico, PhD,k and Daniel M. Laskin, DDS, MS{ Purpose:

Studies have shown that an asymmetrical smile is a relatively common problem. Yet, many patients are unaware of having this condition. Because having an asymmetrical smile can affect the final esthetic result of orthodontic therapy or orthognathic surgery, such patients need to be aware of the problem. The purpose of this study was to determine what amount of smile asymmetry is clinically evident to orthodontists, oral and maxillofacial surgeons (OMSs), and the lay public.

Materials and Methods:

A total of 56 OMSs, 117 orthodontists, and 123 laypersons participated in the study. They were asked to view a randomly arranged series of computer-generated male and female facial photographs with the smile symmetrical or altered in 0.5-mm increments from 1 to 4 mm and to indicate whether the person had an asymmetrical smile.

Results:

The OMSs and orthodontists were able to recognize relatively smaller amounts of asymmetry than the laypersons (2 mm vs 3 to 3.5 mm).

Conclusions: Although the clinicians performed better than the laypersons, both groups were able to recognize relatively small amounts of asymmetry. Because such a condition is generally not correctable and can affect the esthetic result, patients undergoing orthodontic therapy or orthognathic surgery need to be made aware of the situation before treatment. Ó 2019 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-9, 2019

One of the most important components of facial attractiveness is an esthetic smile. Studies have shown that an esthetic smile can affect not only social status and quality of life but also the perception of one’s personal attributes such as intelligence, popularity, and academic success.1-3 According to a recent survey by the American Academy of Cosmetic Dentistry,4

89% of patients seek dental treatment to improve physical attractiveness and self-esteem.3-6 These patients have a heightened awareness of their facial appearance and expect esthetic improvements as a result of their treatment.6,7 In orthodontics, although treatment is mainly based on dental esthetics, variables such as facial midline,

Received from Virginia Commonwealth University, Richmond, VA.

Address correspondence and reprint requests to Dr Laskin:

*Resident, Department of Oral and Maxillofacial Surgery.

Department of Oral and Maxillofacial Surgery, Virginia Common-

yResident, Department of Oral and Maxillofacial Surgery.

wealth University School of Dentistry, 521 N 11th St, Richmond,

zProfessor, Department of Orthodontics, School of Dentistry.

VA 23298-0566; e-mail: [email protected]

xGraduate Student, Department of Biostatistics, School of

Received July 22 2019

Medicine. kAssistant Professor, Department of Oral Health and Community

Ó 2019 American Association of Oral and Maxillofacial Surgeons

Outreach, School of Dentistry.

0278-2391/19/31048-1

Accepted August 27 2019

{Professor and Chairman Emeritus, Department of Oral and

https://doi.org/10.1016/j.joms.2019.08.023

Maxillofacial Surgery, School of Dentistry. Conflict of Interest Disclosures: None of the authors have any relevant financial relationship(s) with a commercial interest.

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smile line, and buccal corridors are also important factors.7,8 These components, first evaluated by Hulsey8 in 1970, were found to considerably affect the smile esthetics. Furthermore, asymmetrical smiles were reported to negatively affect smile attractiveness. However, to date, there is limited information on smile asymmetry in the literature. In 2001, a study by Benson and Laskin9 showed that about 9% of 195 dental students aged between 21 and 44 years had an asymmetrical smile due to canting of the upper lip. However, only 2 of the stu-

dents were aware of the asymmetry. A subsequent study in 2018 found that 22% of 54 volunteers showed a 2.5-mm or greater difference between the right- and left-sided commissures of the lip when smiling.10 Because an asymmetrical smile is not correctable, it is essential that it be recognized in patients considering orthodontics and/or orthognathic surgery so that they can be informed of its possible effect on the final esthetic result. In this regard, it is important to understand what degree of asymmetry is clinically

FIGURE 1. Original photographs (left) and construction of symmetrical images (right) of female volunteer (A) and male volunteer (B). Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

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FIGURE 2. Horizontal and vertical lines identifying right-sided lip commissure (RLC). The vertical line was used to prevent lengthening or shortening of the lip in a horizontal direction, and the horizontal line was used as a reference point for alteration of the smile in a downward vertical direction. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

evident. Therefore, the purpose of this study was to determine the minimal amount of asymmetry detectable by orthodontists, oral and maxillofacial surgeons (OMSs), and laypersons.

Materials and Methods Ethical approval for this survey study was obtained from the Institutional Review Board at Virginia Commonwealth University (HM20011824). One female dental student and one male dental student with well-balanced facial proportions and esthetic smiles volunteered to participate, and their images were used to construct the survey questionnaire. Frontal pictures were taken with the volunteers 2 m from the camera. They were asked to smile naturally in centric occlusion. Each volunteer held a standard Westcott ruler (Acme United, Fairfield, CT) parallel to the face and aligned with the lip. This method served to calibrate the measurements when the images were subsequently altered to create asymmetrical smiles in Adobe Photoshop CC (Adobe Systems, San Jose, CA). Changes in the images were made using the healing brush tool. The maxillary central incisors were identified as the midline landmark, and a vertical line was placed between these teeth to create a mirror image. These symmetrical images were used as the control (Fig 1). Next, 7 additional male and female images with varying amounts of lip asymmetry were created using the aforementioned symmetrical images. For the purpose of standardization, the right-sided lip commissure was chosen as the point to be altered in each image. Vertical and horizontal lines were used to mark the right-sided lip commissure (Fig 2). The vertical line helped to prevent lengthening or shortening of the lip in the horizontal plane. The horizontal line served

as a reference point to shift the lip down in a vertical direction in 0.5-mm increments (1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 mm) to create the asymmetry (Fig 3). Three parallel surveys, each containing the same 16 smiling photographs (1 control view and 7 experimental views of both the male volunteer and female volunteer), were distributed to the OMSs, orthodontists, and laypersons. The order of presentation of each set of images was randomized using a computer-generated sequence. Male images were provided first in the following order: 3 mm, 2.5 mm, symmetrical, 4 mm, 2 mm, 3.5 mm, 1.5 mm, and 1 mm. These were followed by the female images in the following order: 3 mm, 1.5 mm, 2 mm, 4 mm, 2.5 mm, symmetrical, 1 mm, and 3.5 mm. A total of 290 members randomly selected from 6 membership districts of the American Association of Oral and Maxillofacial Surgeons received individual emails through the REDCap survey system and were asked to complete the survey using a unique link. Nineteen emails were not deliverable and subsequently were removed from the response-rate calculations. For the orthodontists, the American Academy of Orthodontics Partners in Research submitted the survey to 2,197 of its members randomly chosen from its directory. These individuals received a mass email with 1 generic REDCap link to the survey. The laypersons consisted of students in the Virginia Commonwealth University Schools of Medicine and Pharmacy. We invited 720 medical students and 560 pharmacy students to participate. They were sent the invitation to participate in the survey via email using the 4 class mailing lists for each school. These emails also included a generic REDCap link to the survey. First, respondents in all groups were asked to indicate their gender, age, and years in practice if applicable or field of study and year in school if they were laypersons. Respondents in the layperson group also were asked to confirm if they had ever undergone orthodontic treatment or orthognathic surgery. If they selected yes, the survey ended for these individuals. Then, the respondents in all groups were asked to view the photographs and to indicate whether the individual in each image had an asymmetrical smile (yes or no answer). Once the question was answered, the respondent could not return to the photograph and alter the answer. STATISTICAL ANALYSIS

The c2 test for equality of proportions was used to determine if there was a significant difference in correct responses when respondents were presented with the male and female images with no smile asymmetry. A total of 4 tests, stratified by respondent group and gender of the image, were performed: 1) male

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RECOGNITION OF ASYMMETRICAL SMILE

FIGURE 3. Images of female (A) and male (B) volunteers used in the survey questionnaire presented in the original order. The symmetrical image is labeled 0.0 mm, and the altered images are labeled by the amount of smile asymmetry ranging from 1.0 to 4.0 mm. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

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image rated by OMSs versus orthodontists, 2) female image rated by OMSs versus orthodontists, 3) male image rated by medical students versus pharmacy students, and 4) female image rated by medical students versus pharmacy students. On the basis of the findings, the inter-respondent groups, comprising OMSs plus orthodontists and medical students plus pharmacy students, were then combined into 2 groups labeled ‘‘clinicians’’ and ‘‘laypersons,’’ respectively. Two additional c2 tests for equality of proportions were used to determine if there was a difference between these 2 groups in correctly identifying the male and female images with no smiling asymmetry. The percentage of correct responses between clinicians and laypersons to the various images with increasing levels of asymmetry was determined using generalized estimating equations, with logit links. Autoregressive (lag1) correlation structures were assumed to account for correlations among answers from the same respondent for adjacent levels of asymmetry. These models were first used to test for differences between clinicians (orthodontists vs OMSs) and between laypersons (pharmacy students vs medical students). On the basis of these results, subsequent models were fit and Tukey post hoc tests were used to determine if there were differences between the respondent types at each level of asymmetry. These models also were used to determine if there was a ‘‘plateau’’ point for each respondent type at which the percentage responding correctly no longer increased with an increased degree of asymmetry. The a level of significance was set at .05. All statistical analyses were performed using the R program (version 3.5.1; R Foundation for Statistical Computing, Vienna, Austria).

Table 1. DEMOGRAPHIC CHARACTERISTICS OF 173 CLINICIANS INCLUDED IN STUDY

Characteristic Gender Female Male Specialty Oral and maxillofacial surgery Orthodontics Years in practice 0-5 yr 6-10 yr 11-15 yr 16-20 yr $21 yr

n (%) (N = 173)

59 (34) 114 (66) 56 (32)

Table 2. DEMOGRAPHIC CHARACTERISTICS OF 123 LAYPERSONS INCLUDED IN STUDY

Characteristic

n (%) (N = 123)

Gender Female Male Type of student Medical Pharmacy Year First Second Third Fourth Age group 21-22 yr 23-24 yr 25-26 yr >26 yr

95 (77) 28 (23) 45 (37) 78 (63) 42 (34) 25 (20) 31 (25) 25 (21) 17 (14) 42 (34) 37 (30) 27 (22)

Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

Results A total of 65 OMSs responded to the survey, but after removal of partial responses, 56 were included in the final analysis. This constitutes a 21% response rate (56 of 271 OMSs). Responses were received from 117 of the 2,197 orthodontists (5%), 45 of the 720 medical students (6%), and 78 of the 560 pharmacy students (14%) (Tables 1 and 2). Most clinicians identified themselves as male individuals and were in practice for more than 21 years. Most laypersons identified themselves as female individuals. They ranged in age from 21 years to more than 26 years. The percentage of correct responses between clinicians and laypersons for the images with no asymmetry are given in Table 3. When participants were presented with a male image without smile asymmetry, the percentage of correct response was

Table 3. BASELINE PERCENTAGE OF CORRECT RESPONSES BETWEEN CLINICIANS AND LAYPERSONS WHEN PRESENTED IMAGE WITH NO SMILE ASYMMETRY STRATIFIED BY IMAGE GENDER

Image

Class

% of Correct Responses

Male

Clinician Layperson Clinician Layperson

97.1 92.7 98.3 91.9

117 (68) 29 (17) 31 (18) 24 (14) 13 (8) 76 (43)

Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

Female

P Value .136 .0183

Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

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FIGURE 4. Line plots illustrating the difference in the percentage of correct responses between oral and maxillofacial surgeons and orthodontists at each level of smile asymmetry and across both genders. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

97.1% and 92.7% for clinicians and laypersons, respectively (P = .1361). However, when a female image without smile asymmetry was presented, the disparity in the percentage of correct response was slightly wider, with 98.3% and 91.9% for clinicians and laypersons, respectively. These baseline percentages were significantly different (P = .0183). These results

validated the need to perform separate analyses specific to the gender of the image presented. Recognition of an asymmetrical smile was not significantly different between orthodontists and OMSs for any degree of smile asymmetry (P > .05 for all levels, Fig 4). Diagnostic accuracy also was found not to be significantly different between medical and pharmacy

FIGURE 5. Line plots illustrating the difference in the percentage of correct responses between the 2 groups of laypersons at each level of smile asymmetry and across both genders. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

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Table 4. POST HOC PAIR-WISE COMPARISON TESTS ASSESSING DIFFERENCE IN PERCENTAGE OF CORRECT RESPONSES BETWEEN CLINICIANS AND LAYPERSONS FOR EACH LEVEL OF SMILE ASYMMETRY ACROSS IMAGE GENDER

Image Gender Male

Asymmetry, mm 1 1.5 2 2.5 3 3.5 4

Female

1 1.5 2 2.5 3 3.5 4

Respondent Class

Estimated % of Correct Responses

95% CI of %

SE

Lower

Upper

OR

P Value

C LP C LP C LP C LP C LP C LP C LP C LP C LP C LP C LP C LP C LP C LP

4.0 7.3 46.2 22.8 86.7 63.4 93.1 72.4 90.8 73.2 98.8 89.4 98.8 91.1 22.5 13.0 52.0 21.1 86.7 61.8 89.0 70.7 94.2 86.2 97.1 93.5 98.3 90.2

1.5 2.3 3.7 3.7 2.5 4.3 1.9 4.0 2.2 4.0 0.8 2.7 0.8 2.5 3.1 3.0 3.8 3.6 2.5 4.3 2.3 4.1 1.7 3.1 1.2 2.2 0.9 2.6

1.9 3.9 38.9 16.2 80.8 54.6 88.2 63.8 85.4 64.7 95.5 82.6 95.5 84.6 14.6 6.4 41.1 12.4 77.3 48.5 80.0 57.6 86.3 74.5 90.0 83.2 91.2 79.3

8.2 13.5 53.7 31.0 91.0 71.4 96.0 79.5 94.3 80.3 99.7 93.8 99.7 95.0 33.1 24.6 62.8 33.7 92.6 73.5 94.3 81.1 97.7 93.0 99.2 97.7 99.7 95.7

0.53

.226

2.92

<.0001

3.76

<.0001

5.13

<.0001

3.6

<.0001

10.1

.003

8.40

.006

1.95

.039

4.05

<.0001

4.03

<.0001

3.35

<.0001

2.61

.021

2.34

.145

6.13

.006

Abbreviations: C, clinician; CI, confidence interval; LP, layperson; OR, odds ratio; SE, standard error. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

students in the layperson group (P > .05 for all levels, Fig 5). Therefore, the 2 clinician groups were combined and the 2 student groups were combined for all subsequent analyses. Results from the model to assess the percentage of correct responses of clinicians and laypersons at increasing levels of smile asymmetry are given in Table 4 and Figure 6. When the male images were presented, the lowest percentage of correct responses was at the 1-mm level of asymmetry for both clinicians and laypersons. At this level, the percentage of correct responses was not significantly different between the 2 respondent groups (P = .2260). However, there was a disparity in the percentage of correct responses at increasing levels of asymmetry. After 1 mm, clinicians were found to have a significantly greater percentage of correct responses than laypersons

(Fig 6). The greatest difference was at the 2-mm level of smile asymmetry (87% vs 63%, P < .0001). When presented with the female images, clinicians exhibited a significantly greater percentage of correct responses at all levels of smile asymmetry except 3.5 mm, for which the percentage of correct responses of the layperson group was not significantly different from that of the clinicians (97% vs 93%, P = .1452). The percentages of correct responses at consecutive levels of smile asymmetry between clinicians and laypersons, within the gender of the image presented, also were compared to detect a plateau point (Table 5). For the male images, clinicians exhibited significantly different rates of correct responses between the 1- and 1.5-mm levels and between the 1.5- and 2-mm levels of smile asymmetry, after which they plateaued. For the male images,

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RECOGNITION OF ASYMMETRICAL SMILE

FIGURE 6. Line plots illustrating the difference in the percentage of correct responses between clinicians and laypersons at each level of smile asymmetry and across both genders. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

clinicians could correctly identify asymmetry above 2 mm with an average accuracy of at least 87%. The layperson group, on the other hand, exhibited an additional significant increase in the percentage of correct responses from the 3- to 3.5-mm level of asymmetry. This finding indicated that the laypersons needed additional amounts of asymmetry to comfortably identify a male image smile as being asymmetrical—although still at a lower level of accuracy than the clinicians. Furthermore, when presented with the female images, clinicians exhibited similar profiles of correct responses as with the male images. A plateau in the percentage of correct responses was again seen after the 2-mm level of asymmetry, with clinicians detecting asymmetry with an average of 87% accuracy or greater. In contrast, laypersons evaluating female images exhibited a significant increase in the percentage of correct responses only from 1.5 to 2 mm of asymmetry, after which none of the increases were statistically significant.

Discussion As might be expected, the orthodontists and OMSs were generally better able to recognize an asymmetrical smile than the layperson group. The greatest accuracy began at 2 mm for the clinicians but not until between 3 and 3.5 mm for the layperson group. Although both groups were equally accurate in recognizing the symmetrical male image, the laypersons were less able to recognize the symmetrical female image. The same

was true for the images with an asymmetrical smile. This finding might be a reflection of the ability of the clinicians to more quickly learn how to identify an asymmetry or lack thereof. In a relatively similar study, laypersons were less accurate than orthodontists in detecting transverse chin asymmetry in female individuals than in male individuals, and the authors attributed this finding to the order in which the images were presented (female-male) providing a learning curve.11 The results of our study show that both clinicians and laypersons are able to recognize very small amounts of smile asymmetry, but they do not answer the question of how much asymmetry is considered unattractive. This may vary in different individuals. Moreover, because the condition is generally not correctable, it can adversely affect a patient’s satisfaction with the results of orthodontic treatment or orthognathic surgery. Thus, it is important that, before treatment, clinicians determine if an asymmetrical smile is present and if the patient is aware of the condition. Although the subsequent treatment will not make the condition worse—and there may even be some general improvement—such a discussion will give the patient more realistic expectations. A limitation of this study was the relatively low response rate. However, although low, the response rate was typical for an online-based survey. In addition, the demographic characteristics were closely representative of the populations surveyed, albeit with a slightly increased presence of women in the layperson population. Another limitation of the study relates to the

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Table 5. ESTIMATED ORS FOR CORRECT RESPONSE BETWEEN CONSECUTIVE SMILE ASYMMETRIES FOR BOTH CLINICIANS AND LAYPERSONS ACROSS IMAGE GENDER

Image Gender

Respondent Class

Male

Clinician

Consecutive Asymmetry, mm

OR

P Value

1 vs 1.5 1.5 vs 2 2 vs 2.5 2.5 vs 3 3 vs 3.5 3.5 vs 4 1 vs 1.5 1.5 vs 2 2 vs 2.5 2.5 vs 3 3 vs 3.5 3.5 vs 4 1 vs 1.5 1.5 vs 2 2 vs 2.5 2.5 vs 3 3 vs 3.5 3.5 vs 4 1 vs 1.5 1.5 vs 2 2 vs 2.5 2.5 vs 3 3 vs 3.5 3.5 vs 4

0.05 0.13 0.49 1.37 0.11 1.00 0.27 0.17 0.66 0.96 0.32 0.83 0.27 0.17 0.80 0.50 0.49 0.59 0.56 0.17 0.67 0.39 0.43 1.55

<.0001 <.0001 .488 .999 .135 >.999 .006 <.0001 .772 >.999 .010 .999 <.0001 <.0001 >.999 .737 .971 >.999 .832 <.0001 .841 .052 .268 .993

Layperson

Female

Clinician

Layperson

Abbreviation: OR, odds ratio. Rostami et al. Recognition of Asymmetrical Smile. J Oral Maxillofac Surg 2019.

understanding of the significance of the lesser ability of laypersons to recognize an asymmetry in female individuals. Future studies could benefit not only from randomizing the order of the asymmetries within the gender of the image but also from randomizing the entire set of images so that male and female images are intermingled. Interspersing the male and female images may better test the true ability to detect an asymmetry and less

the result of training the eye to detect such a change. Finally, because this study shows the ability of laypersons to detect an asymmetry as small as 3 mm at a relatively high rate (approximately 75% accuracy), subsequent studies should be conducted to determine the amount of asymmetry that has an impact on patients’ perceived attractiveness. The ability to recognize an asymmetrical smile was similar for OMSs and orthodontists, but both groups were better able than laypersons to recognize an asymmetrical smile. However, because laypersons are still able to recognize a relatively small amount of smile asymmetry and the condition is generally not correctable, this situation needs to be discussed with patients before orthodontic treatment or orthognathic surgery.

References 1. Shaw WC: The influence of children’s dentofacial appearance on their social attractiveness as judged by peers and lay adults. Am J Orthod 79:399, 1981 2. Kiyak HA: Does orthodontic treatment affect patients’ quality of life? J Dent Educ 72:886, 2008 3. Henson ST, Lindauer SJ, Gardner WG, et al: Influence of dental esthetics on social perceptions of adolescents judged by peers. Am J Orthod Dentofacial Orthop 140:389, 2011 4. American Academy of Cosmetic Dentistry. State of the industry. Survey 2013. Available at: http://aacd.com. Accessed July 9, 2019 5. Langlois JH, Kalakanas L, Rubenstein AJ, et al: Maxims or myths of beauty? A meta-analytic and theoretical review. Psychol Bull 126:390, 2000 6. Pithon MM, Nascimento CC, Barbosa GC, Coqueiro RS: Do dental esthetics have any influence on finding a job? Am J Orthod Dentofacial Orthop 146:423, 2014 7. Springer NC, Chang C, Fields HW, et al: Smile esthetics from the layperson’s perspective. Am J Orthod Dentofacial Orthop 139: 91, 2011 8. Hulsey CM: An esthetic evaluation of lip-teeth relationships present in the smile. Am J Orthod 57:132, 1970 9. Benson KJ, Laskin DM: Upper lip asymmetry in adults during smiling. J Oral Maxillofac Surg 59:396, 2001 10. Mathis A, Laskin DM, Tufekci E, et al: Upper lip asymmetry during smiling: An analysis using three-dimensional images. Turk J Orthod 31:32, 2018 11. Jarosz KF, Bosio JA, Bloomstein R, et al: Perceptions of chin asymmetries among dental professionals and laypersons. Am J Orthod Dentofacial Orthop 154:201, 2018