Maxillary anterior crowding (MxAC) has been considered to be an esthetically favorable characteristic of young women in Japan. It has been hypothesized that laypeople and orthodontists have different esthetic preferences; however, to date, this has not been investigated in detail. Therefore, the present study compared the facial attractiveness of women with MxAC and the interpretation of MxAC among orthodontists and laypeople with and without orthodontic treatment experience in Japan.
Thirty-eight orthodontists, 42 laypeople with orthodontics (patients), and 43 laypeople without orthodontics (laypeople) evaluated the attractiveness of resting and smiling frontal images of 12 women with MxAC (MxAC models; mean age, 21.7 ± 2.6 years) and 12 women with normal occlusion (normal models; mean age, 20.1 ± 0.7 years) using a visual analog scale. In addition, they responded to a questionnaire that asked them to select the terms most closely associated with MxAC. All evaluators and models were Japanese.
For all evaluator groups, the facial attractiveness of the MxAC models was significantly lower than that of the normal models for both the resting and smiling images. For MxAC models, orthodontists evaluated resting images more attractive than smiling images, whereas laypeople evaluated smiling images more attractive than resting images. Significantly more patients and laypeople than orthodontists selected “cute” as the term most closely associated with MxAC ( P <0.05).
The orthodontists, patients, and laypeople showed a different tendency in their facial attractiveness preferences. Regardless of their orthodontic experience, the laypeople showed more positive interpretations of MxAC than orthodontists. This finding seems to be influenced by Japanese culture, which values irregularity in nature as one form of beauty.
In Japan, maxillary anterior crowding (MxAC) is often preferred by laypeople.
Orthodontists critically evaluated the facial attractiveness of women with MxAC.
Patients and laypeople selected “cute” as the associated word with MxAC.
Orthodontists selected “crooked teeth” and “unclean” associated with MxAC.
To establish an appropriate patient-doctor relationship for achieving a successful and satisfied outcome of orthodontic treatment, it is essential for the orthodontist to understand the patient’s preferences regarding dental and facial attractiveness. Maxillary anterior crowding (MxAC) is typically characterized as combined facial (often described as labial, buccal, or labiobuccal) displacement of the maxillary canines and palatal displacement of the maxillary lateral incisors. Possibly related to caries and periodontal disease caused by poor oral hygiene and increased risks for temporomandibular joint disorders, MxAC is an important factor not only esthetically but also functionally. MxAC is one of the chief concerns of young orthodontic patients regarding the dental appearance when smiling and is commonly derided as “fangs” or “snaggleteeth” in the United States. In contrast, in Japan, this malocclusion is commonly called Yaeba , which literally means the presence of multiple overlapping maxillary anterior teeth, and is often considered to be an esthetically favorable characteristic of the smiling face of a young woman. Therefore, investigating the differences in the interpretation of MxAC among orthodontists, orthodontic patients, and laypeople is expected to help improve the patient-doctor relationship under such circumstances.
The appearance of dental crowding in a smiling face can significantly affect the results of estimates of the social attractiveness of the person. , In previous studies, laypeople generally evaluated smiling facial photographs with crowded anterior teeth as less attractive than smiling facial photographs with normally aligned anterior teeth regardless of the level of attractiveness of the background face. For example, Olsen and Inglehart used smiling facial photographs of dental students in the United States. The area inside the borders of the lips of each smiling facial image was replaced with an image depicting anterior teeth with normal occlusion or 1 of 6 types of malocclusion including crowding. The attractiveness of each modified facial photograph with a simulated dental appearance was evaluated by 889 adult laypeople using a visual analog scale (VAS). Consequently, a significantly lower level of attractiveness was observed in the smiling facial photographs with crowded anterior teeth when compared with normal occlusion. In Singapore, Soh et al investigated the relationship between dental attractiveness and malocclusion type. Twenty-one orthodontists and 158 adult laypeople evaluated the attractiveness of 50 pairs of frontal and right buccal views of intraoral photographs with various types of malocclusions using a VAS. A significant relationship was observed between the dental attractiveness and the severity of MxAC only in the laypeople. Interestingly, the findings of these previous studies on the effect of MxAC on evaluations of facial appearance and dental appearance were in agreement for laypeople, but not for orthodontists. In addition to the professional education and experience possessed by orthodontists, baseline level of interest in malocclusion and/or previous history of orthodontic treatment could be other factors that affect laypeople’s evaluations of the attractiveness of facial photographs, , regardless of the evaluator’s age, sex, or ethnicity.
In addition to the smiling face, evaluations of the proportion and symmetry of the face at rest are essential clinical examination items in orthodontic diagnosis. One of the characteristics of an attractive face is balanced frontal vertical facial proportions. In a previous study, digitally altering the lower facial height proportions of frontal facial silhouettes decreased evaluations of attractiveness. Another previous cephalometric study examined the craniofacial morphology of orthodontic patients with MxAC and found a significantly hyperdivergent skeletal pattern when compared with subjects with nonorthodontic normal occlusion. However, the influence of the hyperdivergent skeletal pattern of MxAC on the attractiveness of resting frontal faces has not been clarified. Furthermore, the influence of facial expression on the attractiveness of faces with and without malocclusion has not been thoroughly investigated. Although the crowded anterior teeth are not visible in the face at rest, it is necessary to investigate the resting facial attractiveness of patients with MxAC and compare it with the attractiveness of their faces when smiling.
The purposes of the present study were to compare the ratings of the attractiveness of resting and smiling frontal facial photographs with and without MxAC, and the interpretation of MxAC between orthodontists and laypeople with and without previous orthodontic treatment experience in Japan.
Material and methods
This was an observational cross-sectional study that was approved by the ethics committee of the Nippon Dental University (approval number: T2017-24).
According to the result of a previous study, G∗power statistical software (version 3.1; Heinrich Heine University Düsseldorf, Düsseldorf, Germany) was used to determine that the required minimum sample size for the number of evaluators for each evaluator group would be 30 to achieve the target effect size of 0.675 with 0.8 power at 5%.
The selection of subjects with normal occlusion and patients with MxAC was performed according to the method used in a previous study.
Standardized frontal facial photographs of the 33 female subjects with normal occlusion and the 33 female patients with MxAC at rest and in posed smiling were evaluated and selected by 2 orthodontists (A.Y. and K.A.). The inclusion criterion was gingival exposure within 0-2 mm during the posed smiling. The exclusion criteria were as follows: (1) abnormally colored crowns in the visible teeth of the posed smile and (2) significant distractions, such as a facial tattoo or extreme hairstyle. Consequently, 20 female subjects and 22 female patients were selected to undergo further screening to make the age ranges between the 2 groups as close as possible. Ultimately, frontal facial photographs of 12 subjects from the control group (mean age, 20.1 ± 0.7 years; range, 19-21 years) and 12 patients from the MxAC group (mean age, 21.7 ± 2.6 years; range, 18-26 years; arch length discrepancy in the maxillary dental arch: 10.00 ± 3.94 mm) were selected as photographs of normal models and MxAC models, respectively. Each photograph was trimmed to a 5:4 aspect ratio and the eyes were obscured with a blur box using image processing software (Photoshop; Adobe, San Jose, Calif), and printed on 1 piece of A4-size paper at a fixed width of 100 mm along with a 100-mm VAS. , For confirmation of interevaluator and intraevaluator reliabilities, evaluation sheets with resting and smiling images of 3 randomly selected models from each group were duplicated. Consequently, 30 evaluation sheets with resting and smiling images were randomly sorted into resting and smiling sets, respectively. An evaluation booklet with a total of 60 evaluation sheets including both resting and smiling sets was created ( Fig 1 ).
Forty-two orthodontists (25 females, 17 males; mean age, 35.6 ± 9.4 years; range, 27-66 years) were recruited from the faculty of the Department of Orthodontics based on the following inclusion criteria: (1) completed a 2-year full-time postgraduate orthodontic program and (2) Japanese nationality. Forty-two laypeople with previous orthodontic treatment (34 females, 8 males; mean age, 26.1 ± 7.5 years; range, 16-47 years) were recruited as the patient group from the nondental personnel of the Nippon Dental University, students and faculty of the Tokyo University of Marine Science and Technology, and faculty and guardians of the Seiga-Tenshi Preschool in Saitama Prefecture based on the following inclusion criteria: (1) aged 16 years or older, (2) previous orthodontic treatment, (3) no specialized education in dentistry, and (4) Japanese nationality. Forty-six laypeople without previous orthodontic treatment (27 females, 19 males; mean age, 29.8 ± 10.2 years; range, 16-58 years) were recruited from the nondental personnel of the same universities and guardians of the same preschool based on the following inclusion criteria: (1) aged 16 years or older, (2) no history of orthodontic treatment, (3) no specialized education in dentistry, and (4) Japanese nationality. To reduce the potential for bias owing to a difference in evaluator age, the maximum age for inclusion in the groups of orthodontists and laypeople without previous orthodontic treatment was matched to the maximum age of the patient group with the lowest maximum age (47 years). Consequently, 38 orthodontists (25 females, 13 males; mean age, 33.0 ± 4.7 years; range, 27-45 years; mean clinical experience, 7.0 ± 4.5 years; range, 2-19 years; 11 full-time faculty members, 27 part-time faculty members) and 43 laypeople without previous orthodontic treatment (24 female, 19 male; mean age, 28.0 ± 7.9 years; range, 16-45 years) were selected for inclusion in the orthodontist and layperson groups, respectively. To reduce the potential for biased responses, before participating in the present study, all evaluators were ambiguously informed that the purpose of the present study was to “help understand facial perceptions using subjective evaluations” and signed a written consent form. One evaluation booklet was given to each evaluator. The evaluators were instructed to refrain from returning to the previous evaluation sheet after proceeding to the next evaluation sheet, and VAS evaluations were conducted individually in a quiet room prepared for the present study according to the method described in the previous studies. , There was no time limit, and evaluators were informed that if they became fatigued, they could take a rest. All evaluators completed the VAS evaluation within 3 minutes, and no evaluator complained of fatigue.
After the VAS session, evaluators’ interpretations of MxAC were evaluated using a questionnaire in Japanese. Evaluators were asked to select any words they felt closely represented the meaning of MxAC from a list of terms that appear in the literature. , , The listed words were cute, , youthful, , feminine, , crooked teeth, , and unclean (bad or poor oral hygiene).
After completing the questionnaire session, all evaluators were told the actual purpose of the study. All evaluators in the patient and layperson groups received a 500-yen (approximately U.S. $4.50) gift certificate in appreciation of their participation.
To evaluate the intraexaminer reliability of the VAS measurements, 10 evaluation booklets were randomly selected and remeasured by 1 evaluator (A.Y.) at an interval of at least 2 weeks. For interexaminer reliability, the same evaluation booklets were reanalyzed by another orthodontist. The intra and interexaminer reliabilities were calculated using Dahlberg’s formula.
To confirm the interevaluator and intraevaluator reliabilities of the VAS evaluations, intraclass correlation coefficients were calculated for each evaluator group.
Because the results of the VAS evaluation did not show normal distributions according to the Kolmogorov-Smirnov test, medians and interquartile ranges were calculated, and the Mann-Whitney U, Kruskal-Wallis, and Wilcoxon signed rank tests were used for comparisons between the model groups, evaluator groups, and conditions of facial images, respectively. The chi-square and Fisher exact tests were used to compare the results of the questionnaire responses between evaluator groups. All statistical analyses were performed using SPSS software (version 25; IBM, Armonk, NY). Significance levels were set at P <0.05.
The intraexaminer and interexaminer reliabilities for the VAS measurements were 0.07 mm and 0.36 mm, respectively.
The interevaluator reliability for the orthodontist, patient, and layperson groups were 0.889 (excellent), 0.882 (excellent), and 0.826 (excellent), respectively. The intraevaluator reliability for the orthodontist, patient, and layperson groups were 0.732 (good), 0.436 (fair), and 0.532 (fair), respectively.
For all evaluator groups, the median VAS score for facial attractiveness was significantly smaller in the MxAC models than in the normal models for both the resting ( P <0.01; Table I ) and smiling images ( P <0.01; Table II ).
|Evaluator group||Normal models||MxAC models||Mann-Whitney