Peer assessment of dental attractiveness

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Peer assessment of dental attractiveness Egle Ong,a Rebecca A Brown,b and Stephen Richmondc Cardiff, Wales, United Kingdom Introduction: The objectives of the study were to determine the relative importance of various dental features that contribute to overall dental attractiveness and to test the validity of the concepts of golden proportion and golden percentage as applied to the human dentition. Methods: Sixty 30-year-old subjects (29 men, 31 women) were selected from the 20-year longitudinal Cardiff Survey. Color photographs of the subjects’ dentitions were taken with the lips retracted so that their teeth and gums were clearly exposed. Twelve nondentists, aged 32 to 33 years, equally divided according to sex, rated the subjects’ dental appearances on a 5-point Likert attractiveness scale. The maxillary anterior teeth were measured, and relevant ratios were calculated and compared with the golden proportion. Factor analyses and linear regression were used to investigate the hierarchy of dental features, and variance components analysis was used to estimate interrater agreement. Results and conclusions: Overall dental attractiveness did not depend on any particular feature of the dentition. A hierarchy of various features was established, with crown shape ranked highest, and tooth and gum color ranked lowest. The golden proportion and the golden percentage were not decisive factors in determining dental attractiveness. (Am J Orthod Dentofacial Orthop 2006;130:163-9)

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hysical attractiveness influences a peron’s life in various ways and to a considerable extent.1-3 Moreover, facial appearance has been suggested to be a slightly more powerful predictor of overall attractiveness than the body.4 Recently, it was reported that all facial features are similarly important in making one’s face attractive (in children and adults alike) as judged by laypeople in their early 30s.5 The importance of one’s dental appearance in overall facial attractiveness when impressions are formed should not be overestimated. Nevertheless, there is evidence that people with impaired dental appearance are highly likely to be perceived substantially differently from those having healthy-looking dentitions.6-13 The evidence about the long-term effects of various factors that can affect overall dental attractiveness is somewhat scarce. However, it was suggested that malocclusion might adversely affect body image and self-concept not only in adolescence but also in adulthood.14 Factors that might affect overall dental appearFrom the Department of Dental Health and Biological Sciences, School of Dentistry, Wales College of Medicine, Biology, Life and Health Sciences, Cardiff, Wales, United Kingdom. a Visiting scholar. b Medical statistician. c Professor. Reprint requests to: Stephen Richmond, Department of Dental Health and Biological Sciences, School of Dentistry, Wales College of Medicine, Biology, Life and Health Sciences, Heath Park, Cardiff CF14 4XY, Wales, United Kingdom; e-mail, [email protected] Submitted, September 2004; revised and accepted, February 2005. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.02.018

ance could be classified as related to single teeth (size, color, shape), adjacent teeth (proportions and alignment), and periodontium (gingival color, contour, and texture).15,16 The area of most esthetic importance is likely to be the maxillary anterior teeth because of their high visibility in an average open smile.17 Some dental esthetic factors can be evaluated by subjective judgment—ie, attractiveness of tooth shape18 or color.19 In addition, the esthetic value of other features, such as crown proportions or symmetry across the midline, can be objectively assessed with specific measures, such as the golden proportion20,21 or its modification, the golden percentage.22 The width-to-height ratio of the maxillary central incisors has been suggested to be significant in terms of overall dental appearance because these teeth normally dominate in a person’s smile.20 For the golden proportion, the width-to-height ratio of a maxillary central incisor crown would be equal to 0.62. The golden proportion takes into consideration the relative widths of the maxillary anterior teeth and assumes that in an attractive dentition the ratio of the apparent widths of the central incisor to the lateral incisor is 1.62:1; similarly, the apparent width of the lateral incisor is in the golden proportion to the width of the canine—ie, 1:0.62.21 The golden percentage is a modification of the golden proportion rule, and it was proposed as a simple and objective tool to assess such dental esthetic measures as anterior dominance, symmetry across the midline, and regressive proportion.22 In spite of much literature about esthetic dentistry, 163

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it is still not possible to definitively state which features make dental appearance attractive. Few studies have attempted to estimate the potential of various dental characteristics or determine a hierarchy of factors contributing to an attractive dentition,19 and none took all esthetic dental features into account while assessing their significance in overall dental attractiveness when impressions are formed. The aim of this study was to investigate various factors that contribute to overall dental attractiveness. The objectives were (1) to determine the relative importance of various dental features (alignment; tooth color, shape, size, and crown proportions; dentition proportions; gum color and contour) and their contribution to overall dental attractiveness and (2) to test the validity of the golden proportion (and the golden percentage) as applied to the human dentition. SUBJECTS AND METHODS

In this study, we used data from the longitudinal Cardiff Survey, which began in 1981.23 Sixty white subjects (31 women, 29 men), aged 30, who represented a broad range of dental attractiveness, were selected from the sample of 331 (by using the average tooth attractiveness score obtained from a panel of 6 judges and derived from a 10-cm visual analog scale). Color photographs of the anterior dentitions were taken with the subjects’ lips retracted so that their teeth and gums were clearly visible. A questionnaire was devised with a 5-point attractiveness scale for various features of teeth and gums (tooth alignment, color, shape, size, teeth crown proportions, dentition proportions, gum color and contour) (Table I). In addition, the raters were asked to evaluate the overall attractiveness of each dentition. Supplementary definitions were added regarding the proportions of the teeth and the dentition to aid the rater. Sixty photographs were randomly organized into a folder with 1 questionnaire and photograph per page (to reduce the ordering effect). Twelve white nondentists, aged 32 to 33 years, equally divided according to sex, were invited to rate these dental photographs. The raters were asked to complete the questionnaires at home and return them within 3 days. Each rater was paid £20. The golden-proportion rule was applied to the maxillary central incisors. Incisal-gingival heights and mesiodistal widths of the clinical crowns were measured as seen from the front view by using digital photographic images and the cursor functions in PowerPoint 97 (Microsoft, Redmond, Wash). Width-toheight ratios were computed for both right and left

American Journal of Orthodontics and Dentofacial Orthopedics August 2006

maxillary central incisors (1 dentition was excluded because of a missing maxillary right central incisor). The principle of the golden percentage was used to assess the arrangement of the 6 maxillary anterior teeth while suggesting that, in the ideal case scenario (when the teeth are in the golden proportion), their relative widths should approximate the following percentages: 10% (right canine), 15% (right lateral incisor), 25% (right central incisor), 25% (left central incisor), 15% (left lateral incisor), and 10% (left canine).22 For the latter purpose, a subsample of 50 subjects was selected (dentitions with clearly visible gaps between the maxillary front teeth were excluded). The apparent widths of the 6 maxillary anterior teeth (right canine to left canine) were measured by using digital photographic images and the cursor functions in Microsoft PowerPoint 97. The mesiodistal widths of these teeth were added together, and the total width of the maxillary front segment accounted for 100%. In that way, the relative width of each tooth was calculated and assigned a respective percentage for each dentition. Statistical analysis

Factor and linear regression analyses were used to investigate individual dental features. Factor analysis aimed to identify any underlying factors of combined dental features that contribute to overall dental attractiveness. Regression analysis was used to determine how well each dental feature predicted the overall attractiveness score. Dental attractiveness scores were averaged over raters for these statistical analyses. As well as providing attractiveness scores, the raters designated each subject’s dentition as attractive or unattractive. A consensus was obtained for all 12 raters for each subject. If there was a tie, the subject was assigned to the unattractive group. Interrater reliability was assessed as the ratio of subject variance to the sum of subject, rater, and error variance determined from the variance components analysis.24 Unless otherwise stated, a P value of ⬍.05 was considered statistically significant. RESULTS

The results of the factor analysis are shown in Table II. Only 1 factor was extracted with similar weightings for all features. This suggests that each dental feature contributed approximately equally to overall dental attractiveness. This was true for the entire sample as well as for men and women, and the attractive and unattractive dentitions (as classified by the raters) separately. According to the linear regression analysis results (Table III), in both the entire sample and in the groups for sex and attractiveness, the dental feature most

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American Journal of Orthodontics and Dentofacial Orthopedics Volume 130, Number 2

Table I.

Five-point dental attractiveness rating scale Neither attractive nor unattractive

Very unattractive Overall dentition Teeth Alignment Color Shape Size Tooth-crown proportions* Dentition proportions† Gums Color Contour

Very attractive

1

2

3

4

5

1 1 1 1 1 1

2 2 2 2 2 2

3 3 3 3 3 3

4 4 4 4 4 4

5 5 5 5 5 5

1 1

2 2

3 3

4 4

5 5

Women

Men

*Defined as width-to-length ratio of crown. Defined as width-to-length ratio of entire dentition.



Table II.

Factor loadings and communalities for factor analysis of dental features Entire sample

Dental feature

Factor loading

Alignment Tooth color Shape Size Crown proportions Dentition proportions Gum color Gum contour Variance explained

.136 .116 .145 .143 .144 .140 .128 .140 83.7%

Com .825 .602 .940 .914 .926 .874 .730 .884

Attractive Factor loading .157 .108 .169 .151 .165 .160 .153 .158 66.2%

Unattractive

Com .690 .325 .801 .638 .766 .723 .658 .699

Factor loading .140 .103 .158 .155 .155 .147 .130 .151 75.8%

Com .722 .394 .914 .890 .890 .796 .622 .839

Factor loading .135 .121 .144 .145 .145 .138 .126 .139 83.4%

Com .808 .649 .924 .931 .937 .846 .708 .864

Factor loading .137 .111 .148 .142 .144 .142 .129 .143 82.7%

Com .821 .541 .954 .884 .904 .887 .724 .898

Com, Communality.

Table III.

Results of linear regression for each dental feature with overall attractiveness score R2 values from univariate linear regressions

Dental feature Alignment Tooth color Shape Size Crown proportions Dentition proportions Gum color Gum contour

Entire sample

Attractive

Unattractive

Women

Men

.831 .632 .864 .814 .837 .820 .605 .740

.698 .388 .764 .555 .674 .628 .402 .458

.725 .462 .773 .707 .716 .668 .484 .630

.796 .685 .857 .820 .822 .785 .577 .706

.853 .561 .864 .778 .834 .839 .599 .766

P ⬍ .01.

strongly associated with overall attractiveness was tooth shape. The dental features least associated with overall score were color of teeth and gums. As can be seen from Table IV, generally, the scores for all dental features as well as overall dental attrac-

tiveness were significantly higher in the attractive dentition group. The overall dental attractiveness score in women was significantly higher than in men. Similarly, tooth size, crown proportions, and dentition proportions were

166 Ong, Brown, and Richmond

Table IV.

American Journal of Orthodontics and Dentofacial Orthopedics August 2006

Mean scores (standard deviations) for various dental features by dentition attractiveness and sex

Attractiveness Attractive (n ⫽ 16) Unattractive (n ⫽ 44) P Sex Female (n ⫽ 31) Male (n ⫽ 29) P

Overall

Alignment

Tooth color

Shape

Size

Teeth crown proportions

Dentition proportions

Gum color

Gum contour

3.5 (.43) 2.1 (.60) .000

3.5 (.38) 2.4 (.66) .000

3.5 (.35) 2.6 (.63) .000

3.5 (.30) 2.5 (.59) .000

3.4 (.31) 2.5 (.53) .000

3.3 (.26) 2.5 (.48) .000

3.4 (.42) 2.3 (.57) .000

3.3 (.44) 2.6 (.54) .000

3.3 (.37) 2.5 (.52) .000

2.7 (.86) 2.3 (.77) .045

2.8 (.76) 2.4 (.75) .054

2.9 (.71) 2.7 (.66) .276

2.9 (.67) 2.6 (.69) .069

2.9 (.62) 2.5 (.57) .013

2.9 (.56) 2.5 (.55) .018

2.8 (.71) 2.3 (.68) .012

3.0 (.60) 2.7 (.58) .098

2.8 (.56) 2.6 (.63) .073

rated significantly more attractive in the female subjects. The average maxillary central incisor ratio was found to be just above 0.8 (Table V) and therefore was generally higher than the golden proportion (0.62) for our sample. The mean ratios for the central incisors did not differ significantly between the men and the women. Interestingly, the central incisor’s width-to-height ratio was significantly greater in the unattractive group (for the left central incisor only). Table VI shows the results of the golden percentage analysis, suggesting that, in this sample, average dentition was more or less symmetrical across the midline, with the maxillary central incisors occupying just above 46% (slightly less than the golden 50%). Interestingly, a similar pattern remained when studied in separate sex and dental-attractiveness groups; generally, differences between the relative widths of the teeth were not statistically significant (except that men had wider right canines than the women, and attractive dentitions had wider right lateral incisors than unattractive dentitions). From variance components analysis, the following results were obtained for interrater reliability, with ␴2 as the variance for each component: R ⫽ ␴2SUBJECTS ␴2SUBJECTS ⫹ ␴2RATERS ⫹ ␴2ERROR ⫽

0.669 0.669 ⫹ 0.182 ⫹ 0.403

⫽ 0.53

The interrater agreement of 0.53 could be regarded as moderate for assessing a person’s dental attractiveness. DISCUSSION

The need for “a very detailed, almost histologic approach to dental aesthetics” was highlighted in the early 1970s,20 and attempts since then have been made to address what makes a smile attractive.

Table V.

Mean ratios (standard deviations) for maxillary right and left central incisors (entire sample and groups by dentition attractiveness and sex)

Entire sample (n ⫽ 59) Attractiveness Attractive (n ⫽ 16) Unattractive (n ⫽ 43) P Sex Female (n ⫽ 31) Male (n ⫽ 28) P

Right central incisor

Left central incisor

.83 (.09)

.82 (.09)

.80 (.10) .84 (.08) .061

.78 (.10) .83 (.08) .046

.82 (.08) .84 (.10) .526

.81 (.10) .82 (.08) .907

Several studies attempted to evaluate the significance of various dental features in terms of overall dental attractiveness, most of them considering only 1 feature or a few features.18,25 Dunn et al19 assessed the importance of several dental features: symmetry, tooth shade, number of teeth displayed, height of maxillary lip line, and number of natural-looking teeth. Nevertheless, other elements, such as gingival appearance, tooth shape, and tooth proportions, were not evaluated. It was suggested that the cumulative visual impact of the anterior dentition often transcends the sum of the individual parts.26 In this study, we investigated dental esthetics and considered as many dental factors as possible. Both subjective and objective measures were used and their importance assessed in overall dental attractiveness. Although all dental features investigated contributed similarly to overall dental attractiveness, a hierarchy of features was established. Interestingly, tooth shape was most strongly associated with overall attractiveness, whereas the color of teeth and gums had the weakest association with the overall score (although still statistically significant). Only very minor changes in the ranking order occurred when the sex of a subject or the attractiveness of a dentition was considered.

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Table VI. Mean values (standard deviation) of golden percentage calculations (entire sample and groups by dentition attractiveness and sex) Golden % 10 %

Entire sample (n ⫽ 50) Attractiveness Attractive (n ⫽ 16) Unattractive (n ⫽ 34) P Sex Female (n ⫽ 28) Male (n ⫽ 22) P

15 % Right

25 %

25 %

15 %

10 %

Left

Canine

Lateral incisor

Central incisor

Central incisor

Lateral incisor

Canine

13.2 (2.1)

14.4 (1.7)

23.2 (1.4)

23.1 (1.2)

13.9 (1.9)

12.3 (1.7)

13.0 (1.8) 13.3 (2.2) .634

15.1 (1.1) 14.1 (1.9) .022

22.8 (1.1) 23.3 (1.4) .193

22.8 (1.2) 23.3 (1.2) .139

14.6 (1.3) 13.6 (2.1) .085

11.9 (1.4) 12.5 (1.9) .247

12.5 (2.0) 14.0 (1.9) .012

14.6 (1.7) 14.1 (1.7) .314

23.3 (1.4) 23.1 (1.4) .606

23.2 (1.1) 23.0 (1.2) .488

14.3 (1.3) 13.5 (2.4) .141

12.2 (1.6) 12.4 (2.0) .604

It was not unexpected that the gingival features— color and contour—were less significant than most tooth characteristics (except color). A possible explanation for this is that the gums are normally less visible than the teeth during daily interaction and thus less noticeable to laypeople than to dental professionals, who observe gingival structures daily. Also, our subjects did not have major gingival problems. The finding that tooth color was least associated (apart from the gingival characteristics) with overall dental attractiveness was somewhat unexpected and is in contrast to the findings of another relevant study in which it was concluded that tooth shade was the most important variable in predicting dental attractiveness.19 However, a comparison of those results and our findings should be made with care because the methods, and the dental features studied, differed considerably. Furthermore, it was recently reported that tooth whiteness was not associated with increased overall facial attractiveness as perceived by other people.27 In this context, the esthetic value of tooth color and its perception is still a poorly researched area. Nevertheless, from the present evidence, it seems safe to suggest that the stereotypical “the whiter the teeth, the more attractive they look” might not be completely true. Interestingly, the shape of the teeth stood out as a feature most strongly associated with overall dental attractiveness, both generally and in the sex and dentition-attractiveness groups. It is beyond the scope of this article to determine what tooth shape was preferred by the panel, but it seems worthwhile for future investigation. The findings regarding the proportions of the dominant teeth in one’s smile are in line with earlier findings by other researchers. The golden proportion (the ratio of 0.62) is not generally found in the central

incisors of the general population.28,29 Also, the golden proportion was not considered exceptionally attractive in an experimental setting.18,25 The average maxillary central incisor width-to-height ratio in this study was just over 0.8 and did not differ significantly between men and women. The proportion was slightly less in the attractive group; however, the difference was significant for the maxillary left central incisors but not for the right. The golden proportion principle for the esthetic evaluation of the maxillary front teeth was strongly advocated by Levin.21 However, others suggested that the regressive proportion of 0.62 was “too strong for dental use,”20 and, moreover, that it rarely occurs in a natural dentition.30 It was stated that the exact proportions are not as important as the concepts of symmetry and a logical approach to esthetic restoration of the maxillary anterior teeth.31 Furthermore, the application of a greater regressive proportion was suggested.32,33 The principle of the golden percentage was used for evaluation of the width of each maxillary front tooth for its contribution to symmetry, dominance, and proportion of the entire anterior segment. Our findings are mainly in line with previously reported relevant data. Generally, the maxillary central incisors were found to be the dominant element of the average dentition while occupying slightly less than the suggested golden 50% of the total width of the anterior segment. 22 The proportions of the maxillary central incisor crowns and the relative maxillary front teeth widths remained rather constant in the sex and dentitionattractiveness groups. Therefore, it can be concluded that in this sample the golden proportion was not the decisive factor when assessing dental attractiveness. In addition, the relative widths of the maxillary anterior

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teeth and the crown proportions of the maxillary central incisors could not be used as specific measures to distinguish women’s dentitions from men’s. It is plausible that, as long as the maxillary central incisors are a dominant element of the dentition, the maxillary front teeth are just about symmetrical across the midline and their relative widths decrease gradually and proportionally as seen from the front, the dentition can be considered attractive even if the relative width proportions deviate from the golden percentage. It is known that the perception of dental esthetics varies significantly among people of different ages and occupations, and depends on the level of education.18,34 In addition, various environmental factors— eg, lighting conditions— have been reported to influence the perception of tooth color35 and, most probably, other dental features. Therefore, because of these factors and because esthetic evaluation always has a lesser or a greater amount of subjectivity, a certain amount of perception variability is expected2,5 Interrater agreement for dental attractiveness in this study was moderate. Nevertheless, it could differ considerably if the panel included judges with different demographic characteristics. CONCLUSIONS

1. Overall dental attractiveness did not depend on any particular feature of the dentition; nevertheless, a hierarchy of various features was established, with crown shape ranked the highest, and tooth and gum color ranked the lowest. 2. The golden proportion and the golden percentage were not decisive factors in determining dental attractiveness. We thank Professor Bill Shaw, the principal investigator for the longitudinal Cardiff Study, and Anne Kingdon for maintaining contact with the subjects and organizing the recall program and database. We acknowledge funding from the NHS Research and Development Program.

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