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Tooth shape preferences in an esthetic smile
ORIGINAL ARTICLE
Tooth shape preferences in an esthetic smile Kurt M. Anderson,a Rolf G. Behrents,b Thomas McKinney,c and Peter H. Buschangd Texarkana and Dallas, Tex, and Saint Louis, Mo Introduction: The purpose of this study was to evaluate the contributions of tooth shape to the esthetic smile. Methods: Restorative dentists (120), laypeople (102), and orthodontists (113) evaluated a series of color photographs of men’s and women’s smiles. The photographs were randomly presented to test the effects of 3 different shapes of maxillary incisors and canines on the same patient. Results: For women, orthodontists preferred round and square-round incisors (P ⬍ .01), and restorative dentists preferred round incisors (P ⱕ .03). Laypeople did not discriminate between incisor shapes. For men, all 3 groups preferred square-round incisors (P ⱕ .042). There was also a tendency for male judges to rate female images more attractive than did female judges. Conclusions: Restorative dentists, orthodontists, and laypeople share similarities and display differences when considering esthetic preferences in tooth shape. Although there was no consensus in preference among the laypeople as a group, their preferences differed from those of the dental professionals. (Am J Orthod Dentofacial Orthop 2005;128:458-65)
D
entistry has experienced a paradigm shift from an emphasis on restoration to elective cosmetic treatment.1 In the same way, orthodontics has begun to emphasize dentofacial esthetics in addition to functional occlusal relationships. Although dental professionals are subject to the same environmental trends and media perspectives, educational experiences might bias clinicians’ esthetic preferences away from those of the public.2,3 Dentists are obligated to understand beauty, harmony, balance, and proportion as perceived by society when planning treatment.4 The importance of beauty and attractiveness in today’s society has been well established. Physically attractive people are perceived to be more kind, sensitive, interesting, strong, poised, modest, sociable, outgoing, exciting, and responsive.5 It is also believed that attractive people are more likely to obtain better jobs, have more successful marriages, and experience happier, more fulfilling lives. These societal biases begin early in life6 and impact a person’s future for a lifetime.7-11 Dentofacial attractiveness is particularly important to a person’s psychosocial well being. People with a normal dental appearance are judged more socially attractive over many personal characteristics than those a
Private practice, Texarkana, Tex. Professor of orthodontics, Saint Louis University, Saint Louis, Mo. c Associate professor of restorative sciences, Baylor College of Dentistry, Dallas, Tex. d Professor of orthodontics, Baylor College of Dentistry, Dallas, Tex. Reprint requests to: Dr Peter H. Buschang, Department of Orthodontics, Baylor College of Dentistry, Texas A & M University System Health Science Center, 3302 Gaston Ave, Dallas, TX 75246; e-mail, [email protected] Submitted, April 2004; revised and accepted, July 2004. 0889-5406/$30.00 Copyright © 2005 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.07.045 b
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with malocclusions.12 Those with poor dental esthetics have been linked to lack of self-confidence and are thought to be disadvantaged in social, educational, and occupational settings.13,14 During interpersonal interactions, the eyes primarily scan other people’s eyes and mouths, with little time spent on other features.15 Thus it is not surprising that the general public considers the smile to rank second only to the eyes when considering features most important to facial esthetics.3 Despite the importance of dental esthetics, little has been done to understand the contribution of the smile’s components. One such component is tooth shape. Many notions held today on the esthetics of tooth shape are based on authoritative writings aimed at guiding denture tooth selection. For example, Williams16 suggested that tooth shape should be determined by facial form. However, selecting tooth shape on the basis of facial form has not been supported by the literature. In fact, several studies have found no correlation between facial outline and actual or preferred tooth shape.17-19 Other popular methods for selecting tooth shapes in the past were based on stereotypes: women should have round, soft, and delicate teeth (tapering/ovoid); men should have square, angular teeth.20,21 But the validity of these stereotypes in tooth selection was called into question when dentists, dental students, and patients were asked to assess “masculine” and “feminine” tooth arrangements, and all subjects preferred the “masculine” arrangements.2 Thus, many traditional concepts on ideal tooth shape have not withstood the evidencebased litmus test. Because of the limited studies evaluating the esthetics of tooth shape, this study was designed to test the following null hypotheses: (1) a change in maxillary tooth shape will have no effect on
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Table I.
Demographic characteristics of judges Sex
Age (y)
Group
N
Men
Women
Unspecified
21-30
31-40
41-50
51-60
⬎60
Unspecified
Restorative dentists Laypeople Orthodontists
120 102 113
94 21 97
22 80 16
4 1 0
11 19 10
22 24 24
40 41 31
30 11 29
14 5 20
3 2 ⫺1
Fig 1. Survey design. Two booklets contained male smiles and 2 contained female smiles. Photographs were presented randomly, 3 smiles per page for incisor and canine shapes and 5 per page for lateral incisor positions.
esthetic preferences and (2) there will be no differences in esthetic scores between restorative dentists, laypeople, and orthodontists. MATERIAL AND METHODS
Three groups of judges were recruited: restorative dentists, laypeople, and orthodontists (Table I). The restorative dentists included both general dentists and prosthodontists from various Texas dental societies and some part-time restorative faculty in the restorative, prosthodontic, and Advanced Education in Graduate Dentistry programs at Baylor College of Dentistry. Laypeople were selected from consenting persons in the Baylor College of Dentistry waiting room areas. The orthodontic sample was obtained from 3 national orthodontic meetings and part-time faculty at 4 university orthodontic programs. The judges each evaluated 18 color photographs of smiles portrayed in either a male or female booklet (Fig 1). Pages 1-3 tested incisor shape preferences while maintaining canine shape. Pages 4-6 tested canine shape preferences while maintaining incisor shape. The photographs on each page were randomly grouped, and only 1 variable (incisor or canine shape) was tested on each page. The nose and chin were eliminated from the photographs to reduce the number of confounding variables. The female photographs, obtained from the Lorin Library,22 showed 18 unique veneer restorations for the
6 maxillary anterior teeth performed on 1 person. These veneers included 3 shapes based on the incisal line angles of the central and lateral incisors: square, square-round, and round. Three canine shapes were also compared: pointed, round, and flat. The various tooth shapes were evaluated in the same mouth by using try-in paste. Standardized photographs were taken with the Kodak 290 digital camera after placing fresh lipstick and having the patient smile naturally with the upper and lower teeth slightly apart. Figure 2 shows the first page of the female booklet, illustrating square-round incisors with flat canines, square incisors with flat canines, and round incisors with flat canines. The male photographs were created with Digident (Digident.com, Coral Springs, Fla) software. The intraoral photographs of the female patient were morphed onto a single male smile. Figure 3 shows page 4 of the male booklet, evaluating canine preferences with square-round incisors. A visual analog scale (VAS) beside each photograph was used to record the judges’ ratings. Each judge was directed to evaluate only the maxillary teeth and to mark on the VAS beside each photograph. Written instructions explained that the marking along the VAS indicated how attractive they judged the maxillary teeth to be. The center line on the VAS indicated average attractiveness, and marks located to the right or the left indicated progressively more or less
460 Anderson et al
Fig 2. Female incisor shape with flat canines. Incisor shapes: Sr, square-round; S, square; R, round. Canine shape: F, flat.
American Journal of Orthodontics and Dentofacial Orthopedics October 2005
Fig 3. Male canine shapes with square-round incisors. Incisor shape: Sr, square-round. Canine shapes: P, pointed; F, flat; R, round.
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Table II. Variable Incisors
Female incisor shape preferences of restorative dentists, laypeople, and orthodontists Restorative dentists Mean
Incisors with flat canines Sr 57.1 S 46.6 R 69.1 P ⬍ .05 R ⬎ Sr ⬎ S Incisors with round canines Sr 62.7 S 47.5 R 65.8 P ⬍ .05 R ⬎ S; Sr ⬎ S Incisors with pointed canines Sr 54.7 S 46.2 R 63.0 P ⬍ .05 R ⬎ Sr ⬎ S
Laypeople
Orthodontists
SD
Mean
SD
14.7 17.1 22.8
67.1 66.1 73.7 R⬎S
19.2 19.8 18.0
16.3 17.1 22.1
65.1 65.8 69.4
18.1 17.5 21.9
64.5 64.1 65.6
SD
P
Post-hoc
58.9 47.8 71.2 R ⬎ Sr ⬎ S
16.4 17.0 19.2
.005 ⬍.001 .497
D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L
19.5 19.9 19.5
61.3 51.3 64.4 R ⬎ S; Sr ⬎ S
15.1 17.9 19.7
.513 ⬍.001 .429
21.9 18.9 20.8
61.2 50.7 64.5 R ⬎ S; Sr ⬎ S
17.6 14.7 19.6
.028 ⬍.001 .800
attractive maxillary teeth, respectively. The distance from the left end of the VAS was expressed as a percentage of the total VAS. Judges were also asked to indicate their sex, age category, and race by checking the appropriate boxes, but to make no other identifying marks. A pilot study was conducted to validate the survey instrument. Six experienced orthodontists (10⫹ years experience) and 10 randomly chosen laypeople completed the initial survey instrument and were asked a series of questions designed to determine whether they understood the instructions and what the marks on the VAS meant to them. They were also asked what they thought they were evaluating and whether they evaluated the photographs individually or made comparisons within or across pages. Based on the responses from this pilot study, the instructions were modified to more clearly indicate the sex in the photographs and to specifically instruct the judges to focus their evaluation on the maxillary teeth. The variables were distributed normally based on the skewness and kurtosis statistics. Paired t tests were performed to test for significant differences in preference of tooth shape and lateral incisor position in each group. Because of the differences in sex distributions among groups, a 3-way ANOVA with interaction was performed. The initial analysis consisted of a 3-way ANOVA testing for the effects of sex, age group, professional group, and their interactions. The analyses were performed separately for the male and female photographs. Age was significant in only 2 of the 36 comparisons and was therefore excluded from further analysis. Once age was removed, there was no interaction between the other factors.
Mean
ANOVA differences
D ⬍ L; O ⬍ L
D⬍L D ⬍ L; O ⬍ L
RESULTS
With 1 exception, laypeople did not significantly discriminate between any of the female incisor shapes (Table II). Restorative dentists and orthodontists, on the other hand, preferred round and square-round incisors over square incisors in the female images (P ⬍ .001). In addition, restorative dentists preferred round incisors over square-round incisors (P ⱕ .03) for most of the female dental arrangements. When evaluating male images (Table III), all 3 groups preferred square-round incisors over square incisors (P ⱕ .001). Both professional groups rated square-round incisors significantly more attractive than round incisors (P ⱕ .042) in the male images. Orthodontists also tended to prefer round incisors over square incisor arrangements in the male images (P ⱕ .023). In general, laypeople scored all of the female images (Table II) much higher than the orthodontists and restorative dentists. Differences between laypeople and dental professionals were significant for squareround and square incisor shapes. No significant group differences were found when evaluating round incisors in the female images. However, restorative dentists rated round incisors significantly less attractive than either orthodontists or laypeople when evaluating the male images (Table III). Laypeople did not show a preference in canine arrangement for the female images (Table IV). Restorative dentists and orthodontists rated flat canines as more attractive than round canines with squareround incisors (P ⱕ .002). Both groups also rated the flat canines to be more attractive than pointed canines in the female images with round incisors (P ⱕ
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Table III. Variable Incisors
American Journal of Orthodontics and Dentofacial Orthopedics October 2005
Male incisor shape preferences of restorative dentists, laypeople, and orthodontists Restorative dentists Mean
Incisors with flat canines Sr 58.9 S 50.0 R 52.0 P ⬍ .05 Sr ⬎ R; Sr ⬎ S Incisors with round canines Sr 61.3 S 51.0 R 47.7 P ⬍ .05 Sr ⬎ R; Sr ⬎ S Incisors with pointed canines Sr 60.0 S 50.2 R 48.8 P ⬍ .05 Sr ⬎ R; Sr ⬎ S
Table IV.
Laypeople
Orthodontists
ANOVA differences
SD
Mean
SD
Mean
SD
P
Post-hoc
16.2 18.5 20.0
63.8 53.9 66.1 R ⬎ S; Sr ⬎ S
20.5 20.7 23.1
63.5 52.7 63.5 Sr ⬎ S; R ⬎ S
15.8 18.6 15.8
.234 .545 ⬍.001
D ⬍ L; D ⬍ O
16.1 16.2 21.7
65.3 54.7 56.3 Sr ⬎ R; Sr ⬎ S
18.0 19.9 21.4
66.0 54.3 60.4 Sr ⬎ R ⬎ S
15.2 16.1 15.6
.262 .474 .003
D ⬍ L; D ⬍ O
15.9 17.7 21.4
66.4 56.0 57.7 Sr ⬎ S
20.1 18.1 20.8
66.7 54.4 59.0 Sr ⬎ R; Sr ⬎ S
15.3 17.8 17.6
.07 .222 .014
D ⬍ L; D ⬍ O
Female canine shape preferences of restorative dentists, laypeople, and orthodontists
Variable
Restorative dentists
Canines
Mean
SD
Canines with square-round incisors P 54.9 19.0 F 59.5 16.3 R 53.7 15.8 P ⬍ .05 F⬎R Canines with round incisors P 55.5 19.0 F 63.0 20.0 R 58.3 21.6 P ⬍ .05 F⬎P Canines with square incisors P 44.7 17.0 F 43.2 17.7 R 45.6 20.8 P ⬍ .05
Laypeople Mean
Orthodontists
ANOVA differences
SD
Mean
SD
64.2 67.1 63.8
18.9 18.1 20.3
61.9 57.3 52.8 P ⬎ R; F ⬎ R
18.3 15.4 17.5
.027 .008 .003
62.8 67.9 64.4
19.4 22.3 18.7
61.6 65.7 65.4 F ⬎ P; R ⬎ P
19.0 19.3 17.1
.101 .466 .114
62.7 60.9 64.7
20.6 18.5 20.0
51.0 47.7 48.4 P⬎F
16.5 18.4 17.4
⬍.001 ⬍.001 ⬍.001
.025). Uniquely, orthodontists preferred pointed canines over flat canines with square incisors (P ⫽ .023) and round canines over pointed canines with round incisors (P ⫽ .022) in the female images. Restorative dentists did not make a significant distinction in preferences between canine arrangements in the male images (Table V). Orthodontists rated pointed and round canines significantly more attractive than flat canines when paired with square-round incisors in the male images (P ⱕ .005). Laypeople rated flat canines more attractive than round or pointed canines when paired with round incisors (P ⱕ .041). In addition, laypeople rated the female images significantly more attractive than did restorative
P
Post-hoc D ⬍ L; D ⬍ O D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L
D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L
dentists and orthodontists except for canine shapes associated with round incisors (Table IV). For the male images (Table V), orthodontists rated round incisors with the various canine arrangements significantly more attractive than restorative dentists (P ⱕ .020). Laypeople, on the other hand, rated square incisors with pointed and flat canine shapes significantly more attractive than restorative dentists (P ⱕ .026). In general, male judges tended to be less critical than female judges about female images (Table VI). Male judges rated female images with square-round and round incisors as more attractive than female judges (P ⱕ .04). They also judged flat canines more attractive than female judges (P ⱕ .037).
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Table V.
Male canine shapes preferences of restorative dentists, laypeople, and orthodontists Restorative dentists
Variable Canines
Mean
SD
Canines with square-round incisors P 59.9 16.4 F 55.9 17.8 R 58.7 16.2 P ⬍ .05 Canines with round incisors P 48.5 15.6 F 50.8 15.4 R 48.4 18.3 P ⬍ .05 Canines with square incisors P 47.0 14.5 F 46.5 15.2 R 47.9 15.2 P ⬍ .05
Table VI.
Laypeople
Orthodontists
ANOVA differences
Mean
SD
Mean
SD
P
Post-hoc
65.2 60.8 62.4
20.1 17.6 17.6
65.8 58.1 65.8 P ⬎ F; R ⬎ F
15.7 17.1 14.8
.141 .343 .067
54.3 60.7 54.1 F ⬎ P; F ⬎ R
17.8 17.1 18.0
59.1 59.0 57.6
17.3 17.7 16.5
.004 .005 .021
D⬍O D ⬍ L; D ⬍ O D⬍O
55.3 56.7 56.0
19.2 22.7 23.3
53.3 51.9 52.2
18.6 18.3 17.4
.036 .020 .083
D⬍L D⬍L
Sex differences in female images Variable
Male judges
Female judges
Incisors
Canine
Mean
SE
Mean
SE
P
Sr S R Sr S R Sr S R Sr Sr Sr S S S R R R
F F F R R R P P P P F R P F R P F R
61.2 53 72.3 63.7 54.3 65.6 59.3 52.6 65.5 60.3 61.3 57.9 60 67.3 63.7 50.9 50.6 50.3
2.1 2.3 2.3 2.1 2.2 2.4 2.3 2.1 2.4 2.4 2.1 2.3 2.3 2.5 2.3 2.2 2.2 2.4
54.9 49.4 60.5 56 47.1 58.3 53 48.3 55.2 53.8 55.8 48.3 58.6 56 57.5 46.8 41.3 46.3
3.3 3.6 3.7 3.3 3.6 3.8 3.6 3.3 3.9 3.7 3.3 3.6 3.6 3.9 3.7 3.5 3.5 3.7
.019 NS .003 .041 NS .033 .044 NS .015 NS .026 .006 NS .007 NS NS .037 NS
NS, Not significant.
DISCUSSION
Restorative dentists’ incisor shape preferences appear to be consistent with traditional educational concepts, basing ideal tooth shape on sex stereotypes, which hold that men are thought of as square, angular, and rugged and should have square, more angled teeth, whereas women are soft, round, and delicate and should have more rounded teeth.21,23 For example, round incisors received the highest esthetic scores, and square incisors received the lowest for the female images. For
the male images, restorative dentists liked the squareround incisors the best and the round incisors the least. Orthodontists’ esthetic evaluations deviated from the restorative dentists. Even though they preferred rounded incisal angles for the female incisor shapes (round and square-round), they did not discriminate between them. Orthodontists as a group were more accepting of round incisors on the male images than were the restorative dentists and liked the square incisor arrangement the least.
464 Anderson et al
Laypeople liked all incisor shapes on the female image. However, for males, laypeople liked round incisors combined with flat canines and square-round incisors combined with round and pointed canines. Square incisors were the least preferred for males regardless of the canine shape. When considering function, the canine is all-important,24 but until now, little has been known about its esthetic impact. The results from this study indicate that the shape of the canine is relatively unimportant. All 3 groups seem to have focused on the incisors, devoting little attention to the canines. This might be because the canine makes up a small percentage of relative tooth display compared with the incisors from a front view or because dental professionals’ focus is often placed on canine function23,25 and Angle classification rather than canine shape. There are 2 possible explanations for the group differences regarding female incisor shape. First, there might have been a difference in the groups’ abilities to discriminate differences. Because restorative dentists had a single preference for female incisor shape in this study, one could conclude that they were better able to discriminate between incisor shapes than orthodontists (who liked both round and square-round incisors) and laypeople. Interestingly, Kokich et al26 found that orthodontists are more discriminating than general dentists when evaluating midline deviations and gingiva-to-lip distances. Perhaps the ability to discriminate is associated with familiarity; restorative dentists more often deal with incisor shape, while orthodontists more often deal with the variables tested by Kokich et al.26 Second, it is possible that an actual difference in preferences existed among groups. Brisman2 reported different esthetic preferences among dentists and laypeople when evaluating various shapes and symmetry of unisex maxillary anterior teeth. Interestingly, restorative dentists were even more critical than orthodontists when evaluating round incisors in men. An additional explanation for this difference could be that orthodontists are more accepting of round incisors because they work with more youthful male dentitions (which have less wear) than do the restorative dentists. As previously indicated, possible differences between the dental professionals and laypeople in both this study and that of Brisman2 might be due to educational bias because dentists are trained in tooth selection and to be critical when evaluating the dentition. With these possible explanations, it would be wise to involve the patient in treatment planning, whether it involves incisal-edge recontouring or complete restoration of the anterior dentition. The sex of the judge had a significant impact on the
American Journal of Orthodontics and Dentofacial Orthopedics October 2005
esthetic scores. Male judges clearly rated most of the female images more attractive than the female judges. The reverse trend was present in evaluations of male images, with the female judges tending to be less critical than the male judges. This supports other studies’ findings that people are less critical when evaluating attractiveness in the opposite sex.27,28 CONCLUSIONS
Orthodontists, restorative dentists, and laypeople share more similarities than differences when considering dental esthetic values. However, important differences between these groups were identified. Having a better understanding of these similarities and differences will allow practitioners to design treatment plans that consider the esthetic preferences of both the patient and the dental professional. Moreover, esthetic values can differ greatly among patients. Even though there were no clear preferences for the laypeople as a group, they expressed clear individual preferences. Therefore, treatment must be individualized so that the patient’s unique esthetic preferences can be incorporated.29,30 Based on the results of this study, the following conclusions can be made: 1. Restorative dentists preferred round incisors for the female images. Orthodontists preferred round and square-round incisors for the female images. Laypeople did not express a preference in female incisor shape. 2. All 3 groups preferred square-round incisors for the male images. 3. Canine shape played a less important role than incisor shape in the esthetics of the anterior dentition. 4. Lay people tended to be less critical than dental professionals. Restorative dentists tended to be more critical than both laypeople and orthodontists when evaluating round incisors in male images. 5. Male judges were less critical than female judges when evaluating female images. We thank Drs Lorin Berland for providing the female photographs from the Lorin Library and Amelia Williams and David Traub for their help in imaging the male smiles. REFERENCES 1. Qualtrough A, Burke F. A look at dental esthetics. Quintessence Int 1994;25:7-14. 2. Brisman AS. Esthetics: a comparison of dentists’ and patients’ concepts. J Am Dent Assoc 1980;100:345-52. 3. Goldstein R. Study of need for esthetics in dentistry. J Prosthet Dent 1969;21:589-98.
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4. Peck H, Peck S. A concept of facial esthetics. Angle Orthod 1970;40:284-318. 5. Dion KK, Berscheid E, Walster E. What is beautiful is good. J Pers Soc Psychol 1972;24:285-90. 6. Corter C, Trehub S, Boukydis C. Nurses judgment on attractiveness of premature infants. Infant Behav Dev 1978;1:373-80. 7. Clifford M, Walster E. The effect of physical attractiveness on teacher expectations. Sociol Educ 1973;46:248-58. 8. Clifford M. Physical attractiveness and academic performance. Child Study J 1975;5:201-9. 9. Rich J. Effects of children’s physical attractiveness on teacher’s evaluations. J Ed Res 1975;67:599-609. 10. Adams GR, La Voie JC. The effect of sex of child, conduct, and facial attractiveness on teacher expectancy. Education 1974; 95:76-83. 11. Cash TF, Gillen B, Burns DS. Sexism and “beautyism” in personal consultant decision making. J Appl Phychol 1977;62: 301-10. 12. Shaw WC, Rees G, Dawe M, Charles CR. The influence of dentofacial appearance on social attractiveness of young adults. Am J Orthod 1985;87:21-6. 13. Jenny J, Cons NC, Kohout FJ, Jacobsen JR. Relationship between dental esthetics and attributions of self-confidence [abstract]. J Dent Res 1990;69:204. 14. Adams GR. Physical attractiveness research. Hum Dev 1977;20: 217-39. 15. Miller AG. Role of physical attractiveness in impression formation. Psychol Sci 1970;19:241-43. 16. Williams JL. A new classification of human tooth forms with reference to a new system of artificial teeth. Dent Cosmos 1914;56:627-8.
17. Bell RA. The geometric theory of selection of artificial teeth. J Am Dent Assoc 1978;97:637-40. 18. Seluk L, Brodbelt R, Walker G. A biometric comparison of face shape with denture form. J Oral Rehab 1987;14:139-45. 19. Brodbelt RHW, Walker GF, Nelson D, Seluk LW. A comparison of tooth shape with tooth form. J Prosthet Dent 1984;52:588-92. 20. Marunick MT, Chamberlain BB, Robison CA. Denture esthetics: an evaluation of layman’s preferences. J Oral Rehab 1983;10: 399-406. 21. Frush JP, Fisher RD. Introduction to dentogenic restoration. J Prosthet Dent 1955;5:586-95. 22. Berland L, Traub DL. The Lorin Library smile selection workbook. 2001.Digident.com; Coral Springs: 23. Johnson DL, Stratton RJ. Fundamentals of removable prosthodontics. 1988. Quintessence; Chicago: p. 289 –305. 24. Okeson JP. Management of temporomandibular disorders and occlusion. 4th ed 1998. Mosby; Saint Louis: p. 120. 25. Ash MM. Wheeler’s dental anatomy, physiology, and occlusion. 6th ed1984. W. B. Saunders; . Philadelphia: p. 154 –75. 26. Kokich VO, Kiyak HA, Shapiro PA. Comparing the perceptions of dentists and laypeople to altered dental esthetics. J Esthet Dent 1999;11:311-24. 27. Tennis GH, Dabbs JM. Judging physical attractiveness: effects of judges’ own attractiveness. Pers Soc Psychol Bulletin 1975;1: 513-6. 28. Lerner RM, Karabenick SA. Physical attractiveness, body attitudes, and self-concept in late adolescents. J Youth Adoles 1974;23:307-16. 29. Chalifoux PR. Practice made perfect; perception esthetics: factors that affect smile design. J Esthet Dent 1996;8:189-92. 30. Peck S, Peck L. Selected aspects of the art and science of facial esthetics. Semin Orthod 1995;1:105-26.
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Tooth shape preferences in an esthetic smile Kurt M. Anderson,a Rolf G. Behrents,b Thomas McKinney,c and Peter H. Buschangd Texarkana and Dallas, Tex, and Saint Louis, Mo Introduction: The purpose of this study was to evaluate the contributions of tooth shape to the esthetic smile. Methods: Restorative dentists (120), laypeople (102), and orthodontists (113) evaluated a series of color photographs of men’s and women’s smiles. The photographs were randomly presented to test the effects of 3 different shapes of maxillary incisors and canines on the same patient. Results: For women, orthodontists preferred round and square-round incisors (P ⬍ .01), and restorative dentists preferred round incisors (P ⱕ .03). Laypeople did not discriminate between incisor shapes. For men, all 3 groups preferred square-round incisors (P ⱕ .042). There was also a tendency for male judges to rate female images more attractive than did female judges. Conclusions: Restorative dentists, orthodontists, and laypeople share similarities and display differences when considering esthetic preferences in tooth shape. Although there was no consensus in preference among the laypeople as a group, their preferences differed from those of the dental professionals. (Am J Orthod Dentofacial Orthop 2005;128:458-65)
D
entistry has experienced a paradigm shift from an emphasis on restoration to elective cosmetic treatment.1 In the same way, orthodontics has begun to emphasize dentofacial esthetics in addition to functional occlusal relationships. Although dental professionals are subject to the same environmental trends and media perspectives, educational experiences might bias clinicians’ esthetic preferences away from those of the public.2,3 Dentists are obligated to understand beauty, harmony, balance, and proportion as perceived by society when planning treatment.4 The importance of beauty and attractiveness in today’s society has been well established. Physically attractive people are perceived to be more kind, sensitive, interesting, strong, poised, modest, sociable, outgoing, exciting, and responsive.5 It is also believed that attractive people are more likely to obtain better jobs, have more successful marriages, and experience happier, more fulfilling lives. These societal biases begin early in life6 and impact a person’s future for a lifetime.7-11 Dentofacial attractiveness is particularly important to a person’s psychosocial well being. People with a normal dental appearance are judged more socially attractive over many personal characteristics than those a
Private practice, Texarkana, Tex. Professor of orthodontics, Saint Louis University, Saint Louis, Mo. c Associate professor of restorative sciences, Baylor College of Dentistry, Dallas, Tex. d Professor of orthodontics, Baylor College of Dentistry, Dallas, Tex. Reprint requests to: Dr Peter H. Buschang, Department of Orthodontics, Baylor College of Dentistry, Texas A & M University System Health Science Center, 3302 Gaston Ave, Dallas, TX 75246; e-mail, [email protected] Submitted, April 2004; revised and accepted, July 2004. 0889-5406/$30.00 Copyright © 2005 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.07.045 b
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with malocclusions.12 Those with poor dental esthetics have been linked to lack of self-confidence and are thought to be disadvantaged in social, educational, and occupational settings.13,14 During interpersonal interactions, the eyes primarily scan other people’s eyes and mouths, with little time spent on other features.15 Thus it is not surprising that the general public considers the smile to rank second only to the eyes when considering features most important to facial esthetics.3 Despite the importance of dental esthetics, little has been done to understand the contribution of the smile’s components. One such component is tooth shape. Many notions held today on the esthetics of tooth shape are based on authoritative writings aimed at guiding denture tooth selection. For example, Williams16 suggested that tooth shape should be determined by facial form. However, selecting tooth shape on the basis of facial form has not been supported by the literature. In fact, several studies have found no correlation between facial outline and actual or preferred tooth shape.17-19 Other popular methods for selecting tooth shapes in the past were based on stereotypes: women should have round, soft, and delicate teeth (tapering/ovoid); men should have square, angular teeth.20,21 But the validity of these stereotypes in tooth selection was called into question when dentists, dental students, and patients were asked to assess “masculine” and “feminine” tooth arrangements, and all subjects preferred the “masculine” arrangements.2 Thus, many traditional concepts on ideal tooth shape have not withstood the evidencebased litmus test. Because of the limited studies evaluating the esthetics of tooth shape, this study was designed to test the following null hypotheses: (1) a change in maxillary tooth shape will have no effect on
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Table I.
Demographic characteristics of judges Sex
Age (y)
Group
N
Men
Women
Unspecified
21-30
31-40
41-50
51-60
⬎60
Unspecified
Restorative dentists Laypeople Orthodontists
120 102 113
94 21 97
22 80 16
4 1 0
11 19 10
22 24 24
40 41 31
30 11 29
14 5 20
3 2 ⫺1
Fig 1. Survey design. Two booklets contained male smiles and 2 contained female smiles. Photographs were presented randomly, 3 smiles per page for incisor and canine shapes and 5 per page for lateral incisor positions.
esthetic preferences and (2) there will be no differences in esthetic scores between restorative dentists, laypeople, and orthodontists. MATERIAL AND METHODS
Three groups of judges were recruited: restorative dentists, laypeople, and orthodontists (Table I). The restorative dentists included both general dentists and prosthodontists from various Texas dental societies and some part-time restorative faculty in the restorative, prosthodontic, and Advanced Education in Graduate Dentistry programs at Baylor College of Dentistry. Laypeople were selected from consenting persons in the Baylor College of Dentistry waiting room areas. The orthodontic sample was obtained from 3 national orthodontic meetings and part-time faculty at 4 university orthodontic programs. The judges each evaluated 18 color photographs of smiles portrayed in either a male or female booklet (Fig 1). Pages 1-3 tested incisor shape preferences while maintaining canine shape. Pages 4-6 tested canine shape preferences while maintaining incisor shape. The photographs on each page were randomly grouped, and only 1 variable (incisor or canine shape) was tested on each page. The nose and chin were eliminated from the photographs to reduce the number of confounding variables. The female photographs, obtained from the Lorin Library,22 showed 18 unique veneer restorations for the
6 maxillary anterior teeth performed on 1 person. These veneers included 3 shapes based on the incisal line angles of the central and lateral incisors: square, square-round, and round. Three canine shapes were also compared: pointed, round, and flat. The various tooth shapes were evaluated in the same mouth by using try-in paste. Standardized photographs were taken with the Kodak 290 digital camera after placing fresh lipstick and having the patient smile naturally with the upper and lower teeth slightly apart. Figure 2 shows the first page of the female booklet, illustrating square-round incisors with flat canines, square incisors with flat canines, and round incisors with flat canines. The male photographs were created with Digident (Digident.com, Coral Springs, Fla) software. The intraoral photographs of the female patient were morphed onto a single male smile. Figure 3 shows page 4 of the male booklet, evaluating canine preferences with square-round incisors. A visual analog scale (VAS) beside each photograph was used to record the judges’ ratings. Each judge was directed to evaluate only the maxillary teeth and to mark on the VAS beside each photograph. Written instructions explained that the marking along the VAS indicated how attractive they judged the maxillary teeth to be. The center line on the VAS indicated average attractiveness, and marks located to the right or the left indicated progressively more or less
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Fig 2. Female incisor shape with flat canines. Incisor shapes: Sr, square-round; S, square; R, round. Canine shape: F, flat.
American Journal of Orthodontics and Dentofacial Orthopedics October 2005
Fig 3. Male canine shapes with square-round incisors. Incisor shape: Sr, square-round. Canine shapes: P, pointed; F, flat; R, round.
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Table II. Variable Incisors
Female incisor shape preferences of restorative dentists, laypeople, and orthodontists Restorative dentists Mean
Incisors with flat canines Sr 57.1 S 46.6 R 69.1 P ⬍ .05 R ⬎ Sr ⬎ S Incisors with round canines Sr 62.7 S 47.5 R 65.8 P ⬍ .05 R ⬎ S; Sr ⬎ S Incisors with pointed canines Sr 54.7 S 46.2 R 63.0 P ⬍ .05 R ⬎ Sr ⬎ S
Laypeople
Orthodontists
SD
Mean
SD
14.7 17.1 22.8
67.1 66.1 73.7 R⬎S
19.2 19.8 18.0
16.3 17.1 22.1
65.1 65.8 69.4
18.1 17.5 21.9
64.5 64.1 65.6
SD
P
Post-hoc
58.9 47.8 71.2 R ⬎ Sr ⬎ S
16.4 17.0 19.2
.005 ⬍.001 .497
D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L
19.5 19.9 19.5
61.3 51.3 64.4 R ⬎ S; Sr ⬎ S
15.1 17.9 19.7
.513 ⬍.001 .429
21.9 18.9 20.8
61.2 50.7 64.5 R ⬎ S; Sr ⬎ S
17.6 14.7 19.6
.028 ⬍.001 .800
attractive maxillary teeth, respectively. The distance from the left end of the VAS was expressed as a percentage of the total VAS. Judges were also asked to indicate their sex, age category, and race by checking the appropriate boxes, but to make no other identifying marks. A pilot study was conducted to validate the survey instrument. Six experienced orthodontists (10⫹ years experience) and 10 randomly chosen laypeople completed the initial survey instrument and were asked a series of questions designed to determine whether they understood the instructions and what the marks on the VAS meant to them. They were also asked what they thought they were evaluating and whether they evaluated the photographs individually or made comparisons within or across pages. Based on the responses from this pilot study, the instructions were modified to more clearly indicate the sex in the photographs and to specifically instruct the judges to focus their evaluation on the maxillary teeth. The variables were distributed normally based on the skewness and kurtosis statistics. Paired t tests were performed to test for significant differences in preference of tooth shape and lateral incisor position in each group. Because of the differences in sex distributions among groups, a 3-way ANOVA with interaction was performed. The initial analysis consisted of a 3-way ANOVA testing for the effects of sex, age group, professional group, and their interactions. The analyses were performed separately for the male and female photographs. Age was significant in only 2 of the 36 comparisons and was therefore excluded from further analysis. Once age was removed, there was no interaction between the other factors.
Mean
ANOVA differences
D ⬍ L; O ⬍ L
D⬍L D ⬍ L; O ⬍ L
RESULTS
With 1 exception, laypeople did not significantly discriminate between any of the female incisor shapes (Table II). Restorative dentists and orthodontists, on the other hand, preferred round and square-round incisors over square incisors in the female images (P ⬍ .001). In addition, restorative dentists preferred round incisors over square-round incisors (P ⱕ .03) for most of the female dental arrangements. When evaluating male images (Table III), all 3 groups preferred square-round incisors over square incisors (P ⱕ .001). Both professional groups rated square-round incisors significantly more attractive than round incisors (P ⱕ .042) in the male images. Orthodontists also tended to prefer round incisors over square incisor arrangements in the male images (P ⱕ .023). In general, laypeople scored all of the female images (Table II) much higher than the orthodontists and restorative dentists. Differences between laypeople and dental professionals were significant for squareround and square incisor shapes. No significant group differences were found when evaluating round incisors in the female images. However, restorative dentists rated round incisors significantly less attractive than either orthodontists or laypeople when evaluating the male images (Table III). Laypeople did not show a preference in canine arrangement for the female images (Table IV). Restorative dentists and orthodontists rated flat canines as more attractive than round canines with squareround incisors (P ⱕ .002). Both groups also rated the flat canines to be more attractive than pointed canines in the female images with round incisors (P ⱕ
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Table III. Variable Incisors
American Journal of Orthodontics and Dentofacial Orthopedics October 2005
Male incisor shape preferences of restorative dentists, laypeople, and orthodontists Restorative dentists Mean
Incisors with flat canines Sr 58.9 S 50.0 R 52.0 P ⬍ .05 Sr ⬎ R; Sr ⬎ S Incisors with round canines Sr 61.3 S 51.0 R 47.7 P ⬍ .05 Sr ⬎ R; Sr ⬎ S Incisors with pointed canines Sr 60.0 S 50.2 R 48.8 P ⬍ .05 Sr ⬎ R; Sr ⬎ S
Table IV.
Laypeople
Orthodontists
ANOVA differences
SD
Mean
SD
Mean
SD
P
Post-hoc
16.2 18.5 20.0
63.8 53.9 66.1 R ⬎ S; Sr ⬎ S
20.5 20.7 23.1
63.5 52.7 63.5 Sr ⬎ S; R ⬎ S
15.8 18.6 15.8
.234 .545 ⬍.001
D ⬍ L; D ⬍ O
16.1 16.2 21.7
65.3 54.7 56.3 Sr ⬎ R; Sr ⬎ S
18.0 19.9 21.4
66.0 54.3 60.4 Sr ⬎ R ⬎ S
15.2 16.1 15.6
.262 .474 .003
D ⬍ L; D ⬍ O
15.9 17.7 21.4
66.4 56.0 57.7 Sr ⬎ S
20.1 18.1 20.8
66.7 54.4 59.0 Sr ⬎ R; Sr ⬎ S
15.3 17.8 17.6
.07 .222 .014
D ⬍ L; D ⬍ O
Female canine shape preferences of restorative dentists, laypeople, and orthodontists
Variable
Restorative dentists
Canines
Mean
SD
Canines with square-round incisors P 54.9 19.0 F 59.5 16.3 R 53.7 15.8 P ⬍ .05 F⬎R Canines with round incisors P 55.5 19.0 F 63.0 20.0 R 58.3 21.6 P ⬍ .05 F⬎P Canines with square incisors P 44.7 17.0 F 43.2 17.7 R 45.6 20.8 P ⬍ .05
Laypeople Mean
Orthodontists
ANOVA differences
SD
Mean
SD
64.2 67.1 63.8
18.9 18.1 20.3
61.9 57.3 52.8 P ⬎ R; F ⬎ R
18.3 15.4 17.5
.027 .008 .003
62.8 67.9 64.4
19.4 22.3 18.7
61.6 65.7 65.4 F ⬎ P; R ⬎ P
19.0 19.3 17.1
.101 .466 .114
62.7 60.9 64.7
20.6 18.5 20.0
51.0 47.7 48.4 P⬎F
16.5 18.4 17.4
⬍.001 ⬍.001 ⬍.001
.025). Uniquely, orthodontists preferred pointed canines over flat canines with square incisors (P ⫽ .023) and round canines over pointed canines with round incisors (P ⫽ .022) in the female images. Restorative dentists did not make a significant distinction in preferences between canine arrangements in the male images (Table V). Orthodontists rated pointed and round canines significantly more attractive than flat canines when paired with square-round incisors in the male images (P ⱕ .005). Laypeople rated flat canines more attractive than round or pointed canines when paired with round incisors (P ⱕ .041). In addition, laypeople rated the female images significantly more attractive than did restorative
P
Post-hoc D ⬍ L; D ⬍ O D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L
D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L D ⬍ L; O ⬍ L
dentists and orthodontists except for canine shapes associated with round incisors (Table IV). For the male images (Table V), orthodontists rated round incisors with the various canine arrangements significantly more attractive than restorative dentists (P ⱕ .020). Laypeople, on the other hand, rated square incisors with pointed and flat canine shapes significantly more attractive than restorative dentists (P ⱕ .026). In general, male judges tended to be less critical than female judges about female images (Table VI). Male judges rated female images with square-round and round incisors as more attractive than female judges (P ⱕ .04). They also judged flat canines more attractive than female judges (P ⱕ .037).
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Table V.
Male canine shapes preferences of restorative dentists, laypeople, and orthodontists Restorative dentists
Variable Canines
Mean
SD
Canines with square-round incisors P 59.9 16.4 F 55.9 17.8 R 58.7 16.2 P ⬍ .05 Canines with round incisors P 48.5 15.6 F 50.8 15.4 R 48.4 18.3 P ⬍ .05 Canines with square incisors P 47.0 14.5 F 46.5 15.2 R 47.9 15.2 P ⬍ .05
Table VI.
Laypeople
Orthodontists
ANOVA differences
Mean
SD
Mean
SD
P
Post-hoc
65.2 60.8 62.4
20.1 17.6 17.6
65.8 58.1 65.8 P ⬎ F; R ⬎ F
15.7 17.1 14.8
.141 .343 .067
54.3 60.7 54.1 F ⬎ P; F ⬎ R
17.8 17.1 18.0
59.1 59.0 57.6
17.3 17.7 16.5
.004 .005 .021
D⬍O D ⬍ L; D ⬍ O D⬍O
55.3 56.7 56.0
19.2 22.7 23.3
53.3 51.9 52.2
18.6 18.3 17.4
.036 .020 .083
D⬍L D⬍L
Sex differences in female images Variable
Male judges
Female judges
Incisors
Canine
Mean
SE
Mean
SE
P
Sr S R Sr S R Sr S R Sr Sr Sr S S S R R R
F F F R R R P P P P F R P F R P F R
61.2 53 72.3 63.7 54.3 65.6 59.3 52.6 65.5 60.3 61.3 57.9 60 67.3 63.7 50.9 50.6 50.3
2.1 2.3 2.3 2.1 2.2 2.4 2.3 2.1 2.4 2.4 2.1 2.3 2.3 2.5 2.3 2.2 2.2 2.4
54.9 49.4 60.5 56 47.1 58.3 53 48.3 55.2 53.8 55.8 48.3 58.6 56 57.5 46.8 41.3 46.3
3.3 3.6 3.7 3.3 3.6 3.8 3.6 3.3 3.9 3.7 3.3 3.6 3.6 3.9 3.7 3.5 3.5 3.7
.019 NS .003 .041 NS .033 .044 NS .015 NS .026 .006 NS .007 NS NS .037 NS
NS, Not significant.
DISCUSSION
Restorative dentists’ incisor shape preferences appear to be consistent with traditional educational concepts, basing ideal tooth shape on sex stereotypes, which hold that men are thought of as square, angular, and rugged and should have square, more angled teeth, whereas women are soft, round, and delicate and should have more rounded teeth.21,23 For example, round incisors received the highest esthetic scores, and square incisors received the lowest for the female images. For
the male images, restorative dentists liked the squareround incisors the best and the round incisors the least. Orthodontists’ esthetic evaluations deviated from the restorative dentists. Even though they preferred rounded incisal angles for the female incisor shapes (round and square-round), they did not discriminate between them. Orthodontists as a group were more accepting of round incisors on the male images than were the restorative dentists and liked the square incisor arrangement the least.
464 Anderson et al
Laypeople liked all incisor shapes on the female image. However, for males, laypeople liked round incisors combined with flat canines and square-round incisors combined with round and pointed canines. Square incisors were the least preferred for males regardless of the canine shape. When considering function, the canine is all-important,24 but until now, little has been known about its esthetic impact. The results from this study indicate that the shape of the canine is relatively unimportant. All 3 groups seem to have focused on the incisors, devoting little attention to the canines. This might be because the canine makes up a small percentage of relative tooth display compared with the incisors from a front view or because dental professionals’ focus is often placed on canine function23,25 and Angle classification rather than canine shape. There are 2 possible explanations for the group differences regarding female incisor shape. First, there might have been a difference in the groups’ abilities to discriminate differences. Because restorative dentists had a single preference for female incisor shape in this study, one could conclude that they were better able to discriminate between incisor shapes than orthodontists (who liked both round and square-round incisors) and laypeople. Interestingly, Kokich et al26 found that orthodontists are more discriminating than general dentists when evaluating midline deviations and gingiva-to-lip distances. Perhaps the ability to discriminate is associated with familiarity; restorative dentists more often deal with incisor shape, while orthodontists more often deal with the variables tested by Kokich et al.26 Second, it is possible that an actual difference in preferences existed among groups. Brisman2 reported different esthetic preferences among dentists and laypeople when evaluating various shapes and symmetry of unisex maxillary anterior teeth. Interestingly, restorative dentists were even more critical than orthodontists when evaluating round incisors in men. An additional explanation for this difference could be that orthodontists are more accepting of round incisors because they work with more youthful male dentitions (which have less wear) than do the restorative dentists. As previously indicated, possible differences between the dental professionals and laypeople in both this study and that of Brisman2 might be due to educational bias because dentists are trained in tooth selection and to be critical when evaluating the dentition. With these possible explanations, it would be wise to involve the patient in treatment planning, whether it involves incisal-edge recontouring or complete restoration of the anterior dentition. The sex of the judge had a significant impact on the
American Journal of Orthodontics and Dentofacial Orthopedics October 2005
esthetic scores. Male judges clearly rated most of the female images more attractive than the female judges. The reverse trend was present in evaluations of male images, with the female judges tending to be less critical than the male judges. This supports other studies’ findings that people are less critical when evaluating attractiveness in the opposite sex.27,28 CONCLUSIONS
Orthodontists, restorative dentists, and laypeople share more similarities than differences when considering dental esthetic values. However, important differences between these groups were identified. Having a better understanding of these similarities and differences will allow practitioners to design treatment plans that consider the esthetic preferences of both the patient and the dental professional. Moreover, esthetic values can differ greatly among patients. Even though there were no clear preferences for the laypeople as a group, they expressed clear individual preferences. Therefore, treatment must be individualized so that the patient’s unique esthetic preferences can be incorporated.29,30 Based on the results of this study, the following conclusions can be made: 1. Restorative dentists preferred round incisors for the female images. Orthodontists preferred round and square-round incisors for the female images. Laypeople did not express a preference in female incisor shape. 2. All 3 groups preferred square-round incisors for the male images. 3. Canine shape played a less important role than incisor shape in the esthetics of the anterior dentition. 4. Lay people tended to be less critical than dental professionals. Restorative dentists tended to be more critical than both laypeople and orthodontists when evaluating round incisors in male images. 5. Male judges were less critical than female judges when evaluating female images. We thank Drs Lorin Berland for providing the female photographs from the Lorin Library and Amelia Williams and David Traub for their help in imaging the male smiles. REFERENCES 1. Qualtrough A, Burke F. A look at dental esthetics. Quintessence Int 1994;25:7-14. 2. Brisman AS. Esthetics: a comparison of dentists’ and patients’ concepts. J Am Dent Assoc 1980;100:345-52. 3. Goldstein R. Study of need for esthetics in dentistry. J Prosthet Dent 1969;21:589-98.
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4. Peck H, Peck S. A concept of facial esthetics. Angle Orthod 1970;40:284-318. 5. Dion KK, Berscheid E, Walster E. What is beautiful is good. J Pers Soc Psychol 1972;24:285-90. 6. Corter C, Trehub S, Boukydis C. Nurses judgment on attractiveness of premature infants. Infant Behav Dev 1978;1:373-80. 7. Clifford M, Walster E. The effect of physical attractiveness on teacher expectations. Sociol Educ 1973;46:248-58. 8. Clifford M. Physical attractiveness and academic performance. Child Study J 1975;5:201-9. 9. Rich J. Effects of children’s physical attractiveness on teacher’s evaluations. J Ed Res 1975;67:599-609. 10. Adams GR, La Voie JC. The effect of sex of child, conduct, and facial attractiveness on teacher expectancy. Education 1974; 95:76-83. 11. Cash TF, Gillen B, Burns DS. Sexism and “beautyism” in personal consultant decision making. J Appl Phychol 1977;62: 301-10. 12. Shaw WC, Rees G, Dawe M, Charles CR. The influence of dentofacial appearance on social attractiveness of young adults. Am J Orthod 1985;87:21-6. 13. Jenny J, Cons NC, Kohout FJ, Jacobsen JR. Relationship between dental esthetics and attributions of self-confidence [abstract]. J Dent Res 1990;69:204. 14. Adams GR. Physical attractiveness research. Hum Dev 1977;20: 217-39. 15. Miller AG. Role of physical attractiveness in impression formation. Psychol Sci 1970;19:241-43. 16. Williams JL. A new classification of human tooth forms with reference to a new system of artificial teeth. Dent Cosmos 1914;56:627-8.
17. Bell RA. The geometric theory of selection of artificial teeth. J Am Dent Assoc 1978;97:637-40. 18. Seluk L, Brodbelt R, Walker G. A biometric comparison of face shape with denture form. J Oral Rehab 1987;14:139-45. 19. Brodbelt RHW, Walker GF, Nelson D, Seluk LW. A comparison of tooth shape with tooth form. J Prosthet Dent 1984;52:588-92. 20. Marunick MT, Chamberlain BB, Robison CA. Denture esthetics: an evaluation of layman’s preferences. J Oral Rehab 1983;10: 399-406. 21. Frush JP, Fisher RD. Introduction to dentogenic restoration. J Prosthet Dent 1955;5:586-95. 22. Berland L, Traub DL. The Lorin Library smile selection workbook. 2001.Digident.com; Coral Springs: 23. Johnson DL, Stratton RJ. Fundamentals of removable prosthodontics. 1988. Quintessence; Chicago: p. 289 –305. 24. Okeson JP. Management of temporomandibular disorders and occlusion. 4th ed 1998. Mosby; Saint Louis: p. 120. 25. Ash MM. Wheeler’s dental anatomy, physiology, and occlusion. 6th ed1984. W. B. Saunders; . Philadelphia: p. 154 –75. 26. Kokich VO, Kiyak HA, Shapiro PA. Comparing the perceptions of dentists and laypeople to altered dental esthetics. J Esthet Dent 1999;11:311-24. 27. Tennis GH, Dabbs JM. Judging physical attractiveness: effects of judges’ own attractiveness. Pers Soc Psychol Bulletin 1975;1: 513-6. 28. Lerner RM, Karabenick SA. Physical attractiveness, body attitudes, and self-concept in late adolescents. J Youth Adoles 1974;23:307-16. 29. Chalifoux PR. Practice made perfect; perception esthetics: factors that affect smile design. J Esthet Dent 1996;8:189-92. 30. Peck S, Peck L. Selected aspects of the art and science of facial esthetics. Semin Orthod 1995;1:105-26.
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