Abstract
Background:
A smile is defined as a universal welcome. The perception of smile attractiveness is affected by the persons' social background and their own experiences. The existing literature states that orthodontists, restorative dentists, and laypersons have different opinions.
Aims:
The aim of this study is to compare the perception of orthodontists, restorative dentists, and laypersons regarding smile esthetics.
Materials and Methods:
A survey-based study was conducted. The target population was orthodontists, restorative dentists, and laypersons in Saudi Arabia. An electronic survey that included digitally altered photographs representing different smile parameters was designed by an Adobe Photoshop Certified Expert. Participants were asked to choose the most attractive smile in each question.
Results:
Unilateral changes in the width or length of the central incisors were the least attractive among the three groups. About 38%, 48%, and 41% of the participating orthodontics, restorative dentists, and laypersons, respectively, found that wider buccal corridors were more attractive. Moreover, 27% of the laypersons found the reversed smile arc to be attractive.
Conclusion:
The tolerance level in evaluating the asymmetry and the width of the buccal corridors was similar for the three groups. Laypersons were less sensitive to the deviations from the ideal in the smile arc and the amount of lower lip coverage of the incisors.
Clinical Significance:
Understanding the differences in the perception of smile attractiveness among orthodontists, restorative dentists and laypersons will undoubtedly be beneficial in diagnosis, setting treatment objectives and treatment planning.
Key words: Buccal corridors, gingival display, laypersons, orthodontists, restorative dentists, smile arc, smile attractiveness, smile features
INTRODUCTION
A smile is defined as a universal welcome. In the past, the parameters determining the attractiveness of a smile were based only on authors' opinions. Nowadays, the concept of beauty is subjective and is considerably influenced by other people's opinions. Evidence-based literature plays a tremendous role in developing this concept, and beauty standards and the variation of what some can find attractive and others do not has been proven to be primarily influenced by uncontrollable factors such as cultural differences.[1] The perception of smile attractiveness, in particular, is also affected by the persons' social background and their own experiences.[2] Dental features such as symmetry, width of buccal corridors, and smile arc can improve or compromise the attractiveness of a smile and thus, should be carefully controlled during esthetic diagnosis and treatment planning.[3] Symmetry is expressed not only in terms of the size and width of teeth but also in terms of the position of the upper and lower dental midlines.[4] As suggested by Frush and Fisher, the width of the buccal corridors is an essential factor in expressing the naturalism of a smile. They also indicated that in the evaluation of the smile arc, a harmonious relationship between the incisal edges of the upper incisors along with the canines and the curvature of the lower lip is required.[5] Previous studies have revealed that orthodontists, general practitioners, and laypersons have different opinions when it comes to their perception of smile attractiveness.[6,7] Moreover, the general public is less sensitive to minor deviations from the ideal parameters.[8]
Aims
The aim of this study was to determine and compare the perception of orthodontists, restorative dentists, and laypersons regarding smile esthetics and attractiveness and to determine the difference in the esthetic standards among the three groups.
MATERIALS AND METHODS
A survey-based study was conducted. The target population consisted of orthodontists, restorative dentists, and laypersons in Saudi Arabia. In the initial stage, an electronic survey that included digitally altered photographs representing different smile parameters was designed by an Adobe Photoshop cc 2018 by Adobe Inc, San jose, California, U.S.A Certified Expert [Figures 1–9]. The survey link was distributed electronically through emails and social media servers, and some orthodontists and restorative dentists were personally contacted to participate in the survey. The first section included demographic questions pertaining to the age, gender, and profession of the participants. In the following section, nine questions were included; the participants were asked to choose the most attractive smile from the three options of photographs provided in each question. The unaltered photograph was considered the ideal smile. The options in each question were randomly arranged by an investigator different from the one who collected the data and the one who interpreted the results in order to minimize the chances of a bias. A statistical analysis was carried out using the Statistical Package for the Social Sciences (SPSS) version 25 by IBM New York, U.S.A. program.
Figure 1.
Distribution of altered photograph options in Q1. (a) Width of central incisors has been increased by 1–2 mm bilaterally, (b) width of central incisor has been increased by 1–2 mm unilaterally, (c) unaltered photograph
Figure 9.
Distribution of altered photograph options in Q9. (a) Lower midline shift by 2 mm to the lift in relation to the upper midline, (b) unaltered photograph, (c) lower midline shift by 1 mm to the lift in relation to the upper midline
Figure 2.
Distribution of altered photograph options in Q2. (a) Unaltered photograph, (b) width of central incisor has been decreased by 1–2 mm unilateral, (c) width of central incisors has been decreased by 1–2 mm bilaterally
Figure 3.
Distribution of altered photograph options in Q3. (a) Length of central incisors has been increased by 1–2 mm bilaterally, (b) unaltered photograph, (c) length of central incisor has been increased by 1–2 mm unilaterally
Figure 4.
Distribution of altered photograph options in Q4. (a) Unaltered photograph, (b) length of central incisor has been decreased by 1–2 mm unilateral, (c) length of central incisors has been decreased by 1–2 mm bilaterally
Figure 5.
Distribution of altered photograph options in Q5. (a) Represent narrow buccal corridors (showing up to the distal surface of the first premolar), (b) unaltered photograph, (c) narrow buccal corridors (showing only up to the mesial surface of the second premolar
Figure 6.
Distribution of altered photograph options in Q6. (a) Around 0 mm of gingival display upon smiling, (b) around <3 mm of gingival display upon smiling, (c) unaltered photograph
Figure 7.
Distribution of altered photograph options in Q7. (a) The curvature of the lower lip is covering around 1 mm of upper anterior teeth upon smiling, (b) unaltered photograph, (c) the curvature of the lower lip is covering around >1 mm of upper anterior teeth upon smiling
Figure 8.
Distribution of altered photograph options in Q8. (a) Reversed smile arc, (b) straight smile arc, (c) unaltered photograph
Table 1 represent the distribution of original and modifies smile photographs based on multiple smile parameter question in the same pattern as the were presented in the survay.
Table 1.
Distribution of altered photographs options in the survey
| Smile parameter | First option | Second option | Third option |
|---|---|---|---|
| Mesiodistal width | Bilateral increase in width of central incisors by 1-2 mm | Unilateral increase in width of central incisors by 1-2 mm | Unaltered photograph |
| Mesiodistal width | Unaltered photograph | Unilateral decrease in the width of central incisors by 1-2 mm | Bilateral decrease in the width of central incisors by 1-2 mm |
| Gingivoincisal length | Bilateral increase in length of central incisors by 1-2 mm | Unaltered photograph | Unilateral increase in length of central incisors by 1-2 mm |
| Gingivoincisal length | Unaltered photograph | Unilateral decrease in length of central incisors by 1-2 mm | Bilateral decrease in length of central incisors by 1-2 mm |
| Width of buccal corridors | Narrow buccal corridors (showing up to the distal surface of the first premolar) | Unaltered photograph | Narrow buccal corridors (showing only up to the mesial surface of the second premolar) |
| Amount gingival display | 0 mm of gingival display | <3 mm gingival display | Unaltered photograph |
| Distance between lower lip and the tip of upper anterior teeth | Lower lip covering 1 mm of the upper anterior teeth | Unaltered photograph | Lower lip covering >1 mm of the upper anterior teeth |
| Smile arc | Reversed smile arc | Straight smile arc | Unaltered photograph |
| Position of lower midline in relation to the upper midline | Lower midline shifted by 2 mm in relation to the upper midline | Unaltered photograph | Lower midline shifted by 1 mm in relation to the upper midline |
RESULTS
In all, 244 participants responded to this survey. Table 2 shows the demographic characteristics of the participants. Table 3 shows the participants' perception of smile attractiveness. Overall, a majority of the participants chose the unaltered photograph for Q1 (n = 182, 74.6%), Q3 (n = 214, 87.7%), Q6 (n = 205, 84.0%), Q7 (n = 186, 76.2%), and Q8 (n = 150, 61.5%).
Table 2.
Demographics
| Frequency, n (%) | |
|---|---|
| Gender | |
| Male | 116 (47.5) |
| Female | 128 (52.5) |
| Profession | |
| Restorative dentist | 76 (31.1) |
| Orthodontist | 69 (28.3) |
| Layperson | 99 (40.6) |
Table 3.
Perception of the smile attractiveness
| Frequency, n (%) | ||
|---|---|---|
| Q1 | Bilateral increase in width of central incisors by 1-2 mm | 33 (13.5) |
| Unilateral increase in width of central incisors by 1-2 mm | 29 (11.9) | |
| Unaltered photograph | 182 (74.6) | |
| Q2 | Unaltered photograph | 90 (36.9) |
| Unilateral decrease in the width of central incisors by 1-2 mm | 84 (34.4) | |
| Bilateral decrease in the width of central incisors by 1-2 mm | 70 (28.7) | |
| Q3 | Bilateral increase in length of central incisors by 1-2 mm | 19 (7.8) |
| Unaltered photograph | 214 (87.7) | |
| Unilateral increase in length of central incisors by 1-2 mm | 11 (4.5) | |
| Q4 | Unaltered photograph | 130 (53.3) |
| Unilateral decrease in length of central incisors by 1-2 mm | 24 (9.8) | |
| Bilateral decrease in length of central incisors by 1-2 mm | 90 (36.9) | |
| Q5 | Narrow buccal corridors (showing up to the distal surface of first premolar) | 44 (18.0) |
| Unaltered photograph | 127 (52.0) | |
| Narrow buccal corridors (showing only up to the mesial surface of second premolar) | 73 (30.0) | |
| Q6 | 0 mm of gingival display | 20 (8.2) |
| <3 mm gingival display | 19 (7.8) | |
| Unaltered photograph | 205 (84.0) | |
| Q7 | Lower lip covering 1 mm of the upper anterior teeth | 24 (9.8) |
| Unaltered photograph | 186 (76.2) | |
| Lower lip covering>1 mm of the upper anterior teeth | 34 (13.9) | |
| Q8 | Reversed smile arc | 34 (13.9) |
| Straight smile arc | 60 (24.6) | |
| Unaltered photograph | 150 (61.5) | |
| Q9 | Lower midline shifted by 2 mm in relation to the upper midline | 49 (20.1) |
| Unaltered photograph | 119 (48.8) | |
| Lower midline shifted by 1 mm in relation to the upper midline | 76 (31.1) |
Association between perception of smile attractiveness and gender
Table 4 shows the association between the perception of smile attractiveness and gender. The two-way cross-tabulation revealed that males were more likely to choose the unaltered photograph for Q1, Q2, Q4, Q5, and Q6 than females. Females were more likely to choose the unaltered photograph for Q3, Q7, Q8, and Q9 than males. However, the Chi-square test showed no statistically significant association (P > 0.05).
Table 4.
Perception of the smile attractiveness by gender
| Gender, n (%) | P | |||
|---|---|---|---|---|
| Male | Female | |||
| Q1 | Bilateral increase in width of central incisors by 1-2 mm | 15 (12.9) | 18 (14.1) | 0.497 |
| Unilateral increase in width of central incisors by 1-2 mm | 11 (9.5) | 18 (14.1) | ||
| Unaltered photograph | 90 (77.6) | 92 (71.9) | ||
| Q2 | Unaltered photograph | 47 (40.5) | 43 (33.6) | 0.523 |
| Unilateral decrease in the width of central incisors by 1-2 mm | 37 (31.9) | 47 (36.7) | ||
| Bilateral decrease in the width of central incisors by 1-2 mm | 32 (27.6) | 38 (29.7) | ||
| Q3 | Bilateral increase in length of central incisors by 1-2 mm | 11 (9.5) | 8 (6.3) | 0.556 |
| Unaltered photograph | 99 (85.3) | 115 (89.8) | ||
| Unilateral increase in length of central incisors by 1-2 mm | 6 (5.2) | 5 (3.9) | ||
| Q4 | Unaltered photograph | 63 (54.3) | 67 (52.3) | 0.332 |
| Unilateral decrease in length of central incisors by 1-2 mm | 8 (6.9) | 16 (12.5) | ||
| Bilateral decrease in length of central incisors by 1-2 mm | 45 (38.8) | 45 (35.2) | ||
| Q5 | Narrow buccal corridors (showing up to the distal surface of first premolar) | 18 (15.5) | 26 (20.3) | 0.607 |
| Unaltered photograph | 63 (54.3) | 64 (50.0) | ||
| Narrow buccal corridors (showing only up to the mesial surface of second premolar) | 35 (30.2) | 38 (29.7) | ||
| Q6 | 0 mm of gingival display | 7 (6.0) | 13 (10.2) | 0.353 |
| <3 mm gingival display | 11 (9.5) | 8 (6.3) | ||
| Unaltered photograph | 98 (84.5) | 107 (83.6) | ||
| Q7 | Lower lip covering 1 mm of the upper anterior teeth | 14 (12.1) | 10 (7.8) | 0.154 |
| Unaltered photograph | 82 (70.7) | 104 (81.3) | ||
| Lower lip covering >1 mm of the upper anterior teeth | 20 (17.2) | 14 (10.9) | ||
| Q8 | Reversed smile arc | 18 (15.5) | 16 (12.5) | 0.685 |
| Straight smile arc | 30 (25.9) | 30 (23.4) | ||
| Unaltered photograph | 68 (58.6) | 82 (64.1) | ||
| Q9 | Lower midline shifted by 2 mm in relation to the upper midline | 27 (23.3) | 22 (17.2) | 0.393 |
| Unaltered photograph | 52 (44.8) | 67 (52.3) | ||
| Lower midline shifted by 1 mm in relation to the upper midline | 37 (31.9) | 39 (30.5) | ||
Association between perception of smile attractiveness and profession
Table 5 shows the association between the perception of smile attractiveness and profession. The two-way cross-tabulation revealed that restorative dentists were more likely to choose the unaltered photograph for Q4, Q5, Q7, and Q8 than orthodontists and laypersons. Orthodontists were more likely to choose the ideal for Q2, Q3, Q6, and Q9 than restorative dentists and laypersons. The Chi-square and Fisher's exact tests showed a statistically significant association between the responses to Q3, Q5, Q6, Q7, and Q8 and the participants' profession (P < 0.05).
Table 5.
Perception of the smile attractiveness by profession
| Profession, n (%) | P | ||||
|---|---|---|---|---|---|
| Restorative dentist | Orthodontist | Layperson | |||
| Q1 | Bilateral increase in width of central incisors by 1-2 mm | 8 (10.5) | 12 (17.4) | 13 (13.1) | 0.061 |
| Unilateral increase in width of central incisors by 1-2 mm | 4 (5.3) | 7 (10.1) | 18 (18.2) | ||
| Unaltered photograph | 64 (84.2) | 50 (72.5) | 68 (68.7) | ||
| Q2 | Unaltered photograph | 25 (32.9) | 29 (42.0) | 36 (36.4) | 0.103 |
| Unilateral decrease in the width of central incisors by 1-2 mm | 30 (39.5) | 27 (39.1) | 27 (27.3) | ||
| Bilateral decrease in the width of central incisors by 1-2 mm | 21 (27.6) | 13 (18.8) | 36 (36.4) | ||
| Q3 | Bilateral increase in length of central incisors by 1-2 mm | 4 (5.3) | 4 (5.8) | 11 (11.1) | 0.002* |
| Unaltered photograph | 71 (93.4) | 65 (94.2) | 78 (78.8) | ||
| Unilateral increase in length of central incisors by 1-2 mm | 1 (1.3) | 0 (0.0) | 10 (10.1) | ||
| Q4 | Unaltered photograph | 44 (57.9) | 36 (52.2) | 50 (50.5) | 0.472 |
| Unilateral decrease in length of central incisors by 1-2 mm | 9 (11.8) | 4 (5.8) | 11 (11.1) | ||
| Bilateral decrease in length of central incisors by 1-2 mm | 23 (30.3) | 29 (42.0) | 38 (38.4) | ||
| Q5 | Narrow buccal corridors (showing up to the distal surface of first premolar) | 9 (11.8) | 15 (21.7) | 20 (20.2) | 0.033* |
| Unaltered photograph | 48 (63.2) | 38 (55.1) | 41 (41.4) | ||
| Narrow buccal corridors (showing only up to the mesial surface of second premolar) | 19 (25.0) | 16 (23.2) | 38 (38.4) | ||
| Q6 | 0 mm of gingival display | 1 (1.3) | 1 (1.4) | 18 (18.2) | 0.000* |
| <3 mm gingival display | 4 (5.3) | 0 (0.0) | 15 (15.2) | ||
| Unaltered photograph | 71 (93.4) | 68 (98.6) | 66 (66.7) | ||
| Q7 | Lower lip covering 1 mm of the upper anterior teeth | 4 (5.3) | 1 (1.4) | 19 (19.2) | 0.000* |
| Unaltered photograph | 65 (85.5) | 59 (85.5) | 62 (62.6) | ||
| Lower lip covering >1 mm of the upper anterior teeth | 7 (9.2) | 9 (13.0) | 18 (18.2) | ||
| Q8 | Reversed smile arc | 3 (3.9) | 4 (5.8) | 27 (27.3) | 0.000* |
| Straight smile arc | 20 (26.3) | 22 (31.9) | 18 (18.2) | ||
| Unaltered photograph | 53 (69.7) | 43 (62.3) | 54 (54.5) | ||
| Q9 | Lower midline shifted by 2 mm in relation to the upper midline | 19 (25.0) | 12 (17.4) | 18 (18.2) | 0.468 |
| Unaltered photograph | 33 (43.4) | 39 (56.5) | 47 (47.5) | ||
| Lower midline shifted by 1 mm in relation to the upper midline | 24 (31.6) | 18 (26.1) | 34 (34.3) | ||
*Statistically significant
DISCUSSION
This study demonstrated that unilateral changes in the width or length of the central incisors were the least attractive among the three groups. Thus, we concluded that symmetry played a major role in improving the attractiveness of a smile. This finding was in accordance with the findings reported by Betrine Ribeiro et al., suggesting that incisal asymmetry compromises esthetics.[9]
Most of the participating orthodontists, restorative dentists, and laypersons found that wider buccal corridors (showing up to the mesial surface of the first molar but not completely obliterated) were more attractive as 38%, 48%, and 41%, respectively, selected the second photograph. This result highlighted the fact that the width of the buccal corridors was directly proportional to the improvement in the smile esthetics, while taking into consideration the avoidance of complete obliteration. Nascimento et al. and Krishnan et al. similarly suggested that intermediate-width buccal corridors are more esthetic and wide obliterated buccal corridors are less pleasant.[10]
With respect to the amount of gingival display that determined the attractiveness of one smile as compared to that of another, most of the participants from the three groups agreed that 1–2 mm of gingival display was the most pleasant range, as 68%, 71%, and 66% of the participating orthodontists, restorative dentists, and laypersons, respectively, selected the unaltered photograph. Moreover, around 18% of the laypersons thought that a 0-mm gingival display was more attractive, where only 1% of the orthodontists and restorative dentists agreed with these laypersons.
A similar conclusion was drawn by Suzuki et al., suggesting that up to 3 mm of gingival exposure upon smiling was acceptable.[11] These results also corroborated the conclusions of two other studies conducted by Kokich et al. in 1999 and 2006, demonstrating that the maximum tolerable amount of gingival show is 3 mm.[12,13] The possible reason for this finding could be the youthful appearance that a gingival display provides.
In the present study, 59%, 65%, and 62% of the participating orthodontists, restorative dentists, and laypersons, respectively, agreed that when the lower lip slightly touched the tip of the upper anterior teeth, the attractiveness of the smile increased. In contrast, 19% and 18% of the laypersons found that a 1-mm coverage of the upper anterior teeth by the lower lip and a >1-mm coverage of the upper anterior teeth by the lower lip were the most attractive, respectively. These findings suggested that the lower lip coverage of the upper incisors was more tolerable in the perception of the laypersons than in that of the orthodontists and the restorative dentists.
An ideal smile arc is found when the lower lip slightly touches the incisal edge without complete coverage.[14,15] The importance of the curvature of the smile arc lies primarily in juvenility, as reported in a previous study by Viga and Brundo in 1978, claiming that the flatter the smile arc is, the less youthful is the smile.[16] Similar results were obtained when the smile arc was evaluated in the present study: 54%, 53%, and 43% of the participating orthodontists, restorative dentists, and laypersons, respectively, reported that a consonant smile arc was the most attractive. However, around 27% of the laypersons found the reversed smile arc to be attractive, which proved that the feature of smile arc was more critical in the perception of restorative dentists and orthodontists than in that of the general public. This was also consistent with the previous findings reported by Saffarpour et al. who indicated that a reversed smile arc was esthetically more acceptable to layperson standards.[17]
The detection of the midline shift was challenging, as the photographs were used to evaluate how successful the three groups were in detecting lower dental deviations. Further, we found that around 39%, 32%, and 47% of the participating orthodontists, restorative dentists, and laypersons, respectively, agreed that a smile became attractive in the absence of lower midline deviations. In addition, note that 18%, 24%, and 34% of the participating orthodontists, restorative dentists, and laypersons, respectively, were not very successful in detecting a 1-mm lower midline shift as they selected the third photograph option. Considering the above results, we concluded that a lower dental midline shift of 1 mm could be overlooked. A similar conclusion was reached by Kokich et al., claiming that the threshold of the midline shift was 1 mm among dental practitioners.[12] Beyer and Lindauer also reported that a 2-mm midline shift was detectable by almost everyone.[18] Controversially, Pinho et al. suggested a difference between the tolerance level of orthodontists and prosthodontists as the former could detect a 1-mm midline shift and the latter only detected the shift when it was 3 mm.[7] The results of the present study contradicted these findings as no statistically significant difference was observed in the tolerance level of the orthodontists and restorative dentists.
CONCLUSION
Within the limitations of this study, we concluded that the tolerance level for evaluating asymmetry and the width of the buccal corridors was similar for the three groups. Laypersons were less sensitive to deviations from the ideal in the smile arc and the amount of lower lip coverage of the incisors. Most of the participants in the three groups found a smile to be more pleasant when the lower midline was centered; however, a 1-mm midline shift was considered acceptable as around one-third of the sample population was not successful in detecting such a shift. Therefore, we highly recommend that clinicians consider the differences in the perceptions of a smile while formulating a treatment plan and setting the treatment objectives to ensure optimal patient benefits and satisfaction.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Abu Alhaija ES, Al-Nimri KS, Al-Khateeb SN. Self-perception of malocclusion among North Jordanian school children. Eur J Orthod. 2005;27:292–5. doi: 10.1093/ejo/cjh094. [DOI] [PubMed] [Google Scholar]
- 2.Flores-Mir C, Silva E, Barriga MI, Lagravere MO, Major PW. Lay person's perception of smile aesthetics in dental and facial views. J Orthod. 2004;31:204–9. doi: 10.1179/146531204225022416. [DOI] [PubMed] [Google Scholar]
- 3.Rodrigues Cde D, Magnani R, Machado MS, Oliveira OB. The perception of smile attractiveness. Angle Orthod. 2009;79:634–9. doi: 10.2319/030508-131.1. [DOI] [PubMed] [Google Scholar]
- 4.Brisman AS. Esthetics: A comparison of dentists' and patients' concepts. J Am Dent Assoc. 1980;100:345–52. doi: 10.14219/jada.archive.1980.0093. [DOI] [PubMed] [Google Scholar]
- 5.Frush J, Fisher R. The dynesthetic interpretation of the dentogenic concept. J Prosthet Dent. 1958;8:558–81. [Google Scholar]
- 6.Roden-Johnson D, Gallerano R, English J. The effects of buccal corridor spaces and arch form on smile esthetics. Am J Orthod Dentofacial Orthop. 2005;127:343–50. doi: 10.1016/j.ajodo.2004.02.013. [DOI] [PubMed] [Google Scholar]
- 7.Pinho S, Ciriaco C, Faber J, Lenza MA. Impact of dental asymmetries on the perception of smile esthetics. Am J Orthod Dentofacial Orthop. 2007;132:748–53. doi: 10.1016/j.ajodo.2006.01.039. [DOI] [PubMed] [Google Scholar]
- 8.Machado AW, McComb RW, Moon W, Gandini LG., Jr Influence of the vertical position of maxillary central incisors on the perception of smile esthetics among orthodontists and laypersons. J Esthet Restor Dent. 2013;25:392–401. doi: 10.1111/jerd.12054. [DOI] [PubMed] [Google Scholar]
- 9.Betrine Ribeiro J, Alecrim Figueiredo B, Wilson Machado A. Does the presence of unilateral maxillary incisor edge asymmetries influence the perception of smile esthetics? J Esthet Restor Dent. 2017;29:291–7. doi: 10.1111/jerd.12305. [DOI] [PubMed] [Google Scholar]
- 10.Nascimento D, Santos Ê, Machado A, Bittencourt M. Influence of buccal corridor dimension on smile esthetics. Dent Press J Orthod. 2012;17:145–50. [Google Scholar]
- 11.Suzuki L, Machado A, Bittencourt M. An evaluation of the influence of gingival display level in the smile esthetics. Dent Press J Orthod. 2011;16:37–9. [Google Scholar]
- 12.Kokich VO, Jr, Kiyak HA, Shapiro PA. Comparing the perception of dentists and lay people to altered dental esthetics. J Esthet Dent. 1999;11:311–24. doi: 10.1111/j.1708-8240.1999.tb00414.x. [DOI] [PubMed] [Google Scholar]
- 13.Kokich VO, Kokich VG, Kiyak HA. Perceptions of dental professionals and laypersons to altered dental esthetics: Asymmetric and symmetric situations. Am J Orthod Dentofacial Orthop. 2006;130:141–51. doi: 10.1016/j.ajodo.2006.04.017. [DOI] [PubMed] [Google Scholar]
- 14.Tjan AH, Miller GD, The JG. Some esthetic factors in a smile. J Prosthet Dent. 1984;51:24–8. doi: 10.1016/s0022-3913(84)80097-9. [DOI] [PubMed] [Google Scholar]
- 15.Lin C. Fundamentals of esthetics. J Dent. 1992;20:244. [Google Scholar]
- 16.Vig RG, Brundo GC. The kinetics of anterior tooth display. J Prosthet Dent. 1978;39:502–4. doi: 10.1016/s0022-3913(78)80179-6. [DOI] [PubMed] [Google Scholar]
- 17.Saffarpour A, Ghavam M, Saffarpour A, Dayani R, Fard MJ. Perception of laypeople and dental professionals of smile esthetics. J Dent (Tehran) 2016;13:85–91. [PMC free article] [PubMed] [Google Scholar]
- 18.Beyer JW, Lindauer SJ. Evaluation of dental midline position. Semin Orthod. 1998;4:146–52. doi: 10.1016/s1073-8746(98)80016-9. [DOI] [PubMed] [Google Scholar]