Influence of maxillary canine gingival margin asymmetries on the perception of smile esthetics among...

ORIGINAL ARTICLE

Influence of maxillary canine gingival marginasymmetries on the perception of smile estheticsamong orthodontists and laypersons

Bruna Dieder Correa,a Marcos Alan Vieira Bittencourt,b and Andre Wilson Machadoc

Salvador, Bahia, Brazil

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Introduction: Our objective was to determine the perception of smile esthetics among orthodontists andlaypeople with respect to asymmetries in the maxillary canines' gingival margins in full-face and close-upsmile analyses. Methods: Full-face and close-up photographs of the frontal smiles of 4 subjects (2 women, 2men) were used. The images were digitally altered to create a symmetrical image with the gingival marginlevels of the maxillary canines matching the central incisors. From this new image, 5 stages of alterationswere made in the gingival margin of the right canine in 0.5-mm increments. Final full-face and close-upimages of the smiles were assessed by 50 orthodontists and 50 laypeople, who indicated the level ofattractiveness of each smile on visual analog scales. The data collected were statistically analyzed by meansof 1-way analysis of variance with the Tukey post-hoc test and the unpaired Student t test. Results: In general,the most attractive smiles for the orthodontists were those without asymmetries and the one with a 0.5-mmasymmetry, whereas laypersons could not detect an asymmetry up to 1.5 mm (P\0.05). For both groups ofraters, the lowest scores were assigned for the smiles with asymmetries of 2.0 and 2.5 mm (P\0.05). Whenopinions of orthodontists and laypersons were compared, in most situations a statistically significantdifference was found, with orthodontists more sensitive in detecting deviations (P \0.001). Moreover, therewas no significant difference (P .0.05) between the full-face and close-up assessments of the smiles.Conclusions: It can be concluded that the perceptions of unilateral asymmetries in the gingival margin levelsof the maxillary canines were 1.0 mm for orthodontists and 1.5 to 2.0 mm for laypersons. (Am J OrthodDentofacial Orthop 2014;145:55-63)

In recent years, facial esthetics has become a majorfocus for the public worldwide. Having a beautiful,youthful smile is among patients' main concerns,

and esthetic improvements are routinely requested indental offices. For this reason, orthodontists worldwideare working hard to incorporate into their clinical routinedifferent tools to focus on improving smile esthetics.1,2

An esthetically pleasing smile should include aspectssuch as symmetry and proportion between the centralincisors,1,3,4 minimal gingival display,5,6 moderate to

the Section of Orthodontics, Dental School, Federal University of Bahia,or, Bahia, Brazil.ent.ram director.ciate professor.thors have completed and submitted the ICMJE Form for Disclosure of Po-l Conflicts of Interest, and none were reported.ss correspondence to: Andre Wilson Machado, Av. Araujo Pinho, 62, 7, Canela, Salvador/BA - Brazil, CEP. 40.110-150; e-mail, [email protected], July 2013; revised and accepted, September 2013.5406/$36.00ight � 2014 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2013.09.010

minimum buccal corridor spaces,7,8 ideal smile arc withthe curvature of the maxillary anterior incisal edgesparallel to the lower lip,9-12 and adequate design ofthe gingival margins in the esthetic zone.5,9-13

With these considerations, studies have evaluatedthe perception of asymmetries in smile esthetics. Ko-kich et al14 conducted a study to evaluate the estheticperceptions of general dentists, orthodontists, andlaypersons regarding alterations in crown lengths ofthe maxillary central incisors and gingival margins ofthe maxillary lateral incisors. With regard to the crownsize of the central incisors, they concluded that ortho-dontists could perceive a 1-mm discrepancy and thatgeneral dentists identified 1.5 mm, but the discrep-ancy was noticeable by laypersons only when thealteration was above 2 mm. In another study, Kokichet al15 investigated this aspect again using asymmetricincrements and concluded that orthodontists weremore sensitive and could detect a 0.5-mm discrep-ancy. General dentists and laypeople were lessrigorous, and they only perceived alterations of 1.5and 2 mm, respectively.

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56 Correa, Vieira Bittencourt, and Machado

An interesting aspect is that in these studies, only thecentral and lateral incisors were assessed.14,15 It isdebatable whether these data can be applied to thecanines. Pinho et al16 investigated the perceptions ofincisal-edge asymmetries between maxillary caninesand found that discrepancies up to 2 mm were not de-tected by orthodontists, prosthodontists, and laypeople.On the other hand, we found no studies that consideredthe perception of smile esthetics with respect to gingivalmargin discrepancies between the maxillary canines.This information is of paramount importance becausethis is a common clinical finding.17 The establishmentof this parameter is critical in some situations such ascanine substitution cases where premolars substituteas canines. In these situations, a gingival asymmetrywill be present, and some authors suggest dental intru-sion followed by restoration to match the gingivalmargin level from the contralateral canine.3,18,19 Thisstrategy might be questionable because if thoseasymmetries cannot be detected, it might beunnecessary to treat them.

Thus, does this discrepancy need to be corrected? Inother words, if laypersons cannot recognize dental orgingival asymmetries as unesthetic, why should they betreated? Would the correction of some gingival discrep-ancies be an overtreatment more than an esthetic need?

Therefore, the aim of this study was to determine theperceptions of smile esthetics among orthodontists andlaypeople with respect to asymmetries in the maxillarycanines' gingival margins in facial and close-up smileanalyses. The null hypothesis was that these asymmetrieswould be rated as attractive equally by orthodontists andlaypeople.

MATERIAL AND METHODS

The study was approved by the research ethics com-mittee of the Dental School, Federal University ofBahia in Brazil, under report number 24/12 and regis-tered at CONEP: CAAE 03798512.9.0000.5024. All par-ticipants in the study signed a form of free andinformed consent.

The sample size was determined using a pilot studyand the Student unpaired t test with 80% power and abilateral alpha level of 5%. It was determined that thesample should include at least 49 persons in each groupof examiners.

Forty-eight images—24 full-face views and 24close-up views—of the smile were used from 4 subjects,who were volunteer patients in the Section of Ortho-dontics at the Federal University of Bahia; the 2 womenand 2 men were white, between 25 and 35 years ofage, with no apparent facial asymmetries, and with

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attractive smiles. These smiles followed some principlesof an ideal smile described in the literature: adequatewidth-to-length proportion of the esthetic zone, sym-metry between maxillary central incisors, convex smilearc, gingival display less than 1.0 mm, and moderatebuccal corridors.3-6,10-13

The photographs were taken by the same operator(B.D.C.) using the digital Rebel camera with an MR-14EX ring flash and a 100-mm macro lens (Canon, To-kyo, Japan) mounted on a tripod.

The selected images were digitally altered using Pho-toshop (CS5.1; Adobe Photoshop, San Jose, Calif). Thephotos were altered to produce symmetrical images andretouched to adjust color, brightness, and contrast, aswell as to remove any discolorations on the lips andskin.1,7,8,16,20-22 Each image was then condensed toachieve an image with measurements identical to thoseon the actual patient. Thus, for the close-up images,each millimeter measured on the digital and printed im-ages was equivalent to eachmillimetermeasured clinicallyon the patient, with the maxillary central incisor as thereference.1,20-22 For the full-face images, the magnifica-tion ratio was 1:2; ie, 1 mm on the printed image wasequivalent to 2 mm in the real patient.

The gingival line of the central incisors was used as areference, and the canines' gingival margins werematched with this line, with the lateral incisor 0.5 mmbelow and an incisal step of 1 mm between the centraland lateral incisors. All mandibular teeth were removedfrom the images.

After these procedures, 5 alterations were created inthe gingival margins of the canines on 1 side, with dis-crepancies of 0.5, 1, 1.5, 2, and 2.5 mm in relation totheir contralateral teeth. Therefore, 6 images were pro-duced for each subject. The upper limit of the full-faceimage (Figs 1 and 2) was the region just above the topof the head, and the lower limit was the base of theneck. The upper limit of the close-up image of the smile(Figs 3 and 4) was the base of the nose, and the lowerlimit was above the chin.

The final images were digital files with a resolution of300 dpi. They were professionally printed on standardA4 size format (29.7 3 42 cm). Then a photo albumwas assembled containing all images in random order.

The album was given to the 100 raters (50 ortho-dontists, and 50 laypeople with a college educationbut no dental background). Each rater was given infor-mation about the study and asked to evaluate theattractiveness of the images. Along with the album,each rater received a form with 100-mm visual analogscales printed for each image, as in previousstudies.1,7,8,20-23 The scale ranged from “veryunattractive” on the far left to “very attractive” at the

Journal of Orthodontics and Dentofacial Orthopedics

Fig 1. Full-face view of woman number 1, with canine gingival asymmetries in 0.5-mm increments:A, control; B, 0.5 mm; C, 1.0 mm; D, 1.5 mm; E, 2.0 mm; F, 2.5 mm.

Correa, Vieira Bittencourt, and Machado 57

far right. A line was also printed at the midpoint of eachscale as a reference line for an average level ofattractiveness. All raters marked a point along thescale according to their perception of smile esthetics.The scores were then measured in millimeters by thefirst author (B.D.C.) with an electronic digital caliper(Starrett, Suzhou, China).1,8,20-22

To test the reliability of the method, 10 examiners (5laypeople, 5 orthodontists) were randomly selected toevaluate 2 pages of photographs (1 containing a full-face view and the other a close-up view of the smile)with 2 identical images on the same page. Then thescores corresponding to the 2 identical images weretabulated and examined by the intraclass correlationtest with the BioEstat program (version 5.0; Mamirau�aInstitute, Bel�em, Par�a, Brazil). The result (0.72) showedgood reliability of the method.

Descriptive statistics were reported as means andstandard deviations. Differences in the mean esthetic

American Journal of Orthodontics and Dentofacial Orthoped

scores in the 6 levels of asymmetry were analyzed using1-way analysis of variance with the Tukey post-hoc test.To compare the distributions of the mean scores be-tween the full-face and close-up images and alsobetween the orthodontists and laypersons, the Studentt test was used. The level of significance was establishedat 5%.

RESULTS

When comparing assessments of full-face imageswith close-up views, no statistically significant differ-ence was found (P .0.05) (Tables I-IV). After thisresult, the close-up view was used as the reference toaddress the results.

In Table V, according to the orthodontists, in theassessment of the close-up view of the smile for womannumber 1, the highest scores were assigned to the smileswithout asymmetries and with a 0.5-mm asymmetry. For

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Fig 2. Full-face view of man number 1, with canine gingival asymmetries in 0.5-mm increments:A, control; B, 0.5 mm; C, 1.0 mm; D, 1.5 mm; E, 2.0 mm; F, 2.5 mm.


the laypeople, the highest scores were for the smileswithout asymmetries and with asymmetries of 0.5 and1.0 mm. For both groups of raters, the lowest scoreswere assigned for the smiles with asymmetries of 2.0and 2.5 mm (P\0.05).

Table VI shows the results for woman number 2. Theorthodontists assigned the highest scores to the smilewithout asymmetries and the lowest scores to smileswith asymmetries of 2.0 and 2.5 mm. The laypeople as-signed higher scores to the symmetrical smile and smileswith asymmetries of 0.5, 1.0, and 1.5 mm. The lowestscores were for discrepancies of 2.0 and 2.5 mm(P\0.05).

When assessing man number 1, the orthodontists as-signed the highest scores to the smile without asymme-tries and smiles with 0.5 mm of discrepancy. The lowestscore in this group was given to the smile with 2.5 mm ofasymmetry. For laypeople, smiles without asymmetry


and with 0.5, 1.0, and 1.5 mm of asymmetry wereconsidered the most attractive, whereas the asymmetriesof 2.0 and 2.5 mm were considered less attractive (TableVII) (P\0.05).

Table VIII shows the results for man number 2. Theorthodontists assigned higher scores to the symmetricalsmile and the smile with the 0.5-mm discrepancy. Thelowest scores were assigned to the asymmetries of 2.0and 2.5 mm. Laypeople gave higher scores to the smilewithout asymmetries and the smiles with asymmetriesof 0.5 and 1.0 mm. Orthodontists and laypeople as-signed the lowest scores to the discrepancies of 2.0and 2.5 mm (P\0.05).

When comparing the opinions of the orthodontistsand laypeople related to the smiles of the 4 subjects, inmost situations (16 of 24 analyses), a statistically signif-icant difference was found between these groups ofraters (P\0.001). Under these circumstances, in general,


Fig 3. Close-up view of woman number 1, with canine gingival asymmetries in 0.5-mm increments:A, control; B, 0.5 mm; C, 1.0 mm; D, 1.5 mm; E, 2.0 mm; F, 2.5 mm.

Fig 4. Close-up view of man number 1, with canine gingival asymmetries in 0.5-mm increments:A, control; B, 0.5 mm; C, 1.0 mm; D, 1.5 mm; E, 2.0 mm; F, 2.5 mm.


the orthodontists assigned significantly lower scoresthan did the laypeople.

DISCUSSION

Among the factors cited in the literature for opti-mizing smile esthetics is the symmetry between theright and left sides. This study shows that orthodon-tists, in general, did not perceive the asymmetries


between the maxillary canine gingival margins up to0.5 mm, and laypeople did not perceive asymmetriesup to 1.0 to 1.5 mm. This result corroborates the find-ings of Kokich et al,14 who evaluated symmetrical al-terations in the gingival margins of the maxillarycentral incisors in relation to the other teeth in theesthetic zone and concluded that orthodontists canperceive a 1.0-mm discrepancy, whereas laypeopleonly perceived the discrepancy when the alteration


Table II. Means and standard deviations of the attrac-tiveness of the images in full-face and close-up viewsof the smile of Woman 2 for the 2 groups of examiners(P .0.05)

Variable (mm)

Full-face view Close-up view

PMean SD Mean SD0.0 75.6 17.8 77.9 16.4 0.3420.5 68.2 17.5 71.2 15.7 0.0951.0 61.6 18.8 63.4 16.9 0.4791.5 52.8 21.6 55.3 19.3 0.4002.0 35.6 25.0 36.3 21.4 0.8262.5 30.9 23.1 32.8 24.5 0.558

Table III. Means and standard deviations of theattractiveness of the images in full-face and close-upviews of the smile of Man 1 for the 2 groups of exam-iners (P .0.05)

Variable (mm)


PMean SD Mean SD0.0 74.1 17.9 77.9 16.4 0.2020.5 70.0 16.3 73.7 16.3 0.1311.0 58.2 20.5 60.7 18.7 0.3741.5 50.1 22.8 51.7 22.9 0.6052.0 38.7 25.6 42.8 26.2 0.2692.5 34.8 26.6 36.2 25.9 0.702

Table IV. Means and standard deviations of theattractiveness of the images in full-face and close-upviews of the smile of Man 2 for the 2 groups of exam-iners (P .0.05)

Variable (mm)


PMean SD Mean SD0.0 75.8 17.1 77.0 16.2 0.6190.5 69.2 18.4 70.3 15.7 0.6471.0 58.1 17.7 62.6 18.1 0.0791.5 44.6 21.8 48.4 20.8 0.2112.0 35.0 24.2 36.6 23.5 0.6602.5 29.5 25.2 30.1 26.4 0.869

Table I. Means and standard deviations of the attrac-tiveness of the images in full-face and close-up viewsof the smile of Woman 1 for the 2 groups of examiners(P .0.05)

Variable (mm)


PMean SD Mean SD0.0 76.5 17.0 80.2 16.9 0.1200.5 72.1 17.5 71.2 16.7 0.6871.0 60.2 21.3 61.7 19.4 0.6081.5 57.4 22.6 54.8 20.8 0.3972.0 48.3 27.5 42.5 24.8 0.1222.5 40.4 29.9 36.1 26.4 0.282


was 2.0 mm. In another study, Kokich et al15 evaluatedthe perception of alterations in the gingival margin of amaxillary central incisor in relation to its contralateraltooth and found similar results. Orthodontists weremore rigorous in detecting a 0.5-mm discrepancy,and laypeople were less sensitive, only perceiving alter-ations above 2.0 mm.

From a clinical standpoint, a frequently cited estheticparameter is that the closer to themidline, the greater theneed for symmetry; farther away, small asymmetries areacceptable.12 This corroborates the study of Pinhoet al,16 who showed that up to 2.0mmof unilateral toothwear in themaxillary canines was not perceived by ortho-dontists or laypeople when assessing smile esthetics.

An interesting aspect to be discussed is that these find-ings might guide decisions during orthodontic treatment.In a clinical situation, asymmetries between the maxillarycanine gingival margins can occur because of anatomic ormorphologic differences, tooth wear followed by overer-uption, hyperplasia or gingival recession, replacement ofcanines by premolars, and so on. In the latter scenario,because of the absence of a lateral incisor, this tooth canbe replaced by a canine; then a premolar can substitutefor a canine. In those situations, the premolar's gingivalmargin becomes uneven when compared with the canine


on the other side. In these examples, the literature suggestsseveral treatment approaches such as periodontal plasticsurgery,3,13,24 intrusion followed by restoration of theincisal edge,3,18,19,25 or extrusion of the contralateraltooth and incisal grinding.3 In view of our results, beforeestablishing the clinical treatment protocol, the magni-tude of the asymmetry between the canines' gingival mar-ginsmust be assessed because it might not be perceived bylaypeople, and treatment might not be required. In addi-tion, the literature shows that a composite restoration ac-cumulatesmore biofilm than does natural enamel and alsois more prone to discoloration with time.26,27 Followingthe same idea addressed before, correction of slightgingival discrepancies between the maxillary caninesmight reflect an excessive concern by dental specialistsrather than an esthetic need.1,16

Thisfinding is evidentwhencomparing the perceptionsof orthodontists and laypeople. In most situations, ortho-dontists were critical in their evaluations and gave lowerscores to all smiles with asymmetries above 1.0 mm. How-ever, in most situations, laypeople could not detect asym-metries between the canine gingival margins up to 1.5mm. Several studies corroborate this finding.1,8,14-16

Thus, it is evident that any decision during orthodontictreatment must be discussed with the patient.


Table V. Means and standard deviations of the attractiveness of the smile of Woman 1

Variable (mm)

Orthodontists Laypersons

Orthodontists 3 laypersonsMean SD Results* Mean SD Results*0.0 80.73 16.76 A 79.76 17.20 A0.5 73.24 12.56 A 73.08 19.96 A, B1.0 55.41 14.83 B 67.95 21.51 A, B y

1.5 45.77 15.25 C 63.80 21.83 B, C y

2.0 31.09 16.46 D 54.00 26.50 C, D y

2.5 23.32 18.71 D 48.86 26.93 D y

*Variables with the same letter do not differ statistically (P\0.05); ystatistical difference between groups of examiners (P\0.001).

Table VI. Means and standard deviations of the attractiveness of the smile of Woman 2

Variable (mm)


Orthodontists 3 laypersonsMean SD Results* Mean SD Results*0.0 81.61 13.33 A 74.17 18.36 A0.5 69.70 14.12 B 74.56 16.90 A1.0 57.97 15.30 C 68.82 16.83 A y

1.5 46.84 13.29 D 63.70 20.75 A y

2.0 28.31 15.91 E 44.30 23.34 B y

2.5 21.69 17.06 E 43.98 25.92 B y


Table VII. Means and standard deviations of the attractiveness of the smile of Man 1

Variable (mm)


Orthodontists 3 laypersonsMean SD Results* Mean SD Results*0.0 79.50 14.56 A 79.29 18.02 A0.5 72.92 13.21 A 74.52 18.92 A1.0 53.20 11.61 B 68.14 21.46 A y

1.5 43.35 12.19 C 66.12 27.76 A y

2.0 33.46 18.85 D 52.12 29.14 B y

2.5 23.18 16.40 E 49.23 27.19 B y


Table VIII. Means and standard deviations of the attractiveness of the smile of Man 2

Variable (mm)


Orthodontists 3 laypersonsMean SD Results* Mean SD Results*0.0 78.02 14.68 A 75.97 17.71 A0.5 69.55 13.11 A 71.13 18.04 A1.0 56.57 14.30 B 68.53 19.51 A y

1.5 41.40 15.27 C 55.45 23.27 B y

2.0 26.21 15.73 D 41.74 24.85 C y

2.5 18.15 17.76 D 37.02 26.53 C y

*Variables with the same letter do not differ statistically (p\0.05); ystatistical difference between groups of examiners (P\0.001).


When evaluating the full-face view compared withthe close-up view of the smile, no significant differ-ence (P .0.05) was found. These findings agree with


studies by other authors.8,20,21 In this way, it can behypothesized that other components of the face,such as eyes, nose, and hair, do not significantly



influence the assessment of smile esthetics. On theother hand, this result differs from the study ofFlores-Mir et al,28 who found different perceptionswhen laypeople assessed facial photographs in com-parison with close-up views such as intraoral frontalphotographs.

In our study, we used photographs from 4 adults (2men, 2 women) with different smile characteristics.Some studies in the literature that address the perceptionof smile esthetics used only 1 image, usually a whitewoman's smile,15,16,22 and others used more than 1image in the method, which provided a broader viewregarding the influence of 1 variable in the perceptionof smile esthetics.1,8,20-22 Our results were similar whencomparing the smiles of women and men. Furtherstudies are necessary to evaluate different estheticparameters for men because the demand fororthodontic treatment has increased in this groupalong with their esthetic requirements.

Another interesting aspect to evaluate is the reli-ability of the method used in this study. Most studiesdid not test reliability, probably because perception isa subjective evaluation, and there is no need to testthe reproducibility of the measurements.7,8,14-16,20-22

On the other hand, Ioi et al29 used an intraclass testat 2 time intervals to verify whether the examiner couldidentify the same attractiveness in the images atdifferent times. In our study, we corroborated the re-sults of Machado et al,1 and to test reliability, we shuf-fled 2 identical images on the same page at the sametime because, according to the study of Cellerino,30

the level of attractiveness varies from one moment toanother.

Since we used computer-manipulated images from 4patients and the opinions of specific groups of raters, theresults should be carefully analyzed. As stated by Kokichet al,15 since the results and conclusions are based on av-erages, it is difficult to customize this information to apatient because of the subjectivity of smile estheticsevaluation. Therefore, we support their suggestion todiscuss these results with patients who have maxillarycanine gingival asymmetries and then decide whetherto treat it or leave it.

CONCLUSIONS

The outcomes of this study demonstrate thefollowing.

1. In general, the most attractive smiles for orthodon-tists were the ones without asymmetries and the onewith a 0.5-mm asymmetry. For laypersons, the mostattractive smiles were those without asymmetriesand with asymmetries of 0.5, 1.0, and 1.5 mm. For


both group of raters, the lowest scores were as-signed to the smiles with asymmetries of 2.0 and2.5 mm (P\0.05).

2. In most situations, the orthodontists were more crit-ical in their evaluations, giving lower scores than thelaypeople (P\0.001).

3. In general, the results were similar when comparingthe smiles from women and men with respect tomaxillary canine gingival margin asymmetries.

4. No statistically significant difference (P.0.05) wasfound between the full-face and close-up assess-ments of the smiles.

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