Evaluating the Impacts of Some Etiologically Relevant

Volume 41, Number 3, 2021

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Submitted October 7, 2020; accepted November 30, 2020. ©2021 by Quintessence Publishing Co Inc.

The literature offers limited and even conflicting information on the etiology of gummy smile. Therefore, this study aimed to evaluate smile line, hypermobile upper lip (HUL), altered passive eruption (APE), and short upper lip (SUL) distribution in a group of patients seeking dental treatment and to examine their effects on gummy smile. A total of 501 individuals (265 men, 236 women) were included in the study. The patients were grouped by gingival display, and presence of HUL, APE, and SUL were evaluated. Multivariate Logistic Regression analyses were performed to investigate the impact of possible risk factors on gummy smile. Of the individuals, 173 (34.5%) had a low smile line, 127 (25.3%) had an average smile line, 146 (29.1%) had a high smile line, and 55 (10.9%) were gummy smile patients. Individuals with gummy smile were younger than the individuals with low smile line (P < .001). As for the possible risk factors for gummy smile, age (odds ratio [OR]: 0.936; 95% CI: 0.901 to 0.972; P = .001), HUL (OR: 18.85; 95% CI: 7.82 to 45.44; P < .001), and APE (OR: 8.819; 95% CI: 3.894 to 19.973; P < .001) were found to be significant together. Gender and SUL/upper lip length were not found to have any impact on gummy smile. HUL is the primary factor that increases the probability of having gummy smile, followed by APE as the secondary factor. It seems reasonable to focus on correction of the HUL for treatment in most gummy smile patients. Int J Periodontics Restorative Dent 2021;41:e73–e80. doi: 10.11607/prd.5475

Evaluating the Impacts of Some Etiologically Relevant Factors on Excessive Gingival Display

1Department of Periodontology, Faculty of Dentistry, Baskent University, Ankara, Turkey. 2Department of Biostatistics, Faculty of Medicine, Ankara University, Ankara, Turkey. Correspondence to: Dr Mehtap Bilgin Çetin, Baskent University, Faculty of Dentistry, Department of Periodontology, Bahçelievler, Ankara 06790, Turkey. Fax: +90 312 246 66 15. Email: [email protected]

Smile is one of the most important facial expressions and known as the parameter of nonverbal communi-cation that expresses joy.1 Smile af-fects the professional life and confi-dence of individuals, as well as how they socialize with others.2 Thus, acquiring an esthetic smile is a sig-nificant treatment goal for both phy-sicians and patients.3

An attractive smile is composed of three main parts (teeth, lip frame-work, and gingival scaffold) and is closely related to the amount of ap-parent gingiva.4–6 Smile line (SL) is an important tool utilized to evalu-ate whether a smile is esthetic. SL has been classified by several re-searchers7,8; Liébart et al9 also took interdental papilla into account and evaluated it in four categories: low, average, high, and very high SL. Very high SL in which gingiva is ap-parent at maximum is also called “gummy smile” (GS). Such high vis-ibility of gingiva is not homogenous in every patient, and therefore, GS was classified by Wu et al in four groups by its localization.10

Etiology of GS is multifacto-rial. Although three conditions—hy-permobile upper lip (HUL), altered passive eruption (APE), and vertical maxillary excess10—mainly cause GS, short upper lip (SUL), genetics, dental plaque, and medication11 can also lead to excessive gingival display (EGD). Among these, HUL,

Mehtap Bilgin Çetin, DDS, PhD1

Yasemin Sezgin, DDS, PhD1

Seray Akıncı, DDS1

Batuhan Bakırarar, DDS, MSc2

© 2021 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER. © 2021 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

mailto:[email protected]

The International Journal of Periodontics & Restorative Dentistry

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SUL, and APE are thought to be soft tissue etiologic factors result-ing in EGD.11 There are few stud-ies on the etiology of GS, and the literature offers limited and even conflicting information on the mat-ter. For example, prevalence of SUL has not been reported before,12 and there is contradictory information on the place of SUL within the etiol-ogy of GS.11,13–15 Prevalence of HUL in GS has only been reported in one study.12 APE, another etiological fac-tor for GS, has only been evaluated in some specific populations.12,16 Moreover, no study has been con-ducted to evaluate any factor that might be a risk for GS. It is therefore important to evaluate these factors together due to the multifactorial nature of GS. Based on the gap of literature in this field, the present study primarily aimed to evaluate SL distribution and frequency of HUL, SUL, and APE in a group of patients seeking dental treatment. The sec-ondary purpose was to examine the effects of HUL, SUL, and APE on GS.

Materials and Methods

Patients who presented to Baskent University Faculty of Dentistry for a variety of reasons between No-vember 2019 and February 2020 were included in the study. The study was approved by Baskent Uni-versity Institutional Review Board (Project no: D-KA 20/08) and sup-ported by Baskent University Re-search Fund. This cross-sectional study is registered at ClinicalsTrials.gov (NCT04553952) and was con-ducted in compliance with the prin-

ciples of the Declaration of Helsinki (2008). All patients gave their writ-ten consent before participating in the study. The following inclusion criteria were applied: presence of teeth in the maxilla, and aged be-tween 18 to 65 years. Patients who had received and/or were receiving orthodontic treatment and patients who had received prior GS treat-ment were excluded from the study.

All screening procedures were performed by one trained and cali-brated examiner (S.A.). The kappa values were 0.961 (95% CI: 0.888 to 0.987), 0.962 (95% CI: 0.891 to 0.987), 0.954 (95% CI: 0.872 to 0.984), and 0.984 (95% CI: 0.954 to 0.995) for gingival display, HUL, APE, and SUL measurements, respectively (P < .05).

Identifying the SL

Age, gender, marital status, medi-cal history, and medication status of the patients were recorded. All in-dividuals were instructed to sit on a dental chair, and the measurements were taken using a millimetric ruler. SL was determined by measuring the visibility of the gingiva at maxi-mum smile, and the patients were grouped according to Liébart’s classification as follows9: (1) Class 1: excessive gingival display (≥ 3 mm; GS); (2) Class 2: high SL, 0 to 2 mm of gingival display; (3) Class 3: av-erage SL, dental papilla is visible; (4) Class 4: low smile line, and gingi-val margin and dental papilla are not visible at all.

GS Classification and Evaluation of Etiological Factors

Patients who had EGD were cat-egorized into one of the GS subcat-egories according to the following criteria10: (1) Type I, where maxillary gingiva is seen like a band; (2) Type II, where posterior parts of maxillary gingiva are seen; (3) Type III, where maxillary gingiva is seen unilaterally; (4) Type IV, where the front part of maxillary gingiva is seen.

To determine whether an in-dividual had HUL, upper lip mobil-ity from rest to maximum smile was measured over the maxillary right central incisor.7,12,17 First, the dis-tance between the subnasal area and the lower edge of the upper lip was measured at rest. Then the same measurement was repeated at the maximum smile. Patients with a difference of more than 8 mm between the two measurements were categorized as having HUL (Fig 1). Where the width/height ra-tio of maxillary incisors was > 0.85 and teeth appeared in a short and square form, presence of APE was considered (Fig 2).12,18,19 The midline distance between the subnasal area and lower edge of upper lip was measured; values < 20 mm in men and < 18 mm in women were de-fined as SUL (Fig 3).20 Presentation of types of GS in different patients are shown in Fig 4.



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a b

Fig 1 Measurement of a hypermobile upper lip. The distance between the subnasal area and the lower edge of the upper lip was measured (a) at rest and (b) at maximum smile. Patients with a difference of more than 8 mm between the two measurements were categorized as having hypermobile upper lip.

Fig 2 Altered passive eruption was considered if the width (w)/height (h) ratio of maxillary incisors was > 0.85.

Fig 3 Measurement of the upper lip length. This patient had a 17-mm lip length, classified as a short upper lip.

wh

Fig 4 Clinical images of different patients having gummy smile: (a and b) hypermobile upper lip and (c) short upper lip and altered passive eruption.

a b c

Statistical Analysis

SPSS version 11.5 (IBM) was used for the data analysis. Mean ± SDs and median (minimum to maximum) were utilized for quantitative vari-ables, and number of patients (per-centage) was utilized for qualitative

variables as descriptors. For quan-titative variables, Mann-Whitney U test was performed to see whether there was a statistically significant difference between categories of the qualitative variable with two cat-egories. To examine the relationship between two qualitative variables,

chi-square test was used. Univariate and multivariate logistic regression analyses were utilized to determine the risk factors deemed to have an effect on the dependent quantita-tive variable. Statistical significance level was accepted to be .05.



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differences were found between the groups (P < .001). Considering the paired groups with Bonferroni- corrected Mann-Whitney U test, dif-ferences between GS and high SL, GS and average SL, GS and low SL, and high SL and low SL were found to be statistically and significantly dif-ferent (P = .046, P < .001, P < .001, and P < .001, respectively).

Distribution of SLs by gender is presented in Fig 6, and Fig 7 shows how presences of APE, HUL, and SUL were distributed among the GS patients. Of the GS patients, 3.6% were found to have HUL, APE, and SUL together, whereas none of the etiologic factors addressed in this study were observed in 7.3% of the patients.

In Table 1, individuals with gum-my smile (GS+) and without gummy smile (GS–) are compared by the variables of age and gender and pa-rameters of HUL, APE, SUL, and up-per lip length (ULL). The mean age of GS+ patients was 28.44 ± 7.87 years, the mean age of GS– patients was 38.42 ± 14.92 years, and the dif-ference between the groups was significant (P < .001). Percentage of women in the GS+ group (65.5%) was found to be higher than the per-centage of women in the GS– group (44.8%; P < .001).

Tables 2 and 3 present results of the univariate and multivariate logistic regression analyses, respec-tively. In the model, the variables age (P = .001), HUL (P < .001), and APE (P < .001) were found to be significant together. An increase of one unit in the quantitative vari-able of age reduces the risk of hav-ing GS by ×0.936 (95% CI: 0.901 to

Type I Type II

Stud

y p

opul

atio

n (%

)St

udy

pop

ulat

ion

(%)

Type III

40

35

30

25

20

15

10

5

0Type IV Class II Class III Class IV

34.5%

25.3%

29.1%

6.7%

2.4% 1.2% 0.6%

Fig 5 Distribution of smile lines in the study population. Types I, II, III, and IV pertain to different classifications of Class I (gummy smile). Class II = high smile line; Class III = average smile line; Class IV = low smile line.

7570656055

5045

4035302520

15105

0Class IIClass I

Male Female

Class III Class IV

34.5%

65.5%

49.3%50.7%

64.7%

35.3%

48.8%51.2%

Fig 6 Distribution by gender of smile lines in the study population. Class I = gummy smile; Class II = high smile line; Class III = average smile line; Class IV = low smile line.

Results

A total of 501 patients (265 men, 236 women) were included in the study. Of these patients, 173 (34.5%) had low SL, 127 (25.3%) had average SL, 146 (29.1%) had high SL, and 55

(10.9%) were GS patients (Fig 5). For the age variable, mean values of low, average, high, and GS groups by SL were calculated to be 43.01 ± 16.69 years, 37.46 ± 13.48 years, 33.82 ± 12.15 years, and 28.44 ± 7.87 years, respectively; statistically significant



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Stud

y p

opul

atio

n (%

)

None

HUL

APE SUL

HUL+APE

HUL+SU

LAPE

+SUL

HUL+APE

+SUL

40.0%

3.6%

45.0

40.0

35.0

30.0

25.0

20.0

15.0

10.05.0

0.0

7.3%

41.8%

1.8% 1.8%1.8% 1.8%

Fig 7 Distribution of hypermobile upper lip (HUL), altered passive eruption (APE), and short upper lip (SUL) in the gummy smile population.

Table 1 Characteristics of the Study Population

Parameter

Study population (n = 501)

PGS– (n = 446) GS+ (n = 55)

Gender, n (%)

Male 246 (55.2) 19 (34.5).004a

Female 200 (44.8) 36 (65.5)

Presence of HUL, n (%)

Yes 103 (23.1) 48 (87.3)< .001a

No 343 (76.9) 7 (12.7)

Presence of SUL, n (%)

Yes 38 (8.5) 5 (9.1).801

No 408 (91.5) 50 (90.9)

Presence of APE, n (%)

Yes 23 (5.2) 26 (47.3)< .001a

No 423 (94.8) 29 (52.7)

Age, y

Mean ± SD 38.42 ± 14.92 28.44 ± 7.87< .001b

Median 36.50 26.00

Minimum, maximum 10.00, 90.00 14.00, 47.00

ULL, mm

Mean ± SD 22.59 ± 3.20 22.44 ± 3.15.708b

Median 23.00 23.00

Minimum, maximum 15.00, 33.00 16.00, 30.00

GS = gummy smile; GS+ = with GS; GS– = without GS; HUL = hypermobile upper lip; SUL = short upper lip; APE = altered passive eruption; ULL = upper lip length.aChi-square test.bMann-Whitney U test.



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0.972). Presence of the HUL variable increases the risk of having GS by ×18.853 (95% CI: 7.822 to 45.442). Similarly, presence of the APE vari-able increases the risk of having GS by ×8.819 (95% CI: 3.894 to 19.973).

Discussion

The purpose of the present study was: (1) to determine the distribution of SL and frequency of HUL, SUL, APE, and (2) to evaluate the impact of the HUL, SUL, and APE on GS. The study results show that a major-ity (34.5%) of the sample population consisted of individuals with low SL, whereas 10.9% of the study popula-tion had GS; the parameter that had

the highest relationship with GS was HUL (odds ratio [OR]: 18.85; 95% CI: 7.82 to 45.44; P < .001).

Patients may smile differently depending on what they feel at a given moment, and it can lead to various natural smiles for the same patient. This makes forced smile more advantageous than natural smile in terms of repeatability. Simi-lar to another study,21 the present study participants were evaluated at their forced smiles, and the evalu-ation of SL was based on Liébart’s classification. There are different prevalence values for the distribu-tion of SL in various populations in the literature.7–9,22,23 Findings from the present study coincide with the results achieved by Jensen et al8 but

differ from other results in the litera-ture.7,9,22,23 The difference might be due to the fact that studies in the literature were conducted on very different populations.

It is emphasized in the litera-ture that low SL creates a masculine smile characteristic, while high SL is attributed to a rather feminine smile characteristic.24,25 In line with another study,26 the GS+ group in the present study population is mainly composed of women; how-ever, gender was not found to have any impact on GS. Because such a risk assessment has not been done before, it is not possible to directly compare this result with others.

In some previous studies, the condition where the upper lip

Table 2 Univariate Logistic Regression Analysis for Association of Gummy Smile

Parameter β SE P OR

95% CI

Lower limit Upper limit

Age –0.065 0.014 < .001 0.937 0.911 0.964

Gender (Male) 0.846 0.299 .005 2.331 1.297 4.189

Presence of HUL 3.128 0.420 < .001 22.835 10.027 52.002

Presence of APE 2.730 0.345 < .001 15.326 7.791 30.150

Presence of SUL 0.071 0.499 .887 1.074 0.404 2.854

SE = standard error; OR = odds ratio; CI = confidence interval; HUL = hypermobile upper lip; APE = altered passive eruption; SUL = short upper lip.

Table 3 Multivariate Logistic Regression Analysis for Association of Gummy Smile

Variables β SE P OR

95% CI

Lower limit Upper limit

Age –0.066 0.019 .001 0.936 0.901 0.972

Presence of HUL 2.937 0.449 < .001 18.853 7.822 45.442

Presence of APE 2.177 0.417 < .001 8.819 3.894 19.973

Constant –2.100 0.666 .002 0.122 – –

SE = standard error; OR = odds ratio; CI = confidence interval; HUL = hypermobile upper lip; APE = altered passive eruption.



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moves higher than 8 mm at maxi-mum smile has been considered HUL.12,17 In the present study, this threshold value was used for the diagnosis of HUL, and frequency of HUL in individuals with GS was found to be 87.3%. There is one study that reports prevalence of HUL in GS patients in the literature.12 Un-like the study performed by Andijani and Tatakis,12 prevalence of HUL in the present study was also evalu-ated in the group of GS– individuals and found to be 23.1%. Prevalence of HUL in the GS+ group was found to be significantly higher than in the GS– group (P < .001), indicating that HUL has a significant place within the etiology of GS.

First defined by Coslet et al,27 APE is a condition that causes EGD, and teeth are seen shorter and in the square form in its presence. In the present study, APE was diagnosed based on the width/height ratio of maxillary anterior teeth, like in a previous study.12 Prevalence of APE ranged from 12% to 55% in stud-ies conducted on specific popula-tions.14,16,28 In the present study, APE was seen in 47.3% of GS+ patients and 9% of the total population. Unlike the previous study,12 the fre-quency of APE was also evaluated in individuals with GS–, and frequency of APE was found to be significantly higher in the GS+ group than in the GS– group (P < .001). This is an ex-pected result for APE, which has an important role in the etiology of GS.

The study findings did not ob-serve any significant difference be-tween the groups both by ULL and SUL. In the relevant literature, con-tradictory findings are observed in

the effect of ULL on SL. Although SUL has been reported to be a pa-rameter that affects EGD,11,29 some researchers reported that ULL is not to be associated with GS.7,13–15,30 Schendel et al15 compared ULL of individuals with and without GS and reported that both groups had the same lengths. In fact, Singer14 re-ported ULL of women with GS to be longer than those without GS. Similarly, Roe et al13 reported that individuals with short and normal ULLs had no remarkable difference by gingival display. In the present study, ULL and GS were not found to be correlated.

The present study performed a risk assessment for GS, and in the multivariate logistic regression analysis, the riskiest parameter was found to be HUL, followed by APE. Because there is no study that has conducted a risk assessment for GS in the literature, it is not possible to compare these results. Alternatively, Andijani and Tatakis found quite a high prevalence of HUL in GS patients, coinciding with the present results.12

It is notable that etiologic fac-tors evaluated in about half of the GS+ group are present in several combinations. This result supports that GS has a multifactorial etiology and therefore its treatment requires a clinician’s mastery. APE may be re-solved with gingivectomy/apical flap positioning (with and without bone resection). In case of SUL and HUL, lip repositioning surgery, which is a surgical procedure, is a treatment option. Another treatment option for the HUL is injection of botulinum toxin type A, which is a nonsurgical

application. Other recommended treatment modalities are orthodon-tic intrusion and orthognathic sur-gery with or without periodontal and restorative therapy. Depending on the combination of existing etio-logic factors, one or more of these treatment options can be used for the treatment of GS.11

To the best of the present au-thors’ knowledge, this study is the first to examine the frequency of SUL in patients seeking dental treatment and to perform risk assessment for GS, thus achieving new findings in this field. However, some limita-tions should be considered when interpreting the results, the first of which is the lack of the evaluation of all etiologic factors, such as verti-cal maxillary excess or dentoalveolar extrusion. Another limitation may be that the population consisted of pa-tients who applied to the dental fac-ulty for several reasons. Therefore, extensive studies that evaluate all etiologic factors of GS are required to understand the role of these fac-tors together on GS.

Conclusions

The results show that 10.9% of the study population had GS. In addition, HUL was found to be the primary factor that increased the probability of having GS, which was followed by APE, and the majority of the study population had a low SL. There was no relationship between SUL/ULL and GS. Further studies are needed to clarify and confirm these findings.



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Acknowledgments

The authors declare no conflicts of interest related to this study.

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Evaluating the Impacts of Some Etiologically Relevant