Esthetic Smile Perception Among Dental Students at Different Educational Levels

Introduction

An increasing number of Saudi patients are seeking orthodontic treatment with a primary concern of esthetics.¹ Modern dental care aims to enhance beauty, requiring an accurate and thorough analysis of the components that determine the attractiveness of a smile. Esthetics is one of the main reasons for patients seeking dental treatment, and a substantial part of the clinical practice of most dental practices is now influenced by esthetic dentistry.² An attractive smile has long been the focal point of a person’s commitment to enhancing their esthetic image and thereby self-esteem. In addition, the influence of the media on social expectations regarding people’s appearance is likely to have played a role in recent advances in cosmetic dentistry.³

Smile analysis is an essential component of the overall facial analysis conducted by dental specialists. Evaluating the patient’s smile helps the clinician to formulate an accurate treatment plan.⁴ To evaluate a smile, it is appropriate to determine those factors that play an important role in overall dental esthetics and smile aesthetics. Some of these factors include the extent of the incisors’ and gingival exposure at rest and upon smiling, the smile arc, the dental midline relationship to the face midline, tooth proportions, and tooth shade. An esthetically attractive smile depends on the balance between these factors.⁵

The perception of smile esthetics is subjective and is influenced by geographical, racial, cultural, and demographic factors.³ The smile parameters for US and Canadian communities were evaluated by McLeod et al in 2011.⁶ These parameters included buccal corridor, gingival display, occlusal cant, discrepancy of maxillary midline to face, and gingival margin discrepancies. The researchers discovered clinically notable variations in all variables except the buccal corridor. However, the Canadians were more perceptive than the population of the United States.⁴ Significant variations have also been found between German, Russian, and Turkish people in the perception of smile esthetics.⁷

Several studies have been conducted to evaluate the perception of smile esthetics among both dental practitioners and the general public. The vast majority of these studies concluded that these groups vary considerably in their expectations for smile esthetics.^8,9 Among the various dental specialties, orthodontists are more sensitive to dentofacial aesthetics than other dental professionals.^4,10 In comparison, perceptions of aesthetics by dental students have a degree of variability due to the level of dental education they obtain on different aspects of dentistry.¹¹ Dental students play a role as part of the dental workforce, and they should be able to recognize patients’ needs and expectations, make clinical decisions in relation to dental aesthetics, and determine indications for treatment or referral.¹² However, literature on the perception of smile aesthetics among dental students is still scarce.

Despite the many factors that may influence esthetic perception, including feelings, cultural background, and personal experiences,¹³ there seems to be an agreement in the literature that, regardless of these factors, dental students’ perception of smile esthetics improves throughout their study.¹⁴ After the third year of dental school, students begin to focus on more detailed knowledge of dentistry and smile aesthetics (in the clinical module of the curriculum). In comparison to fourth-year students, fifth-year students have seen more patients and received more clinical training.

Most of the studies published on smile esthetics perceptions have focused mainly on assessing the attractiveness of the smile without determining the variables that affect the esthetics of the smile. To the best of our knowledge, no previous studies have compared the perception of smile esthetics among dental students in Medina. Thus, regional research on the appraisal of esthetic smiles is needed, particularly in conservative societies such as Al Madinah Al Munawwarah, where veil use predominates among women of all age groups. The aim of this study was to evaluate the perception of six smile esthetic components among dental students and whether such a perception was influenced by gender or clinical training.

Materials and Methods

Study Design, Setting, and Sampling

This was an exploratory analytical cross-sectional study conducted at college of Dentistry, Taibah University, AlMadinah AlMunawwarah, Saudi Arabia (SA) over the period between September 2017 and May 2018. The study has invited all the students (n=182) who attended 4th and 5th year levels. The students at these levels are expose to the knowledge and the clinical experience of smile esthetics training of orthodontics. Fourth year preclinical orthodontics is mainly conducted in the dental laboratory. Fifth year clinical orthodontics involving patient examination, development of a problem list. Students must be aware of the basic concepts of smile esthetics because addressing it involves a multidisciplinary approach rather than orthodontics alone.

Data Collection Tool and Assessment of Smile Esthetics

A self-administered paper and pencil questionnaire was distributed to all participating fourth- and fifth-year dental students in the classroom prior to their scheduled lectures. The questionnaires were anonymous, and participation was voluntary. The questionnaire contained a cover page that explained the study objectives; information about the ethical committee approving the study, for any inquiries and complaints; the email address of the researcher; and the time needed to fill out the form. There were two sections of the questionnaire: section one asks questions about socio-demographic characteristics (eg, gender and level of education). In section two, participants were asked to assess esthetic smiles using a 10-point visual analogue scale (VAS), of which the right end of the scale is labeled “attractive smile” and represented by the number 10, and the left end of the scale is labeled “unattractive smile” and represented by the number 0. A coloured smile photograph was obtained of the female smile (The images were obtained from researcher’s sister, who gave informed consent) using a digital camera (Nikon Coolpix 5000; Melville, New York, USA) in the frontal pose. A female individual was chosen who had a smile with characteristics close to standard norms as reported in the literature.^15,16 Several photographs were taken so that natural smiles could be obtained. The pictures were taken under the same environmental and lighting conditions and standardized using Adobe Photoshop (Adobe Systems Inc., San Jose, CA, USA). A total of 26 digital images (Figures 1 and 2) were presented to the participants, each showing a frontal view of female smiles with similar skin tones. These images were selected to exhibit six different aspects or variables of smile esthetics. Each variable has one ideal image with other altered images of the same variable. All images were cropped to show the smile alone and remove the chin, nose, and cheeks to eliminate any conflicting variables that could influence the perception of a smile.^17,18 These images were digitally edited using Adobe Photoshop software (Adobe Systems Inc., San Jose, CA, USA): the images were purposely adjusted to mimic a smile’s esthetic variations. Then, the images were condensed or enlarged after the alterations were made to achieve an image size representing actual tooth size. The images were presented to the participants via Microsoft PowerPoint (Microsoft Corp., Microsoft Office 2016, NY, USA). The sequence of the images was randomized for each smile variable. The participants were given one minute to evaluate each image as reported previously.¹⁹ The images were divided into six sets (Figures 1 [Image 1–3] and 2 [Image 4–6]), each set based on a variable describing an aspect of smile esthetics. These variables include:

1. Smile Arc. The image was altered by flattening and accentuating the curvature of the anterior teeth relative to the curvature of the lower lip (Figure 1, Image 1).
2. Buccal corridor. The image was altered by widening and narrowing the space between the posterior teeth buccal surfaces and the lip commissures (Figure 1, Image 2).
3. Gingival display upon smiling. The anterior gingival display was measured from the lower border of the upper lip till the gingival margin of the anterior teeth. The gingival show (gingiva-to-lip distance) was increased by 1 mm increments to create a “gummy” smile. Modifications were based on the relationship of the upper lip with the gingival margin of the maxillary incisors. The image was altered by increasing the amount of gingival show upon smiling, from 1 mm to 4 mm increase (Figure 1, Image 3).

   Figure 1 Aspect of smile esthetics for smile arc, buccal corridor, and gingival display.

4. Midline diastema. The image was altered by creating a midline diastema between the maxillary central incisors by 0.5 mm increments up to 2 mm (Figure 2, Image 1).
5. Crown length. The image was altered by decreasing the crown length of the maxillary left central incisor by adjusting the gingival marginal level by 0.5 increments up to 2 mm. The reference point used for these measurements was the most superior point on the labial gingival margin of the adjacent right central incisor. An anterior tooth was selected so that we can reproduce the crown length alterations more easily (Figure 2, Image 2).
6. Crown width. Maxillary tooth width proportions provide an example of the golden proportion. The width of the lateral incisor should be around 62% of the width of the central incisor.¹⁰ The size of maxillary right lateral incisor was altered digitally to obtain an incremental decrease in lateral-to-central width proportion in contrast to the ideal smile that followed the golden-proportion (62%). The most common variation in incisor crown width is usually associated with the size of the maxillary lateral incisors; hence, the alterations of crown width were made to the maxillary lateral incisor. The image was altered by decreasing the mesiodistal width of the maxillary right lateral incisor by an increment of 1 mm up to 4 mm crown width reduction (Figure 2, Image 3).

Figure 2 Aspect of smile esthetics for midline diastema, length of the left crown maxillary central incisors and width of the lateral maxillary incisor crown.

Ethical Considerations

This study was approved by the Dentistry Research Ethics Committee at Taibah University Dental College and Hospital (TUCDREC/20180127/Nazar). The study was conducted in accordance with the principles of the World Medical Association, Declaration of Helsinki. Participation in the study was voluntary, and the confidentiality of the collected data were assured—ie, the questionnaire was anonymous and coded. The completion and return of the questionnaire were a proxy for consent to participate.

Statistical Analysis

The data were analyzed using the Statistical Package for the Social Sciences (SPSS) software, version 16.0 (SPSS, Inc., Chicago, IL, USA). Descriptive statistics that included median and interquartile range (IQR) for continuous variables and frequencies with percentages (F [%]) for categorical data were run to report sample characteristics. Comparisons between dental students at fourth level, fifth level, male and female dental students collectively and at each level (fourth and fifth year) were undertaken. The comparisons were performed using the non-parametric analysis Mann–Whitney U-test as all the continuous data did not adhere to normality distribution (Kolmogorov–Smirnov ≤0.05). Median (IQR) was reported for comparisons and when there were ties in medians, ie, medians were identical, the mean rank checked to aid interpretation of identical medians. The significance level was set at 0.05 (P≤ 0.05).

Results

Of all the invited students (182), the number of participating students as 145) (response rate 80%), of whom 77 (53.1%) were females and 68 (46.9%) were males. Fifty-four percent (35 female and 43 male) were in the fourth year and forty-six percent (42 female and 25 male) were in the fifth year.

Table 1 displays smile esthetics evaluation between male and female dental students at fourth and fifth year (n=145 [Female= 77, Male =68]). In evaluating ideal smile esthetic images (A), both male and female were scored comparably higher toward attractive esthetic for the smile arc, buccal corridor, gingival display, midline diastema, crown length and width and the difference between the two groups was non-significant (p=0.919, 0.205, 0.347, 0.902, 0.145 and 0.062, respectively). In addition, both groups were comparable on the altered images evaluation of smile arc, buccal corridor (p=0.778 and 338)). On the other hand, there was a statistical significant difference between male and female dental students median scores (p<0.05) at the altered smile esthetics evaluation in all smile variables (B, D and E). Male median scores were statistically significantly (p<0.05) higher than females towards unattractive aesthetics in gingival display (E), midline diastema (B, D), crown length (B, E) and crown width (D) meanwhile females scores were higher at gingival display (B).

Table 1. Comparison of Median Esthetic Scores of Different Smile Esthetics Variables as Evaluated by Male and Female Dental Students Collectively at Fourth and Fifth Year (n=145 [Female= 77, Male =68])

As for gender differences in academic level year four (n=78 [Female=35, Male=43]), Table 2 shows that the gender differences in scoring ideal esthetic smile for all variables were non-significant (p>0.05), except crown length where males scored statistically significantly higher towered ideal smile esthetics (p=0.019). As for the evaluation of altered smile esthetics fourth year male dental students scored statistically significantly (p<0.05) higher than females toward the unattractive esthetic smile for gingival display (C, D and E), midline diastema (D) and crown length (B, C).

Table 2. Comparison of Median Esthetic Scores of Different Smile Variables as Evaluated by Male and Female Dental Students at Fourth Year (n=78 [Female=35, Male=43])

With regard to gender differences in academic level year five (n=67 [Female=42, Male=25]), Table 3 shows that ideal smile esthetics evaluation for all smile variables images (A), the gender differences were non-significant (p>0.05). However, female dental students scored higher towered unattractive esthetic smile in altered smile images in the following smile variables: gingival display (B), midline diastema (E) and crown length (C) and the difference was statistically significant (p<0.05). On the other hand, male dental students scored higher towered unattractive esthetic smile in altered smile images compared to female counterparts in the following smile variables: midline diastema (B), crown length (E) and crown width (D) and the difference were statistically significant (P=0.006, 0.005 and 0.014, respectively).

Table 3. Comparison of Median Esthetic Scores of Different Smile Variables as Evaluated by Male and Female Dental Students at Fifth Year (n=67 [Female=42, Male=25])

Table 4 shows the differences in the academic level in evaluating smile esthetics (n=145 [fourth year=78, fifth year=67]). Students at level five scored statistically significantly (p<0.001) higher towered attractive esthetic smile in ideal smile arc image (A), while students at level four scored statistically significantly (p=0.016 and 0.006, respectively) higher towered attractive esthetic smile in ideal gingival display and crown length image (A). At altered smile esthetics evaluation, fifth year dental students scored statistically significantly (p=0.030, 0.026 and 0.028 respectively) higher towered unattractive esthetic smile in smile arc (B, C) and buccal corridor (C). On the other hand, fourth year dental students scored statistically significantly (p=0.022, 0.048, 0.027 respectively) higher towered unattractive esthetic smile in gingival display (C), midline diastema (D) and crown width (D).

Table 4. Comparison of Median Esthetic Scores of Different Smile Variables as Evaluated Collectively by Fourth- and Fifth-Year Dental Students (n=145 [Fourth Year=78, Fifth Year=67])

Discussion

Dental schools are responsible for ensuring the graduation of experienced clinicians who are independently qualified to practice dentistry. In current dental practice, esthetic dentistry is emerging rapidly.²⁰ Dental students are usually required to treat patients during their undergraduate training. Therefore, in order to reach an accurate diagnosis and to plan the required treatment, it is crucial to teach dental students the principles of dentofacial esthetics.^14,21,22

In the present study, six principal smile variables affecting the beauty of the smile—that is, smile arc, buccal corridor, gingival display, midline diastema, crown length, and crown width—were evaluated by dental students.²³ Six sets of images were digitally manipulated, inducing minor modifications to investigate the effects of dental education, clinical training, and gender differences on the esthetic perception of smiles. A VAS was used to judge smile attractiveness. Various studies have adopted the use of the VAS as a study tool.^1,4,12 To ensure consistency in presentation, PowerPoint presentations were performed in large classrooms that can accommodate up to 200 students.

This study involved investigating the influence of gender and education level on the perception of smile esthetics. This study found that there was no statistically significant difference (p>0.05) in esthetic perceptions toward attractive smiles and altered smiles images of smile arc, buccal corridor (p>0.05) between males and females. These results are comparable to those described in Bukhary’s study.^14,17,24 In the light of the literature, it is suggested that the gender effect in dentofacial esthetic perception is highly dependent on culture. Despite this, females were likely to score numerically higher and toward the attractive esthetic smile than males for gingival display and midline diastema.¹⁶ This is in agreement with the findings of Abu Alhaija et al,¹⁶ who reported that gender affects the smile attractiveness rating, and females were more sensitive to the presence of a gingival display and midline diastema than males. In contrary to the results of Moore et al²⁵ and Ioi et al,²⁶ who indicated that males and females rated smile attractiveness comparably.^25,26

The maxillary left central incisor’s crown length was altered in our study. Crown length alterations were made by adjusting the gingival marginal level by 0.5 increments up to 2 mm. Changing the proportions of the tooth reduces the perception of an esthetic smile.^7,12,14,27 Moreover, any decrease in the tooth length or width is considered to decrease the smile’s attractiveness when rated by either dentists or laypersons.^24,28 Asymmetric gingival marginal level was perceived as unattractive by female dental students. They scored statistically significantly toward an unattractive esthetic smile in respect of crown length (p>0.05). This finding is similar to that reported by Alhammadi et al²² However, ideal smile esthetics evaluation for crown length images showed that gender differences were non-significant (p>0.05). In agreement with previous studies, no significant gender difference was found with respect to the gingival marginal level and crown length.^12,14,17,24

In addition, the maxillary right lateral incisor’s clinical crown width was modified. In our study, ideal smile esthetics evaluation for crown width images showed that gender differences were non-significant (p>0.05). However, the perception of correct lateral incisor crown width is higher among female dental students.

As for the academic level differences in evaluating smile esthetics, students at level five scored statistically significantly (p<0.05) higher towered attractive esthetic smile in ideal smile arc image and at altered smile esthetics evaluation in gingival display, midline diastema, and crown width.^12,22 However, the findings support previous research that shows a link between dental knowledge (expressed as an academic level in this study) and esthetic perception of dentofacial features. Armalaite et al¹⁸ assessed how the characteristics of smiles are perceived by dental students. They reported that among dental students, fifth year dental students were more critical when evaluating smile esthetics. Alhammadi et al²² reported that clinical training has a significant positive effect on smile esthetic evaluation. This is, however, contrary to the findings of a study by Sakellaropoulos et al²⁹ which indicated that education level was not an important factor.

Our study has a few limitations. The use of a female smile as the only model image is one of the study’s limitations, as it has been shown that the gender of the model smile image influences smile attractiveness rating.¹⁶ Hence, the results may not be generalizable.^4,16 Another limitation was the simultaneous presentation of images to all students in classrooms. The location of the students in the classroom may have influenced their responses and students may not have had the same view of the screen. This could have been combined with the students’ vision acuity and normal color discrimination ability. The presence of disease/illnesses/disorders was not an exclusion criterion for participation in the study.²⁹ Finally, our study did not take into account the socio-economic status of dental students, which may have affected the outcomes. As for recommendations, studying how specific curricular material affects students’ dentofacial esthetic experience would appear to be a promising path for future studies. Dental students should be encouraged to discuss variations in the understanding of smile aesthetics while addressing patients’ treatment plans. Moreover, dentofacial esthetic evaluation should include both male and female smile images to explore the evaluators’ differences in terms of same gender smile image (Male-Male; Female to female, Male-Female and Female-Male) assessment. As for the clinical relevance, this study highlighted that more efforts should be done on both the dedicated and training of students of assessing esthetic smile. Specific focus should be paid to senior students who will be soon independent dentist serving the community. This is crucially important in order to be able to fulfill the patient’s esthetic needs and expectations.

Conclusion

The findings of this study showed that dental students at the fifth year level (clinical level) generally had higher perception of aesthetic components of the smile than those at the fourth year level. Regardless of the level of study, female dental students had higher perceptions of esthetic components of the smile than males.