Evaluation of Smile Line in Natural and Forced Smile Position : An Institution-based Study

Introduction: Smile line is a major factor considered in esthetic treatment planning. Objective: To assess the position of the smile line both in natural and forced position in relation to age and gender in Nepali population sample. Materials & Method: A cross sectional study was done in 220 adults. DSLR camera was used to take photograph of the participants. Two different photographs were taken of each participant in natural and forced smile position in standardized format. The smile lines were determined and classified according to Liebart et al. Data analysis was done by SPSS 20.0 software. Chi square test was performed to analyze statistical significance between the gender and age groups Result: Maximum individuals had low type of natural smile (59.1%) and average type of forced smile (40.0%). Very few individuals had very high type of natural smile (1.4%) and very high type of forced smile (15.9%). Among all, 41% had visibility of the periodontium during normal smile while on forced smile 79.1% had visibility of the periodontium. Conclusion: Females have significantly more periodontal visibility when compared to males during forced smile in Nepali population sample. This concept of smile line should be utilized for treatment planning to achieve desirable facial esthetics in many fields of dentistry including Orthodontics, Prosthodontics, Periodontics, Restorative Dentistry.


INTRODUCTION
Smile is an involuntary action denoting happiness, pleasure, sociability, appreciation or amusement.It comes from inner satisfaction and is a means of nonverbal communication.It evolved from a need to communicate and is contagious.Smile plays an important role in social acceptance, interaction, and development of personality.

MATERIALS AND METHOD
A

RESULT
The

Classification of Smile Line
Natural smile (Figure 1a) and forced smile (Figure 1b) were examined according to Liebart classification. 8Class 1 (Very high smile line): More than 2 mm of marginal gingiva visible or more than 2 mm apical to the CEJ visible for the reduced but healthy periodontium.This could be the 'gummy smile' (Figure 2a).
• Class 2 (High smile line): Between 0-2 mm of marginal gingiva visible or between 0-2 mm apical to the CEJ visible for the reduced but healthy periodontium (Figure 2b).
• Class 4 (Low smile line): Gingival embrasures and CEJ are not visible (Figure 2d).Arabian subjects revealed majority of the participants had low type of normal smile line (41%). 10The findings of the present study were slightly different from study done in Europe by Liebart et al, 8 where most common type was average type for both normal (44.79%) and forced smile (45.49%).
In our study least percentage of participants had very high type of natural smile (1.4%) and very high type of forced smile (15.9%).This finding differed from previous study done by Liebert et al 8 where least common was very high type of natural smile (4.69%) and low type of forced smile (10.94%).
In the present study, females displaying natural smile showed a much higher percentage of high (20.3%)and average (30.5%)types of smile line compared to males who had only 4.9% of high and 21.6% average types of smile line.Maximum males had low type of smile line (72.5%).This finding was similar to other studies by by Mark et al 11 and Garg et al. 12 Another study by Sereen et al revealed that females exhibited higher smile line and very high smile line (51.7% and 37.8% respectively). 10Overall, Low type of smile lines were a masculine characteristic whereas high type of smiles were a feminine trait.As the present study was cross-sectional institutionalbased study with convenience sampling procedure; there could be a selection bias.For further research, longitudinal studies with a larger sample size and randomization among general population would be recommended.

CONCLUSION
Overall, females have significantly more periodontal visibility when compared to males during forced smile.
This study highlights various types of smiles on the basis of gender and age in a Nepali population sample.Smile line can be used as a valid tool to assess the esthetic appearance by orthodontists and other clinicians.

Figure 2c :FigureFigure 2b: Class 2 (
Figure 2c: Class 3 (Average smile line) Figure 2d: Class 4 (Low smile line) photographs with the resolution of 18 Megapixels, 7.5X zoom, 18-135mm (29-216mm eq) lens.Two different sets of photographs were taken of each participant in natural and forced smile position.The photographs were standardized as per Liebart et al; 8 by positioning the headrest in Frankfort horizontal plane assuring for proper angulations at a fixed distance of 30 cm.Photographs were evaluated by 3 examiners and findings were recorded.The whole procedure was blinded.Data analysis was done using SPSS 20.0 software.Chi square test was performed to analyze statistical difference between the groups.The level of significance was set at p<0.05.

Graph 1 :
Distribution of subjects according to the classification of natural and forced smile (%) Graph 2: Distribution of natural smile line according to gender (%)

5: Distribution of forced smile line according to age group (%)
13pkota B, Srivastava S, Koju S, Srii R: Evaluation of Smile Line in Natural and Forced Smile Position: An Institution-based Study Sapkota B, Srivastava S, Koju S, Srii R: Evaluation of Smile Line in Natural and Forced Smile Position: An Institution-based StudyDISCUSSIONThe classifications of smile line by Tijan et al5did not specify the type of smile and Jensen et al13only evaluated the natural smile.Therefore, the classification by Liebert et 9rthodontic Journal of Nepal, Vol. 7 No. 1, June 20179Another similar study by Sereen et al in Saudi years participants had 40.5% low type and 37.8% average type of smile, and >51 years participants had 22.2% low type and 48% average type of smile.In age group 18-35 years, a much higher percentage of high (28.2%)and very high (16.7%)type of smile were noted.In comparison with Liebert's study; 8 normal smile had similar findings to our study but differed in forced smile, on agewise analysis.