The Effect of Anterior Teeth Forms in Smile Esthetics

Background and objective: Smile play a great role on the face attractiveness. A good-looking smile advances the individual’s acceptability by affecting the social interactions. This study aimed to evaluate the effects of different anterior teeth forms on smile esthetics in people referred to dental faculty clinic in Ardabil, Iran. Materials and methods: For this survey, six photos of different shapes of central and lateral incisors (round, round-square, and square), and canines (pointed and flat) were shown to 469 people in the dental faculty of Ardabil, Iran, including 248 females and 221 males. Each image was scored from one to ten. Results: According to this study, no significant difference was observed between age, gender, and educational stage of participant (P>0.05). According to the groups judgments, the scores of images of pointed tip canine and round incisors and flat canine and round incisors were the highest and the images of pointed tip canine and square incisors and flat canine and square incisors were scored the least. Regarding the results of the Wilcoxon test, the pointed canine type was not effective in the esthetic judgment. The participants similarly rated the photos of pointed and flat canines (P>0.05). Conclusion: The age, gender, and educational stage was not correlated to the preferences about esthetics of the aforementioned photos. Generally, the smile with anterior teeth with round incisal edges was preferred.


Introduction
Esthetics in modern dentistry has become increasingly important [1]. Face is the most important part of the people's physical appearance and mouth is the basis of facial attractiveness [2]. The number of individuals seek to improve the form of anterior teeth is tend to grow continuously.
Nowadays, the focus of dentistry procedures has shifted to enhancing the dental appearance. Because it is known that the face attractiveness plays an important role in social interactions, academic achievement, occupation promotion, and even family satisfaction [3].
"Smile" is the aesthetics index of face, which is related to dentistry field. All dentists might offer smile modification as one of their services. A beautiful smile has several psychological effects including improvement in individual's self-image and confidence [4]. Various studies are conducted on assessing the different aspects of a beautiful smile [5]. Carolien Rieffe evaluated the effect of extra-oral factors on face esthetics; furthermore, the internal ones are also investigated in various studies.
In a study conducted by Bothung et al. the effect of inclination of upper maxillary canines has been evaluated [6]. Hideki Ioi et al. demonstrated the effect of vertical positions of anterior teeth on smile esthetics in South Korea and Japan [7]. Therefore, the anterior maxillary teeth form considered as one of the most substantial aspects of smile esthetics; it is in line with the study conducted by Ong et al. which indicated that the anterior teeth form has the highest impact on the smile attractiveness [8]. Various forms of anterior teeth have been investigated in several studies. For instance, Williams et al. have submitted the categories of diverse forms of anterior teeth [9,10].
Ahmed Hussain et al. have evaluated the influence of various maxillary incisor shapes on perceived smile esthetics [11]. Maria Eduarda has compared the esthetics perception in different groups of regular and orthodontic patients and orthodontists by reconstruction of incisal embrasures in different forms (round, semi-round, and square) by changing the area of adjacent gum [12].
This study aimed to evaluate the effect of anterior teeth forms on perceived smile esthetics by referring people to the dental faculty clinics of Ardabil, Iran, 2016.

Materials and Methods
This descriptive cross-sectional study investigated the general perspective about the natural smile. For uniformity and ruling out the interfering factors, only the smile frame, consisted of teeth, lips, and the surrounding skin was considered in these photos; the necessary alterations were performed using Adobe Photoshop version CS5.

JBR Journal of Interdisciplinary Medicine and Dental Science
Six photos with different forms of anterior teeth were separately demonstrated in two pages (Figures 1 and 2). The photos of the pointed tip canine and round incisors, pointed tip canine and roundsquare incisors, pointed tip canine and square incisors, flat tip canine and round incisors, flat tip canine and round-square incisors, and flattip canine and square incisors were demonstrated in six figures, respectively.  Each photo was showed to 469 patients referred to dental faculty clinic in Ardabil, Iran in two groups of 248 females and 221 males. They scored the photos between 1-10, and then information forms were completed.
The esthetics of each photo was evaluated based on the visual analogue scale (VAS), that its validity and reliability is confirmed by the literature [13].
Data analysis was performed using SPSS software version 16, Friedman, Kruskal-Wallis, and Wilcoxon tests. In all measurements Pvalue less than 0.05 was considered statistically significant.

Results
Since our data were ordinal, the median was measured to reveal the central distribution (Tables 1 and 2). The results of Kruskal-Wallis test determined no significant difference in the terms of esthetics judgments between both groups of men and women (P>0.05).
According to the results of Kruskal-Wallis test, there was no significant relationship between the age and educational stage of participants and their esthetics judgments (P>0.05). Given the results of Friedman test, a significant disparity was observed between the awarded scores of each photo (P<0.05).
Thus, the Wilcoxon test was applied to determine the differences between the groups (Tables 3-8). The first and forth images were given the highest and the third and sixth ones were given the least scores among the groups.            Regarding the results of the Wilcoxon test, the canine cusp tip did not affect the perceived esthetics. According to Listener's test, there was no diversity between the scores given to the images showing round edges of incisor, central, and lateral teeth in two groups of sharp and smooth canines (P>0.05). Additionally, no significant difference was reported between the scores given to images with edges of incisor, central, and lateral teeth with round-square case in comparison to incisor, central, and lateral teeth with square case in two groups of sharp and smooth canines (P>0.05).
Regarding the Listener's test, more points were given to the images with edges of incisor, central, and lateral teeth with round-square case rather than square case (P>0.05). Considering the educational stage, people with high school diploma and higher education degree (bachelor or above) who aged between 30 and 45 gave similar scores to the images.

Discussion
In the current study, the photos of different smiles were shown to the participants who were placed in two groups of diverse ages, genders, and educational stages in dental faculty clinics, Ardabil, Iran. The only difference between the images was in terms of the edges of maxillary anterior teeth. In this study, the participants were categorized based on the need for the probable treatment. People aged from 15 to 30, 30 to 45, and 45 to 60 needed orthodontic, esthetics, and prosthetic treatments, respectively. Since the culture and personal fields of the observers influence the esthetics perceiving, the participants were categorized in two groups with academic and nonacademic degrees to assess the possible impact of the educational level.
According to Phillips study, the anterior teeth form has a great effect on smile esthetics [16].
Regarding the Goldstein's study, teeth form and the smile arc are the substantial elements of the golden proportion in relation to their size [17]. Given the study conducted by Ong, an attractive smile is formed with combination of various factors and the anterior teeth form is the most important one of them [8]. In this study similar to the literature, VAS method was applied to evaluate the smile esthetics [18,19].
Given the results of another study, all the groups with different genders, ages, and educational stages similarly gave the most score to the teeth with round edges; however, the canine teeth form was not effective. This finding was consistent with the results of Anderson, which announced that the different canine teeth forms have lower impact on esthetics in comparison to the anterior teeth form. Therefore, in many cases, canine teeth reformation is not recommended due to the lower impact on the esthetics and functional considerations.
After evaluating the effectiveness of the rounded edge teeth on esthetics, the participants scored the best to the teeth with roundsquare form and then to those with square edges. According to Heravi et al. study, the lay people preferred the teeth with rounded edges more than the other forms. In this study, individuals age and gender had no impact on their judgement [18]. In Maria study, people preferred the incisal semi-rounded edges [20].
Jannike Jantung have compared the esthetics perception between dentists and ordinary people, and concluded that the ordinary people and dentists' idea are different in terms of esthetics [21]. In our study, gender did not have influence on judgment of esthetics. According to Brisman study, gender was effective in esthetics judgement, women preferred anterior teeth with rounded edges, and men preferred those with square edges. The judgment of esthetics is a subjective and conceptual issue, since it is affected by cultures, traditions, and historical background in each society.
The reported conflicts in various studies could be related to the cultural and historical differences in the evaluated society. Esthetics judgments varies over time and can be influenced by media; furthermore, more studies on esthetics judgments are recommended in different communities.

Conclusion
Regarding the results, different ages, genders, and educational stages had no impact on the esthetic judgements. People preferred rounded incisal edge form more than the other ones and the diverse forms of canine teeth had no effect on smile esthetics judgements.