The smile plays an important role in facial expressions. It affects a person's perception of attractiveness and it is a basis of social interactions (1). Dental esthetics has always been a subject of debate, since it is a well-known fact that beauty lies in the eye of the beholder, but it can vary from person to person, depending on their experience and socio- economic status and education (2, 3).
The size and shape of the anterior upper teeth plays an important role in dental esthetics and smile esthetics (4). In their research, Anderson et al. (5) showed that orthodontists and dentists prefer rounder teeth in women, while persons in general population did not notice the difference in the form of the teeth. On the other hand, all examiners considered the square-oval teeth to be more suitable for a man's smile. It is evident that the individuals belonging to general population do not have a clearly formulated opinion –their attitude toward the form of the teeth is neutral and they do not consider the form of the teeth to be particularly relevant to the esthetics of the smile, whereas the professionals are well aware of the importance of the form of visible teeth and its impact on the general impression of the smile.
In addition to the shape and size of the upper anterior teeth, the relationship between the teeth and dental arch has a very important role in dental esthetics, wherein its most important aspect is the ratio of incisors and canines (1). This relationship is based on the theory of golden proportions (the golden section) and dynamic symmetry (6). The concept of the golden proportions theoretically determines the ideal size of the teeth in their relation (1: 0.681) (2, 3).
Kokich et al. were the first to begin the exploration of differences in the perception of orofacial structures, such as different perceptions of the smile, as beautiful and less beautiful (7, 8). Their research showed that the level of education of dentists affected the perception of the beauty of teeth and smiles, while individuals belonging to the general population exhibited the least amount of criticism.
In his study on perception of asymmetry of the gingival margin and of the shift of the middle arch (9), Pinho has complemented the above mentioned research by including specialists in prosthodontics, along with the general population and specialists in orthodontics. The results showed that the orthodontists observed the shift of the middle arch of just 1 mm, the prosthodontists of 3 mm, while the general population did not even notice the shift. The asymmetry of the gingival margin of only 0.5 mm was visible to the dentists, while individuals belonging to the general population noticed the asymmetry only when it exceeded 2 mm.
It is interesting that in the most of the previous researches not much attention has been given to the specialists in prosthodontics, hence failing to get an insight that would improve the knowledge on their perception of dental esthetics.
Ker et al. (10) based their research on computer manipulation of a photo of a part of the lower third of the face, and they wanted to determine the range of variation which was accepted by patients and, also, to determine to what extent the patients found those images acceptable. The aim of this study was to record the boundary between the ideal and the acceptable smile. The results showed that individuals belonging to general population recognized a perfect smile, but that the range of acceptable variations was wide. The research conducted by Rodriques et al. also confirmed those findings (11).
As for the differences in perception according to gender, the results of Philips et al. (12) showed that there were significant differences in the evaluation of buccal corridors and attractiveness of the smiles between male and female individuals. In other words, men were more tolerant to small / moderate buccal corridors than women. The influence of gender was also visible in the research on the impact of gender differences in perceptions of orofacial variations. Based on the results of the research, Geron and Atalia (13) concluded, that women were more tolerant to the visibility of the gums in the smile.
A large number of studies on smile esthetics are based on data collected from the subjects from general population and on data collected from the dentists with various educational backgrounds. Therefore, Žagar and Knezović (14) included some patients who were to estimate the esthetics of their teeth and the surrounding soft structures of their smile. The results have shown that women focus more on details, which can be helpful in making prosthetic replacements and developing guidelines for esthetic rehabilitation of the anterior teeth and their surrounding structures.
All of the above references are based on different criteria of assessment (diverse scales: dichotomous, Likert, etc.) and on various issues. A unique questionnaire (Orofacial Aesthetic Scale) comprising 8 questions relating only to the esthetics of the orofacial region has recently been introduced. Larsson introduced this questionnaire into dental research and pointed out to its excellent psychometric properties (15, 16). In the Croatian cultural environment, Peršić et al. translated and examined the same questionnaire and it was shown to have satisfactory characteristics (17).
The purpose of this paper was to carry out a study with the following goals:
to determine whether there was a statistical difference in perception of anatomical variations of the anterior teeth and the surrounding structures between two groups of assessors, those from general population and the dentists,
to determine whether there was a statistical difference between the three groups of assessors (general population, doctors of dental medicine and specialists in prosthodontics), or rather to determine the difference in their perception of anatomical variations of the anterior teeth and their surrounding structures,
to determine whether there was a significant difference in the assessment of the perception of anatomical variations of the anterior teeth and the surrounding structures based on gender of the assessor,
to determine whether there was a significant difference in the assessment of the perception of anatomical variations of the anterior teeth and the surrounding structures based on the age of the assessor.
The hypothesis of this research was that general dentists and prosthodontists gave lower scores than the individuals from general population when it came to deviations from the ideal characteristics of the teeth and the surrounding structures.
Material and Methods
The research included 60 patients who voluntarily participated in the study. The participants were mainly young people (19-40 years old). Since the criteria of the research were to have a permanent fully* toothed dentition (excluding third molars) and mostly intact upper front teeth, all respondents belonged to Angle class I, and only a mild rotation of the teeth or compression were allowed. All potential subjects with gingival inflammation and hyperplasia, those with more severe gingival recession, the subjects with periodontal-surgical procedures in the top front intercanine area, or those with fillings or crowns and traumatic injuries were excluded from the study.
The patients were informed about the purpose and the method used in the research and they gave their written consent. The patients were explained that the research posed no threat to their health and that it was to be carried out in accordance with ethical principles and the Geneva Convention. The data were anonymous. Each participant could have withdrawn from the study at any time. The Ethics Committee of the School of Dental Medicine approved the study.
Immediately prior to taking digital photographs, the female subjects removed traces of makeup from their lips and male respondents shaved, thus enabling the assessors to see their teeth and lips on the digital photographs. In the course of taking the photos, each subject was sitting in the dentist's chair in an upright position, holding the head upright and looking straight ahead with lips opened wide into a smile. The research consisted of taking pictures of the anterior teeth and the lips of subjects who smiled and of the lower third of the face in the duration of 10 minutes.
The front teeth of each subject were photographed using a digital camera NIKON, 14.0 Mega Pixels, COOLPIX S3100 (Tokyo, Japan) from a standardized and advance-marked distance of 10 cm, at the height of the front teeth of each of the respondents.
All digital images were stored on a Memory Stick EMTEC 8 GB (Nikon, Tokyo, Japan), and then arranged on a few A4 photo papers (FUJI COLOR CRYSTAL ARCHIVE PAPER, FUJIFILM Holdings Corporation, Tokyo, Japan) and developed. On each photo paper (template), there were 8 photos with precisely indicated number of the patient so that assessors would not confuse them when filling the tables.
The collected photos were then assessed by 21 individuals from the general population (who were neither trained to work in a dental office nor to perform tasks related to dentistry and who were not previously included in the study), 20 graduate dentists and 20 specialists in prosthodontics.
Using a part of the questions from the OAS questionnaire (Orofacial Aesthetic Scale, see Annex) the esthetic characteristics of the teeth and the surrounding anatomical structures on the photographs were assessed in duration of 60 minutes. The Croatian version of the OAS questionnaire was translated from the original English version (17). Looking at the pictures of smiles of the patients, the assessors rated them on a scale from 1 to 5 (1 = completely dissatisfied, 5 = completely satisfied). This rating scale from 1 to 5 is an acceptable method of assessing in the Croatian cultural environment. Questions under the number 1 and 2 from the OAS questionnaire were not used.
A statistical analysis was performed using the statistical program SPSS 17 for Windows (Chicago, Illinois, USA), and it included a one way Kolmogorov - Smirnov test for normality of distribution, descriptive statistics, the t-test for independent samples, methods of parametric statistics for testing the significance of differences – one way ANOVA, Scheffe post hoc tests and ANOVA test with 3 factors.
Table 1 shows the descriptive statistics of the assessment of questions from the OAS questionnaire and the arithmetic mean of summed scores based on the group of assessors (general population (n = 21) and dentists (n = 40)). It also presents the results of testing the significance of difference between the assessments of the general population and that of the dentists (t-test for independent samples).
** There is a statistically significant difference between the general population and the dentists (p<0.001)
Assigned ratings were significantly higher in the group of dentists for all questions, except for the assessment of appearance of gums (p <0.001) (Table 1); the general population estimated gums to be more esthetically pleasing compared to the dentists.
Table 2 shows the descriptive statistics of the assessment of questions from the OAS questionnaire and the arithmetic mean of summed scores based on gender of the assessor. It also presents the results of testing the significance of difference in ratings by male and female assessors (t-test for independent samples).
** There is a statistically significant difference between the genders (p<0.001)
Male assessors gave significantly higher scores in assessing the appearance of the gums, the general appearance of the lower third of the face, mouth and teeth, and in the arithmetic mean of summed scores (p <0.001) (Table 2). In other words, male assessors evaluated them as esthetically more pleasing compared to female assessors, who were particularly sensitive to the appearance of gums.
The significance of difference in scores between the three groups of assessors (general population, general dentists, and specialists in prosthodontics) was tested by a one-way ANOVA test and it is shown in Table 3. It was found that there was a statistically significant difference in scores between different groups of assessors (p <0.001, Table 3). In order to determine which group was responsible for a statistically significant difference, the Scheffe post-hoc tests were conducted.
Descriptive statistics of the assessment in all three groups of assessors (general population, general dentists, and specialists in prosthodontics) is shown in Table 4, together with the results of Scheffe post hoc testing. Post-hoc tests showed that the specialists in prosthodontics gave significantly higher scores (appearance of the mouth, dental arches, teeth shape, teeth color and general assessment of the lower third of the face). Post-hoc tests also showed that the assessors belonging to the general population gave significantly higher scores to the visibility of the gums (p <0.05, ** p <0.001), while the prosthodontists gave worst marks.
The significance of difference in assessment between the three groups of assessors based on their age (<35, 36-55, >56) was tested by a one-way ANOVA test and is shown in Table 5. In order to determine which group is responsible for a statistically significant difference, the Scheffe post-hoc tests were conducted.
Descriptive statistics of the assessment for all three groups of assessors based on their age (<35, 36-55,> 56) is shown in Table 6, together with the results of Scheffe post hoc testing. Post-hoc tests showed that older patients assessed visible gums with significantly higher scores, while they gave significantly lowest scores to dental arches (p <0.05, ** p <0.001)
The whole model that includes factors of age, gender and profession interprets the dependent variables (grades of esthetics) as only 18.2% (R˛=0.182).
In their approach to the esthetics of teeth, dentists are led by pragmatic principles of achieving symmetry and improving facial appearance. In the course of denture fabrication, a dentist tries to satisfy the patient's vision of the esthetic appearance of the denture, but unfortunately, it often happens that their perception of what is esthetically pleasing differs significantly (18). It should also be pointed out that there is a series of social, cultural and psychological factors that are not yet fully understood, but which can affect the definition of the ideal in esthetics in a given population (19).
Most of the research on this topic takes into account the general population, general dentists and specialists in orthodontics, while there are a small number of studies including specialists in prosthodontics, which is important since the fabrication of dentures represents a high percentage of all dental procedures.
This research has shown a statistically significant difference in the results (scores) among the general population, general dentists and specialist in prosthodontics, or rather it has determined the difference in their perception of anatomical variations of the front teeth and the surrounding structures by taking into account the age and the gender of the assessor.
Comparing the general population and the dentists, the dentists' ratings were significantly higher for all questions, except for the assessment of the appearance of gums (p <0.001) (Table 1). The general population estimated the gums to be more esthetically pleasing compared to the assessment of the dentists. These data can be interpreted based on the fact that dentists, especially specialists in prosthodontics, give higher grades to natural looks, while the general population aspires to the ideal esthetics of teeth, probably due to the influence of media. In contrast, individuals belonging to general population pay less attention to the gums, which are not so visible at first glance, hence being less important to them, while dentists are aware of the role of gums and include this parameter in their assessment, and are very critical of it.
Periodontists were considered to be most critical to the appearance of gums, which can be the topic of further research.
The analysis of the data according to gender of the assessors (Table 2) points to somewhat higher ratings and greater tolerance of male assessors. The female assessors were expected to be more critical to the esthetics of the teeth.
The comparison of assessors according to their age (<35, 36-55,> 56) has shown that the middle-aged group gave highest scores, except for the gums where the highest scores were given by the oldest group of respondents (Table 5). The result can be explained by the fact that younger people are more critical since they have not yet had big problems with their teeth; hence, their attention is focused solely on the esthetics of the teeth. The oldest group of respondents gave the highest scores to the gums, which points to the fact that they are the least important to them in the esthetics of the orofacial region.
Based on the results, we concluded that respondents from the general population group gave lower scores to the orofacial esthetics than dentists, except for the appearance of the gums which got lower scores by dentists. General dentists gave lower scores to the shape and color of teeth, appearance of dental arches and lips, and general appearance of the lower third of the face than prosthodontists. Prosthodontists were also more tolerant towards deviations from the "ideal esthetics" and more critical in assessing the appearance of the gums than general dentists. Female respondents were more critical in estimating the appearance of the gums. Middle-aged assessors (36-55 years old) gave the highest scores to the esthetics of the shape and color of the teeth, the appearance of dental arches and lips and the general appearance of the lower third of the face. The respondents belonging to the oldest group gave the highest scores to the appearance of the gums.
Since patient satisfaction is assumed to be an important indicator of quality of care, our research may help dental practitioners and prosthodontists to plan such a prosthetic therapy which would also meet the patient’s criteria.