Evaluation of aesthetic criteria and limitations in the smile zone

The dentist should be able to apply a functional and aesthetic treatment by combining subjective aesthetic perception with concrete scientific criteria. The aim of this study was to evaluate whether changes in lower incisors visibility, smile line and lower lip alignment, buccal corridor, upper gingival visibility and depth of embrasures make a difference between prostodontists, senior dentistry students and laypersons in terms of aesthetic perception. Intraoral photographs and frontal smile photographs taken from a male and female model without restoration in the smile area were standardized by combining them digitally. On the internet, www.freeonlinesurveys.com, a 13-question questionnaire was created and participants were asked to select only one of the visuals in response to the question 'which smile is best for you?'. In the survey; The effects of lower incisors visibility, smile line and lower lip alignment, buccal corridor, upper gingival visibility and depth of embrasures on aesthetic perception were evaluated. 148 prostodontists, 245 dentistry students and 147 laypersons participated in the study. The distribution of the responses given in terms of aesthetic appearance between the groups was analyzed statistically using the Likelihood Ratio test, Pearson's Chi-Square, Fisher's Definitive Probability Test, Continuity Corrected Chi-Square Test and Pearson's Chi-Square Test.(p <0.05) McNemar test was used to evaluate the significance of differences between groups in terms of aesthetic response to female and male images.(p <0.05) Correct answers determined by examining previous studies and prosthodontists were the best performing group. Aesthetic criteria are perceived with higher accuracy in female model images compared to male model images. High visibility of the lower incisors was the least favoured option by all three groups regardless of model gender. It was observed that the changes in the amount of buccal corridor did not make any difference in aesthetic perception. Reverse smile line and lower lip alignment were not aesthetically pleasing for all attendants. While images with normal upper gingival visibility were perceived more aesthetically in the female model, a common aesthetic perception between the male images could not be concluded. In the question about the depth of the embrasure, normal depth was perceived as more aesthetic in the female model, while the shallow embrasure depth in the male model was evaluated more aesthetically by all groups. The results obtained in the simulation of cosmetic treatment applied to the images to reduce the visibility of lower incisors showed that reducing the lower incisor visibility affects the aesthetic perception positively in both female and male models. This study was approved by Baskent University Institutional Review Board (Project no: D-KA19/15) and supported by Baskent University Research Fund. Keywords: Dental aesthetics, smile design, cosmetic treatment