The Effect of Dental Midline Asymmetry and Diastema on Esthetic Perception Among Undergraduate Dental Students: A Survey Study

Abstract

Aim: This study evaluated dental students perception of smile aesthetics regarding midline devia-tion and diastema, and examined differences by gender, prior treatment, and education level. Material and Methods: A total of 550 students were invited, 415 responded, and 400 valid questionnaires (268 females, 132 males) were included in the final analysis. Nine digitally modi-fied images were produced from one facial photograph to show midline deviations (0 mm, 1 mm, 2 mm) and diastema widths (0 mm, 1 mm, 2 mm). Students rated each image on a Visual Analog Scale (0–10). Because the same participants rated all nine images, differences among the nine smile conditions were analyzed using the Friedman test. When significant, post-hoc pairwise comparisons were performed using the Wilcoxon signed-rank test with Bonferroni correction (adjusted α = 0.001389). Between-group comparisons (gender, education level, treatment histo-ry) were analyzed using the Mann–Whitney U test. Results: The Friedman test revealed statistically significant differences among the nine smile conditions (χ² (8) = 2536.21, p < 0.001; Kendall’s W = 0.79), indicating a large effect size. Post-hoc Wilcoxon signed-rank tests with Bonferroni correction (adjusted α = 0.001389) demonstrat-ed that all pairwise comparisons were statistically significant. The control condition received the highest aesthetic ratings (median 8 (7–9)), whereas the lowest ratings were observed for the 2 mm deviation + 2 mm diastema condition (median 2 (1–3)). Conclusion: Even minor midline deviation or diastema reduced perceived smile aesthetics, and combined discrepancies produced the greatest reduction, with the 2 mm deviation + 2 mm dia-stema condition rated the least aesthetic.