The literature offers limited and even conflicting information on the etiology of gummy smile. Therefore, this study aimed to evaluate smile line, hypermobile upper lip (HUL), altered passive eruption (APE), and short upper lip (SUL) distribution in a group of patients seeking dental treatment and to examine their effects on gummy smile. A total of 501 individuals (265 men, 236 women) were included in the study. The patients were grouped by gingival display, and presence of HUL, APE, and SUL were evaluated. Multivariate Logistic Regression analyses were performed to investigate the impact of possible risk factors on gummy smile. Of the individuals, 173 (34.5%) had a low smile line, 127 (25.3%) had an average smile line, 146 (29.1%) had a high smile line, and 55 (10.9%) were gummy smile patients. Individuals with gummy smile were younger than the individuals with low smile line (P < .001). As for the possible risk factors for gummy smile, age (odds ratio [OR]: 0.936; 95% CI: 0.901 to 0.972; P = .001), HUL (OR: 18.85; 95% CI: 7.82 to 45.44; P < .001), and APE (OR: 8.819; 95% CI: 3.894 to 19.973; P < .001) were found to be significant together. Gender and SUL/upper lip length were not found to have any impact on gummy smile. HUL is the primary factor that increases the probability of having gummy smile, followed by APE as the secondary factor. It seems reasonable to focus on correction of the HUL for treatment in most gummy smile patients.
