Assessing Gingival Smile and Muscle Strength

A gummy smile (GS) may result from dental, skeletal, or muscular etiologies, with lip hyperactivity (LH) being the most prevalent. Currently, lip muscle strength assessment relies on empirical methods, compromising the precision of certain treatments. This study aimed to evaluate muscle strength related to smiling, establish correlations between lip movement and both individual and total muscle force, and determine the prevalence of GS etiologies. A device was developed to measure the strength of each lip muscle during smiling. A total of 89 individuals (mean age 28 ± 8.4 years; 80.9% female) were divided into four groups: G1 - Upper lip hyperactivity (9%); G2 - Dental/skeletal causes (19.1%); G3 - Control (33.7%); G4 - Hyperactivity combined with other etiologies (38.2%). Statistical analysis included ANOVA, Tukey's post hoc, and chi-square tests. LH, alone or combined, was the most prevalent etiology (68.2%) and presented 30% greater muscle strength than other groups. G4 exhibited significantly higher strength across all six muscles evaluated compared to G2 and G3. The zygomaticus major muscle in G1 was significantly stronger than in G2 and G3. Lip translation exhibited significant differences in force based on displacement (p <0.001), with the most substantial force observed from 8 mm of displacement. LH was identified as the primary etiology of GS, with individuals displaying LH showing greater muscle strength compared to other etiologies or controls.