Upper Lip Length and Mobility Differ Between Racial Groups

Objectives: Hypermobile upper lip (HUL) is the most prevalent etiology of “gummy smile”. HUL has been defined based on very limited data on normal upper lip mobility (ULM) during smile, obtained from Caucasian adolescents. Information is lacking on ULM in adults and different racial groups. The purpose of this study was to investigate ULM in adults and explore possible ULM differences between two racial groups.
Methods: A cross-sectional observational study recruited adults (aged 18-41 years) self-identifying as white (Non-Hispanic Caucasian (NHC)) or black (Non-Hispanic African/African-American (NHA)); not of known mixed racial origin; systemically and periodontally stable; normal dimension maxillary anterior teeth; no history of orthodontic treatment, oral or maxillofacial defect/surgery (except for third molar extractions), periodontal surgery on maxillary anterior teeth, previous injectable dermal fillers or botox (≤8 months prior to study enrollment). TULL (=total upper lip length) and ULM (=distance of lip movement during transition from rest to maximum smile over midline) were measured directly (clinically) and on recorded digital photographs. Differences between racial groups and between direct and digital measurements were analyzed by unpaired and paired t-test, respectively.
Results: Fifteen NHC and 15 NHA consented females completed study protocol. Average participant age was 23.5±4.9 years, with no inter-group differences (p=0.914). TULL differed significantly between the groups, for both direct (NHC=21.1±2.3mm, NHA=24.7±2.3mm; p<0.0003) and digital (NHC=20.7±2.5mm, NHA=24.2±2.1mm; p<0.0004) measurements. Similarly, ULM differed significantly between groups, for both direct (NHC=5.7±1.3mm, NHA=8.1±0.9mm; p<0.0001) and digital (NHC=5.4±1.6mm, NHA=7.3±1.4mm; p<0.0013) measurements. For the entire study population (n=30), there was a strong positive correlation between direct and digital ULM measurements (r=0.87). However, direct measurements were significantly greater than digital measurements (p=0.0028).
Conclusions: These novel results on upper lip length and mobility in adults and in different racial groups indicate that both upper lip length and mobility are significantly greater among African/African-American compared to Caucasian adults.