Abstract
INTRODUCTION: The rising use of orofacial harmonization highlights the importance of the lip area, closely linked to the orbicularis oris muscle. This longitudinal study assessed the electromyographic (EMG) activity of the upper and lower orbicularis oris muscle in adult women following hyaluronic acid lip filling. MATERIALS AND METHODS: Twenty-two adult women, with a mean age of 35.4 ± 12.3 years, were included. EMG was measured during rest, cheek inflation tasks (concurrently and alternately), lip protrusion and compression, and before, 30, and 60 days after lip filling. Differences were significant using t -test and repeated measures analysis of variance with Bonferroni correction ( p < 0.05). RESULTS: Significant EMG differences were found in the upper orbicularis oris muscle (before vs. 30 days, p = 0.04) and lower orbicularis oris muscle (before vs. 30 days, p = 0.0006) during bilateral cheek inflation, and in the upper orbicularis oris muscle (30 vs. 60 days, p = 0.05) during rest. At 30 days, EMG of both upper and lower orbicularis oris muscle decreased in all tasks. By 60 days, the upper muscle's EMG increased in most tasks, while the lower muscle's EMG decreased during cheek inflation tasks. The lower orbicularis oris muscle had significantly higher EMG than the upper in nearly all tasks ( p = 0.000). CONCLUSION: Hyaluronic acid lip filling initially relaxed the orbicularis oris muscle at 30 days. By 60 days, the upper muscle's activity increased, indicating adaptation, while the lower muscle remained less active during cheek inflation, showing distinct functional changes after 60 days.