Three-dimensional analysis of nasolabial fold displacement during smiling: An evaluation of positional changes, segmental variations, and clinical implications

ÖZSOY U., ALKAN E., YILDIRIM Y., Yılmaz B., ÖZSOY Ö., Yüksek H. E.

Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology, 2026 (ESCI, Scopus)

Özet

Objective: The nasolabial fold (NLF) is a key facial structure involved in expressions and aesthetics, with its movement playing a critical role in clinical and surgical applications. This study aims to analyze the NLF's three-dimensional (3D) movement during smiling, assessing segmental variations and differences based on sex and facial side dominance. Methods: Twenty healthy volunteers (10 males, 10 females) aged 18–23 years participated. Facial movements were recorded using a BTS SMART DX100 motion capture system with markers along the NLF. Participants performed a Duchenne smile five times, and angular and linear displacements in cranial, lateral, and dorsal directions were calculated. Statistical tests assessed differences between movement directions, sexes, and facial sides. Results: Cranial displacement (14° ± 5°) was the most significant, followed by lateral (12° ± 5°) and minimal dorsal displacement (5° ± 3°). The upper and middle thirds exhibited the most cranial movement. No significant differences were found between sexes or facial sides. Expressed linearly, the NLF points shifted by 7–15 mm (whole-fold mean 11.6 mm), the displacement being greatest near the mouth corner; dorsal motion was angularly small but linearly substantial, indicating that angular and linear measures capture complementary aspects of the movement Conclusions: Analyzing the NLF's sub-segments enhances the understanding of localized muscle and tissue interactions, supporting more precise therapeutic and clinical applications. The findings highlight the importance of advanced analytical methods for improving diagnostic accuracy and facial biomechanics research.