Date: July 2026.
Source: Scientific Reports, DOI: 10.1038/s41598-026-61230-1.
Abstract: Lip incompetence is an esthetic orthodontic problem, but its functional relevance during mastication remains unclear. This study aimed to develop an objective system for assessing three-dimensional facial dynamics during mastication and to compare facial soft-tissue coordination and lip-closure force between individuals with and without lip incompetence. Thirty-nine children aged 6–12 years were classified into a lip-incompetence group (n = 16) and a control group (n = 23). Participants chewed gum unilaterally while 3D facial images were recorded. A homologous wire-mesh model was generated for each frame, and elastic energy based on inter-point displacement was calculated for the upper and lower lips. After regional averaging and normalization, the time-integrated difference between normalized mean elastic energies of the upper and lower lips was defined as the Surface Synchrony Index (SSI), representing lip-movement coordination rather than strict temporal phase synchronization. Lip-closure force was also measured. SSI was significantly higher in the lip-incompetence group than in the control group, indicating reduced coordination between upper and lower lip movements during mastication. In contrast, no significant difference in lip-closure force was observed between groups. These findings indicate that lip incompetence was associated with impaired coordination of facial soft-tissue movements during mastication. Static observation and lip-closure force alone are insufficient to evaluate functional problems during mastication. Surface-based kinematic indices enable objective assessment of difference in facial soft-tissue coordination associated with lip incompetence and may provide clinically relevant information for functional evaluation.

Experiment 1: Facial Morphospace: A Clinical Quantitative Analysis of the Three-Dimensional Face in Patients With Cleft Lip and Palate. Chihiro Tanikawa

Article: Three-Dimensional Analysis of Facial Soft-Tissue Movement During Mastication in Children With Lip Incompetence.
Authors: Namiki Nagata, Chihiro Tanikawa, Takashi Yamashiro. Dept. of Orthodontics and Dentofacial Orthopedics, Graduate School of Dentistry, Osaka University, Osaka, Japan.

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