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Related Experiment Video

Updated: Jul 18, 2026

Single-stage Dynamic Reanimation of the Smile in Irreversible Facial Paralysis by Free Functional Muscle Transfer

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Published on: March 1, 2015

The spontaneous smile in dynamic motion.

Vicky V Tarantili¹, Demetrios J Halazonetis, Meropi N Spyropoulos

¹Orthodontic Department, Dental School, University of Athens, Greece.

American Journal of Orthodontics and Dentofacial Orthopedics : Official Publication of the American Association of Orthodontists, Its Constituent Societies, and the American Board of Orthodontics

|July 20, 2005

Summary

The dynamic nature of spontaneous smiles, analyzed through facial measurements and time-graph plots, reveals a staged progression. This complexity challenges the reliability of static images for aesthetic evaluations.

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Area of Science:

Human facial expression analysis
Child psychology
Biomechanical analysis of facial movements

Background:

Understanding the dynamic characteristics of spontaneous smiles is crucial.
Previous research often relies on static facial captures, potentially oversimplifying smile dynamics.

Purpose of the Study:

To record and analyze the dynamic temporal features of spontaneous smiles in children.
To investigate the distinct phases and movement patterns within a natural smile.

Main Methods:

Utilized hidden cameras to film 15 children (average age 10.5 years) watching a humorous video.
Digitized video frames to construct time-graphs and plot mouth point movements.
Analyzed facial measurements including upper lip elevation and mouth width changes.

Main Results:

Spontaneous smiles exhibited a staged progression: an initial attack phase (average 500 ms), followed by a sustaining phase with waxing and waning, and a fade-out stage.
Facial measurements indicated significant upper lip elevation (28%) and mouth width increase (27%).
Mouth corners moved superiorly and laterally at approximately 47 degrees, with variable durations for later stages.

Conclusions:

The complex, staged dynamics of spontaneous smiles question the validity of single photographic captures for aesthetic assessment.
Findings suggest that dynamic smile analysis is essential for accurate treatment planning in fields like orthodontics and cosmetic dentistry.