Landmark movement trajectory: A simple reference to understand the dominant muscle contraction in a dynamic smile expression

The Underappreciated Role of the Platysma Muscle in the Perioral Expressions in Young Adults

BACKGROUND

The platysma is involved in lower face movement, yet limited information on its functional role when making perioral expressions is available.

OBJECTIVES

The aim of this study was to use 3-dimensional (3D) photogrammetry to analyze platysma activity when making expressions.

METHODS

Standardized frontal-view 3D images were obtained from 54 volunteers. Three perioral expressions were analyzed: a full smile, mouth corner depression, and a grimace to show the lower teeth. Positive volume change in the "heat map" of the neck skin surface-determined by the superimposed image subtraction technique-served as a sensitive indicator of platysma contraction.

RESULTS

When making the 3 expressions, the proportions of platysma contraction were 42.6%, 75.9%, and 92.6%, respectively. The platysma worked as a more critical dynamic force than expected. In most smiles involving the platysma, its upper portion contracted. With the laterally downward traction on the lower lip increasing, the upper and lower portions of the platysma contracted together and formed muscular bands. The platysma contracted extensively in the other 2 expressions. In some cases, platysma bands were observed to form due to vigorous contraction of muscle fibers. In addition, the platysma was found to be highly functionally active in young individuals.

CONCLUSIONS

This study introduced a simple method that can sensitively identify the functional status of the platysma. The results showed the platysma's highly active function in perioral expressions in young adults. These findings may assist surgeons in personalized decision-making toward platysma muscle-weakening strategies and work as an objective tool for outcome evaluation.

LEVEL OF EVIDENCE: 4