# Thermographic Behaviour of the Orbicularis Oris Muscle Under Different Provocative Tests

## TL;DR

This study uses infrared thermography to show how the orbicularis oris muscle heats up during different tasks like chewing and sustained contraction.

## Contribution

The study introduces a method to assess muscle activity through thermography during specific facial muscle tasks.

## Key findings

- The orbicularis oris muscle showed significant temperature increases during chewing and contraction tasks.
- A 2-minute rest interval between tasks was insufficient to return muscle temperature to baseline.
- Temperature changes were consistent across different chewing materials and contraction types.

## Abstract

Infrared thermography is an objective method for investigating muscle functioning, enabling inferences about physiology and therapeutics. This noninvasive and non‐ionising imaging diagnostic method allows real‐time visualisation of the vascular and musculoskeletal systems through skin microcirculation dynamics. It transforms information about the human body's thermal radiation, captured via infrared radiation, into an analysable image.

To describe the thermographic behaviour of the orbicularis oris muscle during sustained contraction and chewing tasks.

The study included 56 healthy women aged 18–52 years, who underwent thermographic evaluations before, during, and after performing sustained contraction and chewing tasks. The orbicularis oris muscle was analysed qualitatively and quantitatively using anatomical thermal areas and Student's t‐test to compare mean temperature data.

Qualitative analysis revealed temperature changes during the provocative tasks. A comparison of mean temperatures showed a significant temperature increase, corroborating the qualitative findings. The mean temperature variation per task was as follows: 0.57°C during lip compression, 0.20°C during lip protrusion, 0.57°C while chewing peanuts, 0.43°C while chewing crackers, and 0.37°C while chewing a bread roll. There was a decrease in mean temperature during the intervals between tasks, though insufficient to return to baseline levels, indicating a cumulative temperature effect between tasks.

The orbicularis oris muscle temperature increased during the provocative tasks. The 2‐min interval between tasks was insufficient for the resting temperature to return to baseline levels. These findings confirm that thermography is an effective method for identifying such temperature changes.

Study design showing the thermographic region of the orbicularis oris muscle (Picture 1), the foods used for chewing and the increase in mean temperature after the provocative tests (Picture 2).