Proposal of a protocol for thermographic assessment of the orbicularis oris muscle

Background The orbicularis oris muscle is extremely important to performing various oral functions, including mastication, swallowing and speech. Infrared thermography is a non‐invasive painless technique that does not require either contrast or ionisation. It has been increasingly used in speech‐language‐hearing therapy in the last years. Objective The objective of the study was to propose a thermographic analysis method for the orbicularis oris muscle. Methods This is an observational, analytical, cross‐sectional study. The area of the orbicularis oris muscle was defined based on its anatomy with thermographic images of 11 children and 13 adults. Then, this area was divided into four quadrants, each of which was analysed considering four different shapes: a triangle; a rectangle; a triangle with a rounded side, including the vermilion zone; and a customised shape encompassing only the region of the orbicularis oris muscle, not including the vermilion zone. Data were collected and analysed with the coefficient of variation and interrater agreement. Results Data variability for the four shapes had similar dispersions per region of the orbicularis oris muscle, in both maximum and mean temperatures and in both children and adults. The rectangle was the shape with the lowest coefficient of variation in more regions of both adults and children. Interrater agreement was excellent for all shapes, in both children and adults. Conclusion Currently, the best way to analyse the orbicularis oris muscle's quadrants is to use the maximum temperature and the rectangle, based on an initial ellipsis encompassing the whole muscle. The best shape to analyse the orbicular oris muscle is the rectangle with quadrants, based on an initial ellipsis encompassing the whole muscle.