Correlations between the cross‐sectional area of the jaw muscles and craniofacial size and shape

TLDR

Jaw muscle size experimentally reduces facial width and mandibular length in animals. The study measured cross‑sectional areas of adult human jaw muscles by CT and correlated them with facial angles and dimensions from lateral radiographs. Using 29 subjects, the authors quantified muscle areas and correlated them with six independent facial shape factors identified in a multivariate analysis of 50 subjects. The analysis found temporalis and masseter areas positively associated with facial width, while masseter and pterygoid areas correlated with mandibular length, supporting the hypothesis that jaw muscles influence facial growth and that each muscle has a distinct role.

Abstract

Abstract In adult human subjects, the correlations were determined between the cross‐sectional areas of the jaw muscles (measured in CT scans) and a number of facial angles and dimensions (measured from lateral radiographs). Multivariate statistical analysis of the skeletal variables in a group of 50 subjects led to the recognition of six independent factors determining facial shape, i.e, 1) cranial base length, 2) lower facial height, 3) cranial base flexure and prognathism, 4) facial width, 5) mandibular length, and 6) upper facial height. In 29 of these subjects, the cross‐sectional areas of the jaw muscles were determined, and correlations between these areas and the scores on the above‐mentioned factors were calculated. It appeared that the cross‐sectional areas of temporalis and masseter muscles correlated positively with facial width, whereas the areas of masseter and both pterygoid muscles did so with mandibular length. It has been shown experimentally that a decrease in jaw muscle size in various animals likewise has an effect on facial width and mandibular length. Our results therefore support the hypothesis that in man too the jaw muscles affect facial growth and partly determine the final facial dimensions. They also hint that the role of each muscle is different.