Craniofacial morphology and its association with masseter and medial pterygoid muscle thickness

Background: Craniofacial development and masticatory muscle growth are intricately linked, influenced by both genetic and functional factors. Whereas previous studies have investigated these associations using traditional morphometric methods, geometric morphometric tools provide an innovative approach to analyzing craniofacial variation and masticatory muscles. Aims: This study aimed to investigate the association between craniofacial morphology and the cross-sectional areas (CSA) of the masseter and medial pterygoid muscles using Procrustes-based geometric morphometrics on magnetic resonance imaging (MRI) data from a population-based sample in eastern Germany. Methods: Data were obtained from 692 participants in the Study of Health in Pomerania (SHIP). Craniofacial landmarks were identified on MRI scans, and muscle CSAs were measured using image segmentation techniques. Principal component (PC) analysis was used to assess morphological variation. Regression models adjusted for sex, age, education, dental status, body height and weight, and centroid size were used to estimate associations between craniofacial shape and muscle CSA. Results: PC1, which primarily captured facial height and cranial base length, and PC2, which represented maxillary width and facial prominence, were associated with medial pterygoid muscle CSA. Longer faces (PC1) were associated with thinner pterygoid muscles, while wider midfaces (PC2) were associated with larger CSA. The association between the masseter muscle and craniofacial morphology was unclear. However, the masseter muscle was strongly associated with dental status and sex. Conclusion: Craniofacial variation, particularly in terms of facial height and midface width, was associated with the medial pterygoid muscle. In contrast, masseter muscle size was associated with factors other than shape to a very large extent. These findings highlight the distinct anatomical and functional roles of masticatory muscles.