Background: Masseter muscle thickness and its relationship with vertical craniofacial morphology have been extensively studied in adults, but data on children are lacking.

Objective: To examine the association between masseter muscle thickness and vertical cephalometric parameters in a group of Class II malocclusion growing children.

Methods: The current study design was retrospective and cross-sectional, looking at a sample of 211 growing children with Class II malocclusion between the ages of 6 and 15 derived from two centers. Ultrasonographic masseter muscle thickness measurements and vertical cephalometric variables, including the gonial angle, were evaluated before any orthodontic treatment had been carried out. Multiple linear regression analysis was used to examine the association between masseter muscle thickness and vertical cephalometric measurements, including age and patient origin as independent variables in the analysis.

Results: In the present sample, masseter muscle thickness was found to be independent of sex, but correlated with age, with older children presenting thicker masseter muscles. In the total patient sample, using multiple regression analyses, children with thicker masseter muscles had significantly smaller intermaxillary and gonial angles. No other cephalometric vertical characteristics showed associations with masseter muscle thickness.

Conclusion: In growing children with Class II malocclusion, those with thicker masseter muscles are more likely to display smaller intermaxillary and gonial angles respectively.