The association of malocclusions with masseter muscle thickness based on ultrasonography measurements: a retrospective cohort study.

Aim
To investigate whether the functional capacity of elevator masticatory muscles, estimated by masseter muscle thickness, is associated with malocclusions in the sagittal, vertical, and transverse axes.
Materials And Methods
670 consecutive cases were evaluated. Pre-treatment dental casts were examined for malocclusion characteristics (overjet, sagittal molar relationships, overbite, posterior crossbite), and ultrasonographic measurements of the masseter muscles were used for thickness measurements. Gender, age, and BMI were also recorded. A multiple linear regression analysis was conducted to investigate the association of masseter thickness with age, gender, BMI, and malocclusions. A subgroup analysis across age groups explored whether age and gender had a different impact on their association with masseter muscle thickness, and a paired t-test examined possible asymmetry in masseter muscle thickness between the crossbite and non-crossbite sides.
Results
Males showed thicker masseter muscles than females by 0.8 mm. Older-growing individuals presented thicker muscles, with a 1-year age increase resulting in a 0.1 mm increase in mean thickness, and patients with increased values of BMI presented thicker muscles. A 1mm overbite increase was associated with 0.1mm thicker masseter muscle. Patients with unilateral posterior crossbite showed thinner muscles on their crossbite (11.15 mm) than the non-crossbite side (11.42 mm) with a mean difference of 0.27 mm (P = 0.002).
Conclusions
Masseter muscle thickness was greater in males, subjects with increased values of BMI, and older-growing individuals, showing age-related growth that plateaued in adulthood. Patients with deep bite had thicker muscles, while patients with unilateral posterior crossbite showed thinner muscles on their crossbite side than on the non-crossbite side.