Does Unilateral Posterior Crossbite Affect Masticatory Muscles Activity?

Objectives: To test whether the electromyographic activity of masticatory muscles is asymmetric in children affected with unilateral posterior crossbite (UPCB), and to test the effects of orthopaedic maxillary expansion on muscular activity.
Methods: A cohort of 29 children (9.7±1.6 years) with UPCB (UPCB group) and 40 children (10.3±2.4 years) free of crossbite (Control group) were included. The electromyographic (EMG) activity of both left and right temporalis and masseter muscles was recorded during maximum voluntary clenching on cotton rolls, in intercuspal position and during unilateral 15 seconds chewing for both sides (T0). In the UPCB group the measurements were collected also immediately after (T1) and 3 months (T2) after UPCB correction.
Standardized indices for the assessment of muscular asymmetry (percentage overlapping coefficient, POC); potential lateral displacing components (unbalanced contractile activities of contralateral masseter and temporalis muscles, TC) and the electromyographic activity during maximum voluntary clenching on cotton rolls (COT) and in intercuspal position (CLENCH) for each muscle were calculated.
Baseline EMG data (T0) were compared between groups, moreover the effect of crossbite correction on EMG activity in UPCB group was assessed. Parametric and non-parametric tests for paired and unpaired data were performed.

Results: At T0, UPCB group showed an asymmetric muscular activity during clenching between cross VS. no cross side for both masseter (diff=-16.9±39.6 µV; P=0.029) and temporalis (diff=20.6±41,9 µV; P=0.013). These differences were not present in the control group. No significant differences were found between the two groups for all the other variables. After treatment, the UPCB group did not show any significant difference between the no cross/cross side for all the variables measured.
Conclusions: Children with UPCB have a slight asymmetric activity of the masticatory muscles. After treatment (T1 and T2), the UPCB group did not show any significant difference between the cross/no cross side.