Background: Anterior bite planes are bite-raising appliances used for deep bite correction. However, muscle responses to anterior bite planes of different harnesses may vary. Objectives:To prospectively evaluate masticatory muscle activity, muscle balance and maximum bite force (MBF) responses to anterior bite planes fabricated from acrylic resin (ABP) or bi-laminate thermoplastic (TBP) over 6 months in children with a deep bite.Methods: Sixty-six children were randomly assigned to the ABP, TBP or untreated control groups. Masticatory muscle activity, activity index (AC) and percentage overlapping coefficient (POC) were assessed by surface electromyography; MBF, using a custom-made bite force sensor. Data were collected before, immediately after appliance insertion and after 2 weeks and 1, 3 and 6 months of treatment. Within-and between-group differences were analysed using the one-way ANOVA/Kruskal-Wallis and Mann-Whitney U tests (α = .05); Friedman's tests were used to assess withingroup differences over time (α = .08).Results: At rest, no dependent variables changed throughout the study. At maximum clenching, masticatory muscle activity immediately dropped significantly but returned to baseline values and was equal to the control group at 1-3 months. The ABP group had significantly lower masseter activity and AC than the TBP group after insertion.Neither POC nor MBF were significantly different within or between groups. Conclusion:Masticatory muscle activity reduced after anterior bite plane insertion but returned to baseline after 1-3 months. Masseter activity decreased significantly more in the ABP group than TBP group. Neither appliance significantly affected POC or MBF.