Predictive value of masseter muscle thickness and bite force on Class II functional appliance treatment: a prospective controlled study.

AIM To prospectively evaluate the functional capacity of the masticatory musculature as a predictive variable in determining functional appliance treatment outcomes in Class II/1 malocclusion children. METHODS Twenty Class II/1 malocclusion children (11.4 ± 1.7 years) were treated with functional appliances during 1 year. Masseter muscle thickness and maximal molar bite force measurements, lateral cephalograms, and study casts were taken before and after treatment. Twenty age- and gender-matched untreated children were included as a control group. Regression analyses were used to identify correlations between pre-treatment muscle characteristics and treatment outcomes. RESULTS All treated patients showed dentoalveolar sagittal improvement. Maximal molar bite force and masseter muscle thickness decreased during the treatment period in the experimental group but increased in the control group. Children with lower pre-treatment maximal molar bite force showed more mesial movement of mandibular first molars, distal movement of maxillary first molars, and larger change in molar class during treatment. Children with thinner pre-treatment masseter muscles demonstrated more mandibular first molar mesialisation, mandibular incisor proclination, and opening of the gonial angle during treatment. CONCLUSIONS The initial condition of the masticatory muscles may partly determine treatment outcomes. Children with thinner pre-treatment masseter muscles or weaker bite force show greater dentoalveolar changes.