Masticatory Muscle Characteristics as a Biological Explanation for Interindividual Variability During Class II Functional Appliance Treatment: A Conceptual Synthesis

To conceptually synthesize existing evidence on whether masticatory muscle characteristics, assessed by masseter muscle thickness, may explain interindividual variability in skeletal and dentoalveolar treatment outcomes following functional appliance therapy in children with Class II malocclusion. Additionally, to explore the potential of the mandibular gonial angle as a practical cephalometric indicator for predicting treatment response.

Previously published studies investigating the effects of functional appliances on skeletal and dentoalveolar outcomes in children with Class II malocclusion were conceptually synthesized. Particular attention was given to the relationship between baseline masseter muscle thickness, mandibular gonial angle, and treatment-related skeletal and dentoalveolar adaptations.

The available evidence suggests that baseline masticatory muscle characteristics may influence treatment outcomes. Children with reduced masseter muscle thickness tend to exhibit greater dentoalveolar adaptations, including increased mandibular incisor proclination and distal displacement of the maxillary dentition. As the gonial region represents the attachment site of the masseter and medial pterygoid muscles, variations in muscle size and functional loading may influence gonial morphology. A more obtuse gonial angle appears to be associated with greater dentoalveolar compensation during functional appliance therapy, characterized by increased mandibular incisor proclination and maxillary incisor retroclination.

Masticatory muscle characteristics may contribute to interindividual variability in treatment response to functional appliances in children with Class II malocclusion. The mandibular gonial angle may serve as a practical surrogate cephalometric marker for identifying patients who are more likely to exhibit predominantly dentoalveolar rather than skeletal adaptations. However, further clinical studies are required to validate its predictive value and clarify the relationship between masticatory muscle characteristics and treatment outcomes.