Relationships between craniofacial morphology and masticatory muscle activity during isometric contraction at...

The aim was to investigate relationships amongst interocclusal distances, masticatory muscle electromyographic (EMG) activity during isometric contraction of masticatory muscles, and craniofacial morphology.

Twenty-eight women and 12 men (25.3 ± 3.8 years old) participated. After measuring maximal voluntary occlusal bite force (MVOBF) between the right-first premolars, the participants were asked to bite at submaximal levels of 0 (= holding the bite force transducer), 15, 22.5, and 30% MVOBF with the use of visual feedback. The thickness of a bite force transducer was set at 10, 12, 13, 14, 16, 17, 18, 19, 20, 22, and 24 mm (= interocclusal distance: IOD). Nine soft tissue craniofacial factors were assessed through digital photograph: face height, middle face height, lower face height, face width, inter-pupil distance and mandibular plane angle, lower face height / face height ratio, inter-pupil distance / facial width ratio and face width / face height ratio.

In the masseter muscle, EMG activity decreased with increased IODs. The participants with higher mandibular plane angle had more negative slope coefficients of IOD-EMG graphs at 0% MVOBF especially in male temporalis and female masseter and temporalis muscles, suggesting that a greater mandibular plane angle is associated with lower EMG activity at longer IOD.

Overall the findings support the notion that craniofacial morphology is associated with differences in neuromuscular activity of the masticatory muscles, and suggest that the neuromuscular effects of oral appliances may be dependent on patients' craniofacial morphology and the thickness of the device. (247/250 words).