Soft Tissue Facial Planes and Masticatory Muscle Function in Skeletal Class III Patients Before and After Orthognathic Surgery Treatment

Purpose

To noninvasively assess the facial soft tissues and masticatory muscle function before and after orthognathic surgery.

Patients and Methods

Eight patients aged 18 to 36 years, all with a skeletal Class III and mandibular asymmetry, were assessed both before (on average, 2 months) and after (on average, 10.5 months) surgical intervention (mandibular reduction by sagittal split osteotomy and Le Fort I maxillary advancement). From the 3-dimensional coordinates of soft tissue facial landmarks, the inclination of facial planes was calculated. Surface electromyography of the masticatory muscles was performed and indices of muscular activity computed. Data were compared with reference values collected in healthy subjects of the same gender, age, and ethnic group.

Results

Before surgery, facial planes were significantly less horizontal (frontal plane) than in the reference subjects (P < .05). The sagittal projection of the mandibular plane was more inclined relative to the norm (P < .001). During teeth clenching, all indices of standardized muscular symmetry, torque, and activity (P < .05) were smaller than the reference values. After surgical treatment, the inclinations of facial planes became more homogenous (P < .05). The inclination of the frontal and sagittal planes came next to the reference values, but still differed significantly in the patients (P < .05). The mean symmetry index of masseter muscle, torque coefficient, and pooled muscle activity increased, but the patient values remained significantly under the reference values (P < .05).

Conclusion

The morphologic and functional approach used in this study proved useful as a complementary diagnostic aid, enabling quantitative evaluation of the final results of surgery, without submitting the patients to invasive procedures.