Evidence of muscle role over the cranio-facial skull development in Angle's Class III dental malocclusion under the clinical rest position.

Objective: The purpose of this study was to investigate correlations between masseter muscle activity and cephalometric measures in Angle's class III dental malocclusion under the clinical rest position.

Methods: Eight volunteers, both sex, age 7-12, were submitted to an electromyographic analysis of the masseter muscle, subdivided in the upper, medium and lower regions, and to a cephalometric analysis of 15 angle and linear measurements. After normalization, the data was subjected to a statistical, non-parametric Spearman correlation test, by means of the SPSS 12.0 program.

Results: Statistically significant correlations were observed between the clinical rest condition before and after the execution of exercises (a serie of mandibular movements), and the cephalometric measurements angle SN GoGn, angle SNA, angle SNB, angle SND, upper incisive. NA angle, upper incisive-NA distance, lower incisive. NB angle, lower incisive-NB distance and angle IMPA, and the different regions of the masseter muscle.

Conclusions: The significant statistical correlation found between the cephalometric analysis and the function of the masseter muscle indicate a strong influence of the musculature under a clinical rest condition over the cranial-facial development in the Angle's class III dental malocclusion. There is a selective activity of the different regions of the masseter muscle under the clinical rest condition in the Angle's class III dental malocclusion. There is a demand for research to complement these findings in other classes of dental malocclusion.