An Electromyographic Analysis of the Temporalis Muscles and Certain Facial Muscles in Thumb- and Finger-sucking Patients

¹ Montreal, Canada, and Ann Arbor, Michigan

An electromyographic study of the temporalis muscles and some of the facial muscles was performed on 24 thumb- or finger-sucking children. A radiographic and cast analysis was included. Records of intraoral pressures developed by the subjects during sucking were also available. Twenty-one subjects showed remarkable consistency in their muscular behavior. The dominant muscle was either the orbicularis oris or the mentalis. The present findings in regard to swallowing were identical with Tulley's. There is some disagreement, however, with the observations of Rix and Gwynne-Evans. The muscular behavior was found not to be altered in the short period following sucking, but rather the abnormal patterns appeared to be firmly established and to persist.

The overbite values were the numerical values showing the greatest interest, without, however, being statistically significant. Overbite seems to be related to hyperactivity of the circumoral musculature. Abnormal behavior of the mentalis previously associated with Class II division I malocclusions was, in the present study, found on any skeletal or dental malocclusion.

This study has emphasized the thought that the seventh cranial nerve muscles form a physiological functional unit and cannot easily be isolated electromyographically. It finally reflects the theory that malocclusion caused by thumb-sucking is more a matter of individual response to stimuli than a highly classified cause-and-effect syndrome.