Abstract

This study was initiated to compare electromyographically the activity of the masseter and temporal muscles during the early retentional period in orthodontic patients. Electromyographic recordings were taken at the following times: (1) before typical edgewise appliance was removed, (2) at time of retainer insertion, (3) after eight to twelve weeks of retainer wearing, and (4) one day following occlusal equilibration. Electromyograms from the orthodontic group of subjects were compared with electromyograms from a group of subjects with normal occlusion, and a group of subjects with untreated Class II, Division 1 malocclusions. There was a total of thirteen subjects studied: five orthodontic subjects, five normal subjects, and three Class II, Division 1 subjects.

Surface electrodes were attached to the skin over the middle fibers of the temporal muscle and over the masseter muscle near the gonial angle of the mandible. The bio-electric activity in the four muscle units was recorded with a Grass polygraph, Model 5A. The electromyographic symbols were recorded simultaneously by a four-channel magnetic ink writer.

The subjects performed various exercises. The gum chewing and deglutition exercises were the most significant, in that they demonstrated normal physiologic function. The electromyographic records were carefully examined for gross aberrations. The general characteristics of the electromyograms of the three groups can be summarized as follows:

  1. The orthodontically treated subjects after equilibration and the normal occlusion subjects displayed an electromyographic record that denoted syngergy[sic] and coordination in the bilateral contraction patterns of the temporal and masseter muscles.

  2. The orthodontically treated subjects before, and shortly after, edgewise appliance was removed and also the Class II, Division 1 malocclusions displayed bilateral contraction patterns of the temporal and masseter muscles that were asynchronous and uncoordinated with erratic periods of relaxation.

  3. It was found that during masticatory function on the ipsilateral (working) side, orthodontically treated subjects, after occlusal equilibration, and normal subjects showed more masseter than temporal muscle activity. The situation was reversed in the orthodontically treated subjects before, and shortly after edgewise appliance was removed, and also in the Class II, Division 1 group.

  4. The orthodontically treated subjects after equilibration, and the normal occlusion subjects showed that the masseter muscle activity was predominant over the temporal muscle activity during deglutition. Activity of the temporal muscle was predominant in the Class II, Division 1 subjects during deglutition.

Observations in this study substantiate the claim that the masseter muscle is designed to function as a power muscle and that the temporal muscle functions as a postural muscle. Excellence of muscle function is one of the goals of orthodontics; therefore, orderly and selective occlusal equilibration should be included in a complete orthodontic retention plan. The muscle function of the orthodontic group of this study was improved by equilibration.

LLU Discipline

Orthodontics

Department

Dentistry

School

Graduate School

First Advisor

Thomas J. Zwemer

Second Advisor

Howard W. Conley

Third Advisor

Roger Helmandach

Fourth Advisor

Walter H. B. Roberts

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

1964

Date (Title Page)

6-1964

Language

English

Library of Congress/MESH Subject Headings

Masticatory Muscles

Type

Thesis

Page Count

vii; 65

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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