Literature Reviews

–  Nakamura, Zerado and Yoshida  concluded that the masseter muscle’s activity level was significantly lower in the malocclusion group than in normal mice. It is, therefore, suggested that malocclusion interferes with optimizing the chewing pattern and establishing appropriate masticatory function.

–  It is also suggested that masseter muscle activity decreases following a reduction in masticatory stimulation of the periodontal ligament. Persistence of this condition might inhibit the growth and development of masticatory muscles and their function.

Angle Orthod. 2013;83:749–757

–  Rowlerson, Raoul & Daniel concluded that there were significant differences in percentage of occupancy of fiber types in masseter muscle in bite groups with different vertical dimensions.

–  Type I fiber occupancy increased in open bites, and conversely, type II fiber occupancy increased in deep-bites.

–  The association between sagittal jaw relationships and mean fiber area was less strong, but, in the Class III group, the average fiber area was significantly different between the openbite, normal bite, and deepbite subjects.

–  In the Class III subjects, type I and I/II hybrid fiber areas were greatly increased in subjects with deepbite.

Am J Orthod Dentofacial Orthop 2005;127:37–46

–  Keisuke, Yasuo and Kazuo employed electrophysiologic techniques (electromyogram) and found that masseter muscle activity decreases during the orthodontic treatment and this must be due to discomfort or pain and the alterations in the occlusal condition produced by the tooth movement or the ortho appliance itself.

The Angle Orthodontist – Vol 66 no3 1996, 223-228

–  Easton & David found that  there was an increase in action of lateral Pterigoid and Masseter muscles along with the slight increase in mandible in rats after treatment with a protrusive appliance


–  Carene & Steenberghe proposed that during the first phase of functional treatment ,reflexes in jaw muscles are transiently brought into imbalance. This phase of imbalance could act as a trigger for the mandible to attain a new functional position that subsequently leads to morphologic’ changes.

AM J ORTHOD DENTOFAC ORTHOP 90: 41 O-41 9, 1986.



  • The masticatory muscles include a vital part of the orofacial structure and are important both functionally and structurally.
  • The effect of muscle forces is three-dimensional although most orthodontists have considered it only one vector that is expansion.
  • A change in muscle function can initiate morphologic variation in normal configuration of the teeth and supporting bone, or it can enhance already existing malocclusion.
  • It is imperative that the orthodontist appraise muscle activity and that he conduct his ortho therapy in such a manner that the finished result reflect balance b/w structural changes obtain and the functional forces acting on the teeth an investing tissues at that time.


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  • Human anatomy by B.D. Chaurasia, 3rd ed.
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  • The Angle Orthodontist – Vol 66 no3 1996, 223-228
  • Virtual Journal of Orthodontics[serial online] 2011 September, 9 (2)
  • Am j orthod dentofac orthop 1990;97:149-58
  • Am j orthod dentofac orthop 90: 41 o-41 9, 1986.