Abstract
Since Angle class II division 1 malocclusion associated with mouth breathing has been demon- strated. mouth breathing has been said to be a cause of maxillary protrusion. However. association with maxillary protrusion has not been mentioned in recent clinical and animal experiment studies. Questionaire surveys about breathing have been carried out for understanding the cause of the malocclusion in the dental clinic. However, the questionaire surveys did not necessarily af-firm habitual mouth breathing, because opening the lips in those with incompetent lip is some times mistaken for a symptom of mouth breathing. Therefore. it is necessary to evaluate the breathing mode objectively for examining the etiological relationship. We objectively evaluated breathing modes using CO2 sensors. and divided subjects into nasal. complete and partial mouth breathing groups. It was found that questionnaires on mouth breathing do not provide accurate answers about the route of breathing, and nasal resistance is not a decisive factor for mouth breathing.
On the other hand. it has been said that eruptive and occlusal forces determine the vertical position of molars. and the degree and duration of force are other factors determining tooth position. If the vertical effect of the occlusal force on the posterior teeth is decreased, the posterior teeth will extrude and the mandibular shows a downward rotation. resulting open bite. In mouth breathing, the oral cavity will bear two duties. mastication and respiration. However. the two functions will not be performed at the same time. We found that chewing activity was impeded and reduced during mouth breathing because breathing is the most important function for maintaining life. The impeded and reduced chewing activity will induce extrusion of the posterior teeth and a downward rotation, resulting the open bite. Thus, we identified the mechanism by which habitual mouth breathing affects the vertical growth of the face.
The intruding the posterior teeth and upward impaction of the maxilla are important ways to correct the vertical discrepancies of the face. We have searched out other strategies to preserve the vertical position of the posterior teeth after active orthodontic or orthoganthic surgical treatment. We investigated the effect of isometric clenching by voluntary contraction against a soft bite block on various occlusal parameters. It was found that such isometric muscle exercise has benefit in intruding the posterior teeth and upwardly rotating the mandible. These are mecha nisms for improving anterior open bite using alternative treatment methods.
In addition, in a survey using the questionnaire on chewing gum habits, we found that many people have the habit of chewing gum, with the most popular reasons being refreshment, enhanced concentration, and stress release. It was found that gum chewing exercise program is also usable for increasing occlusal contact area as well as the isometric clenching exercise, and it is also comfortable enough and less stress to continue the chewing gum exercise as a regular means.
