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.

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Nasal breathing is a physiologically normal form of breathing in human. When this normal breathing is disordered by nasal obstruction, various symptoms such as headache, fatigue, sleep disorder, daytime sleepiness, and decline in diligence and QOL may occur. The nose is the portal of the respiratory system, and carries out olfaction and air conditioning, such as heating, humidification, and purification of inhaled air. Nasal airway resistance controls respiratory rhythm and depth. Nasal obstruction is a common upper respiratory symptom, and is caused by various kinds of diseases. A diagnosis of nasal obstruction is made by anterior rhinoscopic findings, endoscopic findings, rhinomanometry, acoustic cross-section measurement, and imaging. Treatment of nasal obstruction depends on the causative disease. Medical treatment is selected for reversible nasal obstruction, whereas surgical treatment is indicated for drug-resistant and irreversible nasal obstruction. Recent advances in endoscopes and other such instruments have enabled us to perform most of the sinonasal surgeries via an endonasal endoscopic approach. Several epidemiological and clinical studies have revealed that nasal obstruction is one of the major causative factors of sleep-disordered breathing. Several different mechanisms are considered to explain why nasal obstruction induces sleep-disordered breathing :1 ) An increase of nasal airway resistance induces a negative pressure of the pharynx and then narrows the pharyngeal space. 2) Nasal obstruction induces mouth breathing, and the mandible and hyoid bone shift backward. As a resul t, the base of the tongue sinks and the pharyngeal space collapses. 3) A decrease of nasal air flow suppresses input signals to a nasaVnasopharyngeal air flow perception receptor, which causes the relaxation of pharyngeal dilator muscles such as the geniohyoid muscle, and then the pharyngeal space collapses. 4) A decrease of input signals to the air flow perception receptor directly suppresses the respiratory center. In infants, the soft palate and epiglottis are located close to each other. Because of this anatomical characteristic, nasal obstruction readily induces infantile sleep-disordered breathing. Mouth breathing in the growth period impairs maxilo-mandibulo-facial growth, which can be an additional permanent risk factor for sleep-disordered breathing as the patient grows. Early therapeutic intervention in pediatric patients with nasal obstruction is, accordingly, important to prevent such an unfavorable outcome.

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When patients complain that they open the mouth at rest on many occasions, dentists are likely to conclude that they are mouth breathers. Such mouth breathing might relate especially to tongue habits affecting antero-posterior and horizontal balances of the force on the occlusion. In­ competent lip is one of the functional disorders in maxillary protrusion, and improving the functional disorder will lead to significant improvement in the aesthetic problem. In addition, vertical problems of the dento-facial complex will also affect the lip sealing function. Maxillary protrusion is characterized by features such as labial inclinations of the upper incisor or a retruded position of the mandible. However, maxillary protrusion might exhibit not only a problem at the anterior-posterior position of the dentition but also a vertical problem of a maxillofacial area and occlusion. To improve malocclusion with vertical discrepancies, we are able to choose options such as the extrusion of incisors, intrusion of the molars using headgear and implant anchor and surgical impaction of the maxilla. The last two will result in the upward rota­tion of the mandible. I presented the diagnosis, treatment method, and prognosis of the following cases, which had a vertical problem with functional disorder of the tongue and incompetent lip. 1) Improved the lip sealing function by mechanical orthodontic treatment 2) Improved the open bite with correction of the tongue habit 3) The treatment in the case with a higher facial height (a) Lingual movement of incisors (b) Depression of the molars using the implant anchor (c) Impaction of the maxilla with an orthognathic surgical treatment

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