Open mouth posture may indicate incompetent lip closure and refers to the chronic lack of a lip seal when at rest. Individuals that have a habitual open mouth posture may have to strain the muscles to keep the lips sealed.18 Other clinical signs may present with the open mouth posture, including a larger lower lip, untoned oral muscles, inflammation of the anterior gingiva, and/or increased plaque buildup on the anterior teeth surfaces (Figure 7).
Figure 7. Clinical appearance of chronic open mouth posture.
Courtesy of: Dr. Péter Vályi
Some individuals with open mouth posture may have an additional habit of breathing through the mouth instead of the nose. Categories of mouth breathing include: habitual, seen when a correct nasal breathing behavior was never established; obstructive, as seen with chronic allergies or enlarged tonsils; or anatomic, seen if the individual is simply unable to take in enough air through the nose.19 With a mouth breathing behavior, the individual does not receive the benefits of the nasal cavity’s particulate filtering design. Orofacial consequences of open mouth posture and/or mouth breathing may include increased risk for caries, gingivitis, speech problems, and dental malocclusion.18,20 If left untreated throughout puberty, a mouth breathing habit is believed to contribute to abnormal facial development (Figure 8).21,22
Figure 8. Change in facial development due to allergies and obstructive mouth breathing.