Tongue thrust is perhaps the most widely identified OMD. Historically, tongue thrust was defined simply as the tongue exerting force against the anterior teeth during deglutition. Today, it is widely accepted that tongue behavior during swallowing is not the sole contributor to anterior open bites or myofunctional problems, but the position of the tongue at rest, such as a habitual forward or interdental tongue position, is also usually a contributing factor in anterior open bites.2,13 Therefore, tongue thrust now describes any behavior in which the anterior surface of the tongue makes repeated contact with any of the anterior teeth, or protrudes between the arches.14,15 A chronic tongue thrust behavior typically puts excessive pressure on the maxillary anterior teeth, and malocclusion in the form of an anterior open bite can occur (Figure 5).
In contrast, during normal deglutition and at rest, the anterior tip of the tongue should only come as far forward as to make contact at the retroincisal area of the palate, directly behind the maxillary anterior teeth. The body of the tongue should lift upwards into adequate palatal space and rest high near the palate. When the tongue rests towards the mandibular arch or the floor of the mouth, it is considered a low resting posture (Figure 6).