Ideally, at rest, the lips should be sealed without effort and the teeth slightly parted. The tongue should have the ability to rest at the roof of the mouth, rather than between the teeth. This posture represents balance between the facial musculature, lips, and tongue. Proper and effective feeding, chewing, and swallowing are secondary functions of this posture.
Chronic oral breathing is a common sign and/or symptom of oral motor disorder. This posture often involves altered sensation and impaired strength and coordination of the muscles of the mouth and face. This may be due to insufficient nasal airflow, tethered tissues (frenulum), and/or infrequent sucking and chewing, among other reasons.
A tongue thrust is the forward or sideways protrusion of the tongue into or between the teeth during swallowing; or at rest, when the tongue contacts more than half of the front and lateral teeth. Over time the light forces applied to the teeth by a resting tongue thrust are greater than intermittent pressures applied during swallowing. These forces have the ability to move teeth, especially in combination with open-mouth posture, as the lips no longer provide an inward counter force against the teeth.
Tongue-tie is a common term used to define limited tongue range of motion specifically due to the tethered soft tissue (frenulum) underneath the tongue. A tongue-tie can alter sucking, swallowing, speech, sleep, and facial growth. Increasing tongue range of motion with oral motor therapy is entirely possible, depending on the severity of the limitation. Additionally, oral motor therapy is often used prior to and following a tongue-tie release (frenectomy) to achieve full tongue mobility.