A normally relaxed or rest position of the mouth includes having the lips closed, teeth slightly apart, and the tongue resting behind the upper front teeth and up on the palate tissue just behind the upper teeth.
When a person swallows incorrectly, the tip and/or the sides of the tongue press against and spread between the teeth. The tongue becomes prominent or visible when talking, swallowing, or eating, and can create eating, speech and cosmetic problems. This is referred to as a tongue thrust.
A tongue thrust and a low, forward rest position of the tongue tip often occur together. When a tongue thrust is observed with a malocclusion, it’s commonly presumed that the tongue thrust caused the teeth to become out of alignment. But where the tongue tip resides at rest is also an important factor. An abnormal tongue rest position can result in dental changes over time. In the same way that a slight and continuous force is what orthodontists and dentists use to move teeth, continuous and prolonged thrusting and sucking habits can also cause a change in the shape of the palate, the dental arches, and the position of teeth.
Positioning the teeth into correct position, but without correcting disfunctional habits of the orofacial muscles and rest position of the tongue, is likely to result in relapse and recurrence of malocclusion.
When the tongue rests in a normal position and functions normally during eating, swallowing and speaking, the teeth can then be placed in a normal position and should remain stable, without future relapse.