A "tongue thrust" swallowing pattern is considered a myofunctional disorder, and can cause problems with dental development, speech, facial muscle tone, and even breathing.
It is a behavioral pattern in which the tongue protrudes through the teeth during swallowing, speech, and rest. This bad habit often begins with frequent thumb-sucking or use of a pacifier as an infant. The brain is conditioned to thrust the tongue forward even after the sucking habit is no longer present.
Tongue thrust often coincides with poor resting tongue posture (low in the mouth rather than along the palate) and can result in an open bite and pushing the teeth and facial bones forward.
With healthy function, the tongue should be placed on the roof of the mouth rather than between the teeth during a normal, healthy swallow.
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Video from YouTube Channel: TMJOrthoCentre https://youtu.be/BlskRpsj3u8