Tongue thrusting, also known as an orofacial myofunctional disorder (OMD) or reverse swallow, describes a pattern where the tongue pushes forward against or between the teeth during swallowing, speaking, or at rest. This action involves an imbalance in the muscles of the tongue, lips, and face, altering the typical mechanics of the mouth. A mature swallow requires the tongue to press against the hard palate, or roof of the mouth, to propel food or liquid down the throat. When the tongue instead pushes forward, it exerts pressure against the dentition. While this pattern is normal for infants, its persistence into adulthood can lead to dental, speech, and respiratory issues.
Retained Childhood Habits
Adult tongue thrusting is often rooted in the persistence of immature muscle patterns developed early in life. The infantile swallow, which involves the tongue protruding forward, is necessary for nursing but should naturally evolve into a mature swallow by approximately age seven or eight. When this transition is delayed or incomplete, the learned behavior becomes an ingrained habit in the adult motor system.
Prolonged non-nutritive sucking habits are a major factor that trains the tongue to function incorrectly. Habits such as thumb, finger, or pacifier sucking past the recommended age physically force the tongue into a low, forward position. Extended use of bottles or sippy cups that require a sucking motion instead of a mature swallowing pattern can also reinforce this dysfunction.
These early oral habits condition the muscles to adopt an incorrect resting posture and movement. Even after the physical object is removed, the established nerve pathways continue to execute the reverse swallow pattern. This learned muscle action becomes an involuntary, subconscious movement, making correction difficult without targeted intervention.
Structural and Dental Factors
The physical structure of the mouth and jaw complex can either predispose an adult to tongue thrusting or be a consequence of the habit itself. Malocclusion, or the misalignment of the teeth, is closely linked to the condition, particularly an open bite. An anterior open bite occurs when the upper and lower front teeth do not meet, creating a space the tongue instinctively tries to fill during swallowing or rest.
Jaw misalignment, such as an underbite or overbite, can also alter the functional space available for the tongue. This misalignment disrupts the natural equilibrium between the forces exerted by the tongue, cheeks, and lips. The tongue’s constant pressure against the teeth, rather than the palate, can gradually push them out of alignment.
Physical Obstructions
In some cases, an abnormally large tongue, known as macroglossia, physically occupies too much space within the oral cavity. This structural issue forces the tongue into a forward-facing position, resting against or between the teeth. Similarly, a restricted lingual frenulum, or tongue-tie, prevents the tongue from elevating fully to the palate, resulting in a low resting posture that encourages a forward thrust during function.
Airway and Respiratory Influences
Respiratory factors represent one of the most common causes of tongue thrusting in adults, as they force a functional adaptation of the tongue’s posture. The tongue’s position is intrinsically linked to maintaining a clear airway, and chronic obstruction to nasal breathing prompts the body to compensate. When nasal breathing is difficult, the individual switches to chronic mouth breathing to ensure adequate oxygen intake.
Persistent nasal obstruction, often due to conditions like chronic allergies, a deviated septum, or the presence of enlarged tonsils or adenoids, necessitates this open-mouth posture. To facilitate the flow of air through the mouth, the jaw drops slightly, and the tongue must move down and forward, away from the palate. This low resting posture is a survival mechanism to keep the oral airway open.
Once the tongue is positioned low and forward, it cannot execute the mature swallowing pattern, which requires a firm seal against the hard palate. Instead, the tongue must push forward against the teeth or between them to create a seal necessary to propel the food bolus down the throat. This forward push, or thrust, is an acquired secondary habit that accommodates the primary issue of an obstructed airway and low resting tongue posture. This chronic adaptation, driven by the need to breathe, sustains the tongue thrusting pattern in adulthood.