An open bite (malocclusion) occurs when the upper and lower teeth fail to make vertical contact when the back teeth are closed. This condition is most often observed as an anterior open bite, leaving a visible gap between the top and bottom incisors. Instead of the upper front teeth slightly overlapping the lower ones, the teeth slant outward and apart. An open bite affects a person’s ability to chew, speak, and maintain proper jaw function.
Acquired Habits and External Pressures
Persistent learned behaviors, particularly in childhood, apply continuous external pressure to the developing dental arches. Prolonged non-nutritive sucking habits, such as thumb or finger sucking, physically prevent the proper vertical eruption of the incisor teeth. The constant presence of the digit acts as a physical barrier, guiding the teeth into an open position.
The severity of the open bite relates directly to the duration, frequency, and intensity of the sucking habit. Dental professionals recommend intervention if the habit persists past age three or four, as permanent dental changes become more likely after this age. Extended pacifier use, especially beyond age three, is also strongly linked to a higher incidence of anterior open bite.
The force exerted by these habits also influences the underlying jaw structure. Pressure from the thumb or pacifier can cause the palate to become higher and narrower. This structural change affects how the upper and lower teeth fit together, sometimes leading to a posterior crossbite in addition to the open bite. When these habits are stopped early, the body often has the potential for natural correction of the dental alignment.
Skeletal and Genetic Influences
While habits cause a dental open bite by moving the teeth, a skeletal open bite results from an underlying structural issue with the jawbones. This malocclusion relates to the inherent growth pattern of the facial skeleton, which is largely dictated by genetics. The issue involves the disproportionate size or angle of the maxilla (upper jaw) and mandible (lower jaw), not merely the position of the teeth.
A common manifestation of this skeletal pattern is “long face syndrome,” characterized by excessive vertical facial development. This growth pattern involves the back portion of the jaw growing more than the front, causing the mandible to rotate downward and backward. This rotation increases the lower facial height and prevents the front teeth from achieving vertical contact.
The vertical proportions of the face are highly controlled by genetic factors. An individual may inherit a hyperdivergent growth pattern, meaning the jawbones tend to grow away from each other vertically, predisposing them to an open bite. This distinction is significant because a skeletal open bite occurs irrespective of oral habits and involves the bone structure.
Functional Factors: Tongue Posture and Airway
Muscle function and breathing patterns play a significant role in causing and maintaining an open bite. One primary factor is an atypical swallowing pattern, often called tongue thrusting or deviant deglutition. During a mature swallow, the tongue should press firmly against the palate, but in a tongue thrust, the tongue pushes forward between the front teeth.
The body swallows approximately 1,200 to 2,000 times every 24 hours, generating significant pressure with each swallow. This constant, repetitive force against the incisors prevents them from settling into a closed position, physically pushing them apart. The tongue’s resting posture can also apply this pressure against the teeth.
Airway issues, such as chronic nasal congestion or allergies, often compel a person to become a mouth breather. Mouth breathing is associated with a low resting tongue posture, where the tongue drops from the palate to facilitate air passage. The tongue normally acts as a natural orthopedic appliance, applying outward pressure that helps shape the maxilla. When the tongue is constantly positioned low, this supportive pressure is lost, contributing to a narrower upper arch and exacerbating the open bite.