The relationship between the upper and lower teeth, known as the bite or occlusion, is a significant determinant of oral health and function. A malocclusion refers to any misalignment of the teeth or an improper relationship between the upper and lower dental arches. An open bite is a distinct condition where the upper and lower teeth do not meet when the jaw is closed, leaving a visible gap. This gap can affect speech, chewing efficiency, and overall facial structure. The development of an open bite is complex, stemming from a combination of environmental habits, structural growth patterns, and inherited factors that influence the positioning of teeth and the growth of the jawbones.
Defining the Different Types of Open Bite
Open bites are classified based on where the lack of contact occurs, which helps identify the underlying cause. The most common type is the anterior open bite, characterized by a vertical space between the upper and lower front teeth when the back teeth are together. This condition can significantly impair the ability to incise food or correctly articulate certain speech sounds.
A less frequent variation is the posterior open bite, where the back teeth, typically molars or premolars, fail to make contact while the front teeth may meet normally. Open bites are also distinguished by their origin. A dental open bite is caused solely by the positioning or eruption of the teeth, often due to physical obstruction. Conversely, a skeletal open bite results from an underlying mismatch in the growth or size of the upper and lower jaws.
Habitual and Environmental Causes
The forces exerted by soft tissues, such as the tongue and lips, along with prolonged oral habits, are powerful enough to physically move teeth and alter alveolar bone growth, leading to dental open bites. A common factor is prolonged non-nutritive sucking, which includes thumb, finger, or pacifier use past the toddler years. The constant presence of the digit or appliance in the mouth prevents the normal vertical eruption of the front teeth and pushes them out of alignment.
This mechanical pressure directly interferes with the natural path of tooth eruption, creating a localized open bite in the area of contact. The duration and vigor of the habit are directly correlated with the severity of the malocclusion. If the habit continues past the age of three or four, the likelihood of self-correction diminishes significantly, often requiring orthodontic intervention.
Another contributing factor is an atypical tongue resting posture, often referred to as a tongue thrust. While a true “tongue thrust” during swallowing was once believed to be the primary cause, research indicates that it is the sustained, incorrect resting position of the tongue that applies sufficient force to move the teeth. The tongue should rest against the roof of the mouth; however, in individuals with an open bite, the tongue often rests low or presses between the upper and lower teeth. This constant, light pressure prevents the incisors from erupting fully, leading to the formation of the anterior open bite.
Chronic mouth breathing, often a result of airway obstructions like enlarged adenoids or chronic allergies, can further exacerbate this issue. When the mouth is habitually open to breathe, the tongue is forced to rest low in the floor of the mouth to maintain an open airway. This lower tongue position encourages a vertical growth pattern of the face and jaw. The disruption of the natural balance between the muscles of the tongue, cheeks, and lips allows the teeth to be pushed and held out of alignment.
Developmental and Structural Origins
Structural causes relate to the inherited framework of the face and jaws, often resulting in a skeletal open bite that is less influenced by environmental behaviors. A primary structural cause is a high-angle growth pattern, where the facial bones grow more vertically than horizontally. In these individuals, the lower jaw tends to rotate downward and backward, leading to a disproportionately long lower face height.
This vertical growth pattern increases the angle between the upper and lower jaws, making it physically impossible for the front teeth to overlap, even if the teeth themselves are positioned correctly. Genetic factors play a considerable role in determining the size and shape of the jawbones. These skeletal proportions predispose a person to a vertical growth trajectory that results in a skeletal open bite.
In adults, an open bite can occasionally develop or worsen due to degenerative conditions within the temporomandibular joint (TMJ). Conditions like TMJ osteoarthritis can cause the condyle, the ball of the jaw joint, to undergo progressive resorption. The loss of bone height in the condyle leads to a decrease in the vertical height of the lower jaw. This collapse of the joint component forces the mandible to rotate in a clockwise direction, effectively lowering the front of the jaw and creating an anterior open bite.
Intervention Timing and Preventive Measures
Because many open bites are caused by habits, the timing of intervention is directly related to the point at which the influence of the habit becomes permanent. For non-nutritive sucking habits, pediatric dentists recommend cessation by age three or four. When the habit is stopped before this window, the pressure on the developing teeth is removed, and the bite often has the potential to self-correct as the permanent teeth begin to erupt.
If the open bite persists due to a skeletal tendency or a persistent habit, early assessment allows for preventive measures to modify growth. The American Association of Orthodontists recommends that children have their first orthodontic evaluation no later than age seven. At this age, a mix of permanent and baby teeth is present, allowing the orthodontist to identify developing skeletal or functional issues.
Early Phase 1 treatment focuses on growth modification and habit correction, rather than comprehensive tooth alignment. This early intervention might involve the use of specialized appliances designed to discourage the tongue from resting between the teeth or to encourage a more favorable jaw growth trajectory. Addressing these underlying causes early can prevent the open bite from becoming more severe, potentially simplifying or reducing the need for more extensive orthodontic treatment later in adolescence.