An underbite is a common jaw misalignment where the lower front teeth and jaw protrude past the upper front teeth when the mouth is closed. This condition reverses the normal bite relationship. While sometimes linked to hereditary factors, the underlying problem often involves bone structure, making the timing of treatment a primary concern for parents. The American Association of Orthodontists recommends that children receive their first orthodontic screening no later than age seven, which allows for early identification of this and other developing bite problems.
Defining the Skeletal Underbite
The term “underbite” encompasses two distinct categories: dental and skeletal issues. A dental underbite is less complex, occurring when the teeth are misaligned despite the jawbones being correctly positioned. This condition typically responds well to traditional orthodontic methods that focus on moving the teeth into proper alignment.
A skeletal underbite involves a growth discrepancy in the jawbones themselves. This often presents as mandibular prognathism, where the lower jaw (mandible) has grown excessively forward, or a retrognathic maxilla, where the upper jaw has not developed enough. Skeletal discrepancies are far more challenging to correct because they involve the structure of the facial bones. Correcting a skeletal underbite is highly time-sensitive, as intervention must occur before the body finishes its adolescent growth phase.
The Critical Window for Correction (Ages 6 to 10)
The most favorable time to correct a skeletal underbite is during a child’s early growth years, between the ages of six and ten. This period is referred to as Phase I treatment, where the goal is to modify the direction of jaw growth. Orthopedic correction is possible because the sutures connecting the facial bones are still pliable and responsive to external forces.
The primary objective of this early intervention is to restrain the forward growth of the lower jaw while simultaneously encouraging the forward development of the upper jaw. A common appliance used to achieve this is the reverse-pull headgear, often called a face mask, which applies gentle, consistent force. This device typically works in tandem with a palatal expander, which widens the upper jaw to facilitate its forward movement.
The mechanical action of the reverse-pull headgear applies tension to the upper jaw, resulting in its forward and downward displacement. This movement also encourages a slight backward and downward rotation of the lower jaw. Successfully guiding this growth often prevents the need for more invasive procedures later in life. Early treatment improves the chance of correcting the jaw discrepancy non-surgically, setting the foundation for the permanent teeth to erupt into a better alignment.
Treatment Options for Older Patients
When the window for growth modification treatment is missed, treatment for adolescents and adults becomes more complex. For patients who are still growing but past the peak window for orthopedic correction, or for adults with mild to moderate skeletal issues, orthodontic camouflage may be an option. This approach involves using braces to reposition the teeth to mask the underlying skeletal problem.
Camouflage treatment works by moving the upper front teeth slightly forward (proclining the maxillary incisors) and the lower front teeth slightly backward (retroclining the mandibular incisors). The goal is to create a functional bite where the teeth meet correctly, even though the jawbones remain misaligned. This method is generally only suitable when the facial profile is already acceptable, and the skeletal issue is not pronounced.
For severe skeletal underbites in patients whose growth is complete, orthognathic surgery is the solution. Growth is typically considered complete for surgical planning around age 15 to 18 for females and 17 to 21 for males. Jaw surgery involves an oral and maxillofacial surgeon physically repositioning the lower jaw backward or the upper jaw forward. This comprehensive treatment usually requires a period of orthodontic preparation with braces both before and after the surgical procedure to ensure the teeth align perfectly in the newly corrected jaw position.
Long-Term Impact of Untreated Underbites
Ignoring a skeletal underbite can lead to functional and health complications. The misalignment causes the teeth to meet improperly, leading to uneven wear on the front teeth. This premature wear can cause chipping and increase the long-term risk of tooth fracture and sensitivity.
An uncorrected jaw discrepancy can also compromise the ability to chew food efficiently. Furthermore, the incorrect resting position of the jaw can place undue stress on the temporomandibular joints (TMJ), potentially resulting in chronic jaw pain, headaches, and limited jaw movement. Untreated underbites can also affect speech clarity, making the pronunciation of certain sounds difficult.