An underbite, medically known as Class III malocclusion, is a common orthodontic concern where the lower jaw protrudes beyond the upper jaw, causing the lower front teeth to overlap the upper front teeth. This misalignment affects the function of the entire bite and facial structure. For many individuals, particularly those with a skeletal discrepancy, the underbite does tend to worsen as they grow. This progression is largely dictated by the natural, differential growth patterns of the facial bones.
What Defines an Underbite
An underbite is characterized by a “reverse overjet,” where the lower incisors sit in front of the upper incisors when the jaw is closed. This condition can range from mild, involving only a few teeth, to severe, where the entire lower jaw is noticeably forward, creating a concave facial profile. Underbites are classified into two primary types based on their origin.
A dental underbite is primarily an issue of tooth positioning, meaning the teeth are angled incorrectly despite the upper and lower jaws being relatively well-aligned. Conversely, a skeletal underbite, often called mandibular prognathism, is caused by a discrepancy in the size or position of the jaw bones. This skeletal type is generally considered more severe and has a greater tendency to worsen. Skeletal underbites are strongly linked to genetics, which dictates the size and shape of the maxilla (upper jaw) and the mandible (lower jaw).
Growth and Skeletal Progression
The primary reason an underbite can worsen is the difference in growth patterns between the upper and lower jaws during development. The maxilla (upper jaw) typically completes its significant forward growth earlier, generally around the onset of puberty. In contrast, the mandible (lower jaw) often experiences a later and more prolonged growth spurt, sometimes continuing to grow aggressively well into the late teens or early twenties, especially in males.
For a child predisposed to a skeletal underbite, this differential growth can significantly compound the misalignment. As the mandible continues its forward growth after the maxilla has slowed, the lower jaw effectively outgrows the upper jaw, thereby increasing the severity of the underbite. The mandible can grow in length at nearly twice the rate of the maxilla during this period.
Once an individual reaches full skeletal maturity, typically in late adolescence or early adulthood, the major growth-related worsening of the underbite ceases. This completion of facial growth is a defining factor in determining the final treatment strategy, as growth modification is no longer an option.
Impacts of Untreated Underbites
Allowing an underbite to persist without correction can lead to a variety of functional and health issues. The misalignment of the jaws results in inefficient chewing and causes uneven and excessive wear on specific teeth, often leading to chipping or premature erosion of the enamel.
The strain placed on the jaw joint by the misalignment can contribute to issues with the temporomandibular joint (TMJ), potentially causing chronic jaw pain, clicking, or difficulty opening and closing the mouth. Furthermore, a significant underbite can affect speech clarity, sometimes resulting in a lisp or other impediments. The noticeable change in facial profile associated with a severe underbite can also have a considerable psychological impact.
Intervention Strategies
The approach to correcting an underbite is highly dependent on the patient’s age and their stage of skeletal growth. Early intervention, or interceptive treatment, is typically recommended for children around ages seven to ten, while the jaw bones are still malleable. These early treatments, such as palatal expanders or reverse-pull face masks, are designed to guide and stimulate the forward growth of the maxilla while restricting the growth of the mandible.
For adolescents and teens, traditional braces or clear aligners are used to correct the dental component and align the teeth within the existing jaw structure. Once skeletal maturity is reached, typically in the late teens, severe skeletal underbites can no longer be corrected by growth modification alone. At this point, the definitive solution often requires a combination of orthodontics and orthognathic surgery (jaw surgery) to physically reposition the maxilla and/or mandible to achieve a stable and functional bite.