Malocclusion, often referred to as a “bad bite,” is the general term for misaligned teeth or jaws. When the upper and lower teeth do not meet correctly, it affects oral function and overall health. Among the most recognized types of this misalignment are the overbite and the underbite.
Defining and Differentiating Overbite and Underbite
An overbite, technically known as a deep bite or a Class II malocclusion, occurs when there is excessive vertical overlap of the front teeth. This means the upper front teeth cover too much of the lower front teeth when the jaw is closed. A healthy bite involves a vertical overlap of approximately 2 to 4 millimeters, where the upper teeth cover about one-third of the lower teeth.
When the upper teeth cover more than this ideal range, the condition is considered an excessive overbite or deep bite, sometimes causing the lower teeth to nearly disappear from view. This excessive overlap is distinct from overjet, which refers to the horizontal protrusion of the upper teeth beyond the lower teeth. A deep bite can be caused by a mismatch in jaw size, often where the lower jaw is smaller or shorter than the upper jaw.
Conversely, an underbite is a Class III malocclusion, characterized by the lower jaw extending too far forward relative to the upper jaw. This positioning causes the lower front teeth to overlap the upper front teeth, also described as a reversed overjet or an anterior crossbite. Underbites are often more noticeable because they can give the chin and lower jaw a prominent appearance. An underbite may range from a subtle edge-to-edge relationship between the front teeth to a severe protrusion of the lower jaw.
Factors Contributing to Jaw Misalignment
The primary reason for the development of malocclusions like overbites and underbites is genetic inheritance. Jaw shape and size are determined by genetics, meaning a person might inherit a smaller upper jaw from one parent and a larger lower jaw from the other, leading to a skeletal discrepancy. This inherited disproportion is a common underlying cause, particularly for underbites.
Prolonged habits during childhood are another factor that can influence jaw and dental alignment. Non-nutritive sucking behaviors, such as extended thumb sucking or pacifier use past the age of three, can exert pressure that pushes the upper teeth forward. This pressure can contribute to the development of an excessive overjet, which is associated with an overbite.
Tongue thrusting, where the tongue pushes against the front teeth during swallowing, can also affect tooth position over time. Dental issues play a role, including the early loss of baby teeth or the late loss of permanent teeth, which can disrupt the natural eruption path of other teeth. Missing teeth or the presence of extra teeth can cause the remaining teeth to shift out of proper alignment.
Health Implications and Treatment Options
Untreated overbites and underbites can lead to a variety of functional and health complications that extend beyond cosmetic concerns. Misalignment can result in difficulty properly chewing food, which may affect digestion and, in severe cases, contribute to nutritional issues. The improper relationship between the upper and lower teeth can also strain the jaw muscles and the temporomandibular joints (TMJ), potentially leading to chronic jaw pain and headaches.
The uneven bite forces resulting from malocclusion can cause abnormal wear on the tooth enamel, leading to premature chipping or fractures of the teeth. Crowded or severely overlapping teeth are also harder to clean effectively, which increases the risk for plaque buildup, tooth decay, and gum disease. In some instances, a deep overbite can cause the lower front teeth to bite directly into the gum tissue behind the upper front teeth, causing irritation and damage.
Orthodontic treatment aims to correct the bite relationship and align the teeth for better function and health. Treatment often involves fixed appliances like traditional braces or removable options such as clear aligners. These devices apply continuous, gentle force to gradually shift the teeth into their correct positions.
For more severe cases, especially those rooted in a significant skeletal discrepancy like a pronounced underbite, intervention may require a two-phase approach. This might include growth modification appliances in childhood to guide jaw development or, in adulthood, surgical intervention to physically reposition the jaws. Early diagnosis is recommended, as treating the condition while the jaw is still developing can yield better and less invasive results.