The question of whether a person can have both an overbite and an underbite simultaneously addresses a common confusion surrounding dental alignment, or occlusion. In the strict, scientific sense used by orthodontists, the answer is no, because these terms describe conditions that are mutually exclusive in the horizontal plane of the jaw. However, the perception of having both can arise from a combination of complex bite issues that affect the vertical, horizontal, and lateral relationships of the teeth. Understanding the precise terminology clarifies this apparent contradiction.
Understanding Dental Alignment Terminology
Dental misalignment, broadly termed malocclusion, is classified based on the three-dimensional relationship between the upper and lower teeth and jaws. The terms “overbite” and “underbite” define opposing relationships along the anteroposterior, or horizontal, axis.
A true overbite is the clinical term for the vertical overlap of the upper teeth over the lower teeth. In a healthy bite, the upper teeth cover about 20 to 30 percent of the lower teeth; an overlap greater than this is known as a deep bite.
What is commonly called an overbite often refers to an excessive horizontal protrusion of the upper front teeth beyond the lower teeth, which clinicians call overjet. Normal alignment includes a slight overjet, and a deep overjet is classified as a Class II malocclusion.
An underbite, or Class III malocclusion, is the inverse of an overjet, where the lower front teeth or jaw extend in front of the upper teeth. This condition is also known as a negative overjet or anterior crossbite, indicating the lower jaw is positioned too far forward relative to the upper jaw.
The Conflict of Overbite and Underbite
The reason an individual cannot have both an overbite and an underbite is rooted in the definition of the horizontal jaw relationship. Overjet (Class II) defines a scenario where the upper jaw is positioned ahead of the lower jaw. Underbite (Class III) defines the exact opposite, where the lower jaw is positioned ahead of the upper jaw.
These two conditions represent opposite ends of the same anteroposterior spectrum. The jaw can only be positioned forward or backward in relation to the opposing jaw, not both simultaneously. While a person may have a deep vertical overbite, they cannot have a deep overjet and an underbite at the same time, as the presence of one condition inherently negates the other.
Identifying Complex Malocclusion Patterns
The belief that someone has both an overbite and an underbite usually stems from the presence of a complex malocclusion that includes issues in multiple dimensions. For example, a patient might exhibit a deep vertical overbite alongside a posterior crossbite, which is a lateral issue where the upper back teeth bite inside the lower back teeth. This combined issue can create a visually confusing bite pattern that a non-specialist might misinterpret.
These complex cases often involve both skeletal and dental components. A skeletal malocclusion is a misalignment of the jaw bones themselves, while a dental malocclusion involves misaligned teeth within normally positioned jaws. A deep bite (vertical issue) can coexist with severe dental crowding or an open bite in the back teeth, leading to significant functional and aesthetic problems.
Options for Correcting Severe Bite Issues
Addressing severe or complex bite issues requires a thorough diagnosis that examines the relationships in all three planes: vertical, horizontal, and transverse. Standard orthodontic tools like braces and clear aligners are often used to correct dental malocclusions, such as misaligned teeth or minor spacing and crowding issues. These appliances work by applying gradual pressure to reposition the teeth within the dental arches.
For severe skeletal malocclusions, especially those with significant jaw discrepancies, treatment often requires a combined approach. Functional appliances or palatal expanders may be used in growing patients to modify jaw growth. In adults with pronounced skeletal issues, orthognathic surgery, or jaw surgery, is often performed in conjunction with orthodontics to physically reposition the jaw into a correct alignment. This interdisciplinary management is necessary to achieve a stable, functional, and aesthetically balanced outcome.