The human mouth consists of the upper dental arch, fixed to the skull, and the lower dental arch, part of the movable mandible. The relationship between these two arches when the mouth is closed is known as dental occlusion. This alignment is not merely a matter of aesthetics; it is fundamental to the ability to chew, speak, and maintain the long-term health of the teeth and jaw joints.
Understanding Proper Occlusion
Yes, your top teeth should overlap your bottom teeth, but only by a specific, small amount. This slight overlap is the standard for a healthy, functional bite, technically referred to as a Class I occlusion. This ideal relationship is measured in two dimensions: vertical and horizontal.
The vertical overlap, or overbite, describes how much the top front teeth cover the bottom front teeth when the back teeth are closed. For a balanced bite, the upper teeth should cover the lower teeth by approximately 20 to 30% of the lower crown height, or 1 to 2 millimeters. This gentle coverage protects soft tissues, such as the lower lip and gums, from being bitten during chewing.
The horizontal overlap, or overjet, is the measurement of the space between the lower and upper front teeth. In a proper occlusion, the upper teeth should sit slightly in front of the lower teeth, ideally by about 1 to 3 millimeters. This small horizontal gap and the vertical overlap work together to ensure that the molars can shear and grind food efficiently while the front teeth provide guidance during jaw movement.
Classifying Malocclusions
When the vertical or horizontal overlap deviates significantly from the ideal measurements, the condition is classified as a malocclusion. These misalignments are often described using the Angle classification system, which focuses on the front-to-back relationship of the molars and incisors. The most common form of malocclusion is Class I, where the molar relationship is correct, but the teeth are crowded or misaligned.
A Class II malocclusion is characterized by a high overjet, where the upper teeth and jaw project forward relative to the lower jaw. This excessive overlap often results in the appearance of “buck teeth” and leaves the upper incisors vulnerable to trauma. Conversely, a Class III malocclusion, commonly called an underbite, occurs when the lower jaw and teeth protrude, resulting in a reversed horizontal overlap where the bottom front teeth sit in front of the top front teeth.
Vertical discrepancies also define specific malocclusions. A deep bite is an excessive vertical overlap where the upper teeth cover more than 50% of the lower teeth, sometimes causing the lower teeth to bite directly into the gum tissue behind the upper teeth. At the other extreme is an open bite, a condition where the front teeth—and sometimes the back teeth—do not touch at all when the jaw is closed.
Functional Impacts of Misalignment
The consequences of an improper overlap extend beyond just the appearance of the smile, impacting overall oral function and health. When the teeth do not meet correctly, the forces generated during chewing are not distributed evenly across the dental arches. This uneven distribution can lead to wear patterns on the enamel, causing some teeth to thin or chip prematurely.
Malocclusion also places stress on the temporomandibular joints (TMJ), which connect the jawbone to the skull. This chronic strain can contribute to symptoms like headaches, facial pain, and clicking or popping sounds in the jaw joint. Furthermore, severe misalignments can interfere with articulation, sometimes causing speech impediments.
In cases of high overjet, the protruding upper teeth lack the protective cushioning of the lower lip, increasing the risk of fracture or displacement. An inadequate overlap can also compromise the ability to fully close the lips, leading to habitual mouth-breathing which dries out the mouth and may increase the risk of certain gum conditions.
Orthodontic Interventions
Restoring the correct vertical and horizontal overlap is the primary goal of orthodontic treatment for malocclusion.
Traditional Braces
For many patients, traditional braces use brackets and archwires to apply continuous force, gradually moving teeth to reduce the overjet or overbite. This process is often aided by elastic bands worn between the upper and lower arches to guide the jaws into a more favorable relationship.
Clear Aligners
Clear aligners offer another path, utilizing a series of custom-designed, incremental trays to exert targeted pressure on the teeth. While effective for mild to moderate dental misalignments, clear aligners may require the use of small, tooth-colored attachments to achieve the complex movements needed to correct significant vertical overlap.
Skeletal Correction
For younger patients whose jaws are still developing, palatal expanders can be used to widen a narrow upper jaw, addressing transverse issues like a crossbite and making space for proper tooth eruption. When the malocclusion is due to a severe skeletal discrepancy—meaning the jaw bones themselves are disproportionately sized or positioned—orthognathic surgery may be necessary. This surgical procedure involves the precise repositioning of the maxilla or mandible to achieve a stable, functional overlap that neither stresses the joints nor compromises the teeth.