An overbite, often described as a “deep bite,” is a common dental misalignment where the upper front teeth excessively overlap the lower front teeth vertically. While some overlap is necessary for proper function, an exaggerated overbite is classified as a form of malocclusion, or “bad bite.” This condition is more than a cosmetic issue; it affects chewing, speaking, and oral health. The causes of an overbite in adults are varied, stemming from inherited structural issues to environmental factors that persist over a lifetime.
Understanding Malocclusion and Overbite Types
Malocclusion is a general term describing any improper positioning of the teeth when the jaws are closed. An overlap is considered excessive and categorized as an overbite (or deep bite) when the upper teeth cover the lower teeth by more than 2 to 4 millimeters. It is important to distinguish an overbite from an overjet, which refers to a horizontal protrusion where the upper front teeth stick out diagonally beyond the lower teeth. Overbites are classified as either dental, meaning the issue lies solely with the teeth, or skeletal, indicating a structural imbalance in the jawbones. A severe overbite is frequently associated with a Class II malocclusion, defined by the upper arch being positioned too far forward relative to the lower arch.
Foundational Skeletal and Genetic Factors
The fundamental causes of an overbite relate to the underlying bone structure of the face and jaw, established through genetics. Heredity plays a significant role in determining the size and shape of the maxilla (upper jaw) and the mandible (lower jaw), often resulting in an inherited skeletal discrepancy.
Specific jaw imbalances create the vertical misalignment. One common structural issue is a disproportionately small or set back lower jaw, known as mandibular retrognathism. Conversely, an overly large or forward-positioned upper jaw (maxillary prognathism) can also contribute to the excessive overlap. These skeletal factors persist into adulthood and represent a primary structural cause of the condition.
Environmental and Functional Causes in Adulthood
While skeletal factors are fixed, environmental and functional issues can cause or worsen an overbite in adulthood by modifying the position of the teeth. Chronic, persistent habits exert pressure on the teeth, gradually shifting their alignment. For instance, chronic tongue thrusting, where the tongue pushes against the front teeth during swallowing, can force the upper teeth forward or prevent the lower teeth from erupting fully.
Other habits contributing to adult overbites include excessive nail biting or habitually chewing on pens. These actions apply prolonged forces that change the dental alignment over time. Furthermore, the long-term loss of posterior (back) teeth can cause the overall bite to collapse or deepen. Without the stable support of the back molars, the front teeth carry more load, causing them to over-erupt and increase the vertical overlap.
Teeth grinding, termed bruxism, also contributes to overbite progression. Bruxism causes excessive wear on the biting surfaces, reducing the vertical dimension. This reduction forces the lower jaw to close further, effectively deepening the overbite. Finally, poorly designed or aged dental restorations, such as crowns or fillings, can slowly destabilize the occlusion.
Associated Health Concerns and Complications
An excessive overbite is not simply an aesthetic problem; it predisposes a person to several health complications. Primary among these is accelerated wear and tear on the teeth. The constant, forceful contact between the overlapping front teeth can lead to premature enamel erosion, chipping, and fracturing. In severe cases, the lower front teeth may repeatedly traumatize the gum tissue or the roof of the mouth behind the upper teeth.
The strain from an improper bite can also affect the temporomandibular joints (TMJ). This misalignment often results in temporomandibular disorders (TMD), characterized by jaw pain, headaches, and difficulty chewing. Furthermore, a recessed lower jaw associated with a deep bite can contribute to breathing difficulties, especially during sleep, increasing the risk of obstructive sleep apnea.