An overbite is a common dental misalignment, or malocclusion, where the upper teeth extend significantly beyond the lower teeth. A slight overlap of two to three millimeters is considered normal for proper function. An overbite occurs when this vertical overlap becomes excessive. Understanding the underlying causes is the first step toward addressing this treatable condition.
Understanding the Types of Overbite
The term “overbite” technically refers to a deep bite, which is an excessive vertical overlap of the upper teeth over the lower teeth. This means the upper front teeth cover too much of the lower front teeth when the mouth is closed, sometimes fully hiding them. A deep bite is diagnosed when the upper teeth cover more than three millimeters of vertical overlap, or more than a quarter of the lower teeth.
A distinct, though related, condition is overjet, sometimes incorrectly called a horizontal overbite. Overjet involves the horizontal projection of the upper front teeth outward past the lower teeth. This protrusion is diagnosed when the distance between the upper and lower front teeth exceeds two to three millimeters. Both a deep bite and an overjet can occur simultaneously, and orthodontists categorize both as Class II malocclusions.
Inherited and Skeletal Causes
The primary causes of an overbite are rooted in genetics and the physical structure of the jaws and teeth. These skeletal factors involve the underlying bone structure of the face. A Class II malocclusion, the technical category for most overbites and overjets, is associated with a discrepancy in jaw size or position.
This disparity often involves an underdeveloped lower jaw (mandible) positioned too far back relative to the upper jaw (maxilla), a condition known as mandibular retrognathism. Conversely, the upper jaw may be positioned too far forward, or a combination of both issues may exist. Studies suggest that around 40% of malocclusions are influenced by inherited factors, with the genetic component being stronger for the skeletal pattern.
Genetic predisposition also influences the size of the teeth relative to the jawbones, leading to crowding or spacing issues that contribute to misalignment. The overall craniofacial structure, including the length of the cranial base and the angle of the jaw, can be genetically determined, affecting the final positioning of the teeth. A Class II malocclusion can be passed down as a polygenic trait, meaning it is caused by the interaction of multiple genes.
Acquired Behavioral Factors
Beyond genetics, certain prolonged habits and environmental pressures can physically alter the alignment of the teeth and jaws, leading to an acquired overbite or overjet. One recognized behavioral cause is prolonged thumb or finger sucking that continues past early childhood, typically past the age of three or four. The mechanical force applied pushes the upper teeth forward and can restrict the proper development of the dental arch.
Similarly, the extended use of pacifiers or bottles can exert consistent pressure that influences the alignment of erupting teeth. The duration and intensity of these non-nutritive sucking habits are directly related to the severity of the resulting malocclusion. This constant pressure tends to push the upper teeth into a horizontal protrusion, or overjet.
Another contributing factor is tongue thrusting, also called reverse swallowing, where the tongue pushes against the front teeth during swallowing or speaking. The tongue’s constant, repetitive force can prevent the front teeth from maintaining their correct position, often resulting in an open bite or an increased overjet.
Premature Tooth Loss
The premature loss of primary (baby) teeth can also disrupt the natural spacing required for the permanent teeth to erupt correctly. When a primary tooth is lost too early, the adjacent teeth can drift into the empty space. This causes a lack of room for the permanent tooth and potentially shifts the bite relationship.
When to Seek Professional Guidance
An uncorrected overbite can result in several functional and health issues, including abnormal wear on the tooth enamel, jaw pain, and trauma to the gum tissue. For children, an initial orthodontic evaluation is recommended around the age of seven. This timing is important because the permanent six-year molars have usually erupted, and the fundamental bite pattern is established.
An early assessment allows a professional to monitor the developing bite and identify any skeletal or habit-related issues, even if immediate treatment is not needed. Intervening while a child’s jaw is still growing can guide development and prevent a more severe problem later. For adults, seeking guidance is advisable if they experience difficulty chewing, chronic jaw discomfort, or visibly worn teeth. A dental professional uses visual examinations and X-rays to determine the extent of the skeletal and dental contribution to the overbite.