An overbite is the vertical overlap of the upper front teeth over the lower front teeth. This arrangement is necessary for a properly aligned bite, allowing the front teeth to function correctly during chewing and protecting the soft tissues of the mouth. The amount of overlap must fall within a specific range, as too much or too little overlap can cause significant functional and health problems. Understanding this normal range helps determine if a bite requires professional evaluation.
Understanding Vertical Overlap and Overjet
The alignment of the front teeth is measured in two primary dimensions: vertical and horizontal. The term overbite is used in orthodontics to describe the vertical measurement, indicating how much the upper teeth cover the lower teeth when the back teeth are closed together. This vertical relationship is also sometimes called the deep bite.
In contrast, overjet describes the horizontal measurement: the distance the upper front teeth protrude forward relative to the lower front teeth. Although the public often uses “overbite” to describe teeth that stick out, this technically refers to an excessive overjet. Both measurements are crucial for a comprehensive assessment of dental alignment, known as malocclusion.
Orthodontists quantify overbite and overjet using specific tools, often measuring in millimeters or as a percentage of coverage. The overjet (horizontal measurement) is taken from the cutting edge of the upper incisor to the front surface of the lower incisor. The overbite (vertical measurement) quantifies the extent of the overlapping. A person can have an excessive measurement in one dimension while the other remains within normal limits.
The Acceptable Range for Overbite
A small amount of vertical overlap is considered functionally ideal for a healthy bite. This slight overlap allows the front teeth to efficiently shear food and protects the back teeth from excessive wear during jaw movements. The specific range considered normal or ideal in standard orthodontic practice is narrow.
An optimal overbite is defined as a vertical overlap of approximately 2 to 4 millimeters (mm). Expressed as a percentage, this means the upper teeth cover the lower teeth by about 10% to 30%. This range ensures the upper and lower teeth meet in a way that distributes chewing forces evenly across the entire dental arch.
Any measurement outside this ideal 10% to 30% range is classified as a malocclusion, or a “bad bite.” If the vertical overlap is less than 10%, it is an insufficient overbite, which can result in an open bite where the front teeth do not meet. Conversely, overlap exceeding 4 mm or 30% is classified as an excessive overbite, commonly known as a deep bite.
Health and Functional Issues of Excessive Overlap
Excessive vertical overlap (a deep bite) can lead to several mechanical and functional issues. In a severe deep bite, the lower front teeth may contact the sensitive gum tissue behind the upper front teeth, known as gingival impingement. This repeated trauma can cause painful sores, gum recession, and damage to the supporting structures of the upper teeth.
The misalignment also results in uneven tooth contact, causing premature wear on the biting surfaces. Constant grinding and impact wear down the protective enamel, making teeth more susceptible to decay and sensitivity. Over time, this wear compromises the structural integrity of the front teeth.
Excessive overlap can place strain on the temporomandibular joint (TMJ) and associated jaw muscles. This strain may contribute to symptoms like chronic jaw pain, headaches, and earaches, collectively known as temporomandibular disorders. Additionally, a deep bite can interfere with the ability to chew food properly, making certain foods difficult or painful to eat.
Issues Related to Excessive Overjet
Extreme horizontal overlap (overjet) presents its own functional concerns. An increased overjet, where the upper teeth protrude significantly, increases the risk of traumatic dental injury because the lips cannot fully cover and protect the teeth. When the horizontal gap exceeds 4 millimeters, the risk of incisor trauma is estimated to be approximately double.
Severe horizontal protrusion can also lead to difficulties with speech articulation, especially sounds requiring precise tongue and teeth positioning. If the protrusion prevents the lips from closing completely, the mouth can become dry. This reduces the protective properties of saliva and increases the risk of tooth decay and gum issues. If either the vertical or horizontal overlap falls outside the optimal 2 to 4 mm range, consultation with an orthodontist is recommended to prevent long-term complications.