An overjet is a type of dental misalignment, or malocclusion, where the upper front teeth horizontally project significantly outward beyond the lower front teeth. This horizontal protrusion is often called “buck teeth.” While a small amount of horizontal overlap is normal, an excessive overjet represents a deviation from ideal alignment. It is caused by skeletal, dental, and environmental factors that push the upper teeth or jaw forward.
Understanding the Difference Between Overjet and Overbite
The terms overjet and overbite are frequently confused, but they describe two distinct types of dental overlap. Overjet refers to the horizontal distance, or protrusion, between the upper and lower incisors. It measures how far the upper teeth stick out in front of the lower teeth in a front-to-back direction.
Overbite, conversely, describes the vertical overlap of the teeth, indicating how much the upper front teeth cover the lower front teeth when the jaw is closed. An easy way to distinguish them is to think of “jet” as the horizontal projection and “bite” as the vertical dimension. Both conditions can exist simultaneously, but they are measured and treated differently by orthodontists.
Orthodontists precisely measure the overjet in millimeters (mm) by finding the distance from the back surface of the upper incisor to the front surface of the lower incisor. A healthy, normal overjet typically measures between 1 and 3 mm. An overjet is considered excessive when this horizontal distance exceeds 2 to 4 mm, signaling a misalignment that may require intervention.
Common Causes and Associated Health Concerns
The causes of an increased overjet can be broadly categorized into skeletal and habitual factors. Skeletal factors involve the inherent size and position of the jawbones, often having a genetic component. This can manifest as a lower jaw (mandible) that is underdeveloped and positioned too far back, or an upper jaw (maxilla) that is too prominent.
Habitual factors, especially those present during childhood development, also play a significant role in pushing the teeth forward. Prolonged thumb or finger sucking past the age of four can exert continuous pressure on the upper front teeth, causing them to flare outward. Tongue thrusting, where the tongue pushes against the front teeth during swallowing or rest, and extended pacifier use can similarly contribute to the development of an overjet.
An untreated overjet carries several functional and health consequences that extend beyond cosmetic concerns. The most serious risk is an increased susceptibility to dental trauma for the protruding upper incisors. Research suggests that an overjet greater than 4 mm can double the risk of incisor injury and chipping from accidents or falls.
The misalignment can also interfere with proper functional movements, leading to difficulties with efficient chewing and potentially causing speech impediments like lisping. When the upper teeth protrude so far that the lips cannot comfortably close around them, it can lead to chronic mouth breathing and a dry mouth. This reduction in protective saliva flow increases the risk of tooth decay and gum disease.
Orthodontic Solutions for Correction
Correcting an overjet often involves a comprehensive orthodontic strategy that is tailored to the patient’s age and the severity of the skeletal discrepancy. For growing children and adolescents, treatment frequently involves functional appliances designed to modify jaw growth. These removable or fixed devices encourage the lower jaw to grow forward or restrict the forward growth of the upper jaw, aiming to harmonize the skeletal base.
Traditional fixed braces, which use brackets and wires, are a standard option for correcting the position of the teeth themselves. Braces may be combined with elastic bands to apply force that pulls the upper teeth back or moves the lower teeth forward. Clear aligner systems can also be effective for mild to moderate cases where the problem is primarily dental, involving tooth movement rather than major jaw repositioning.
In cases of significant skeletal discrepancy in adults, where jaw growth is complete, orthodontic camouflage involving tooth extraction may be considered to create space to retract the upper teeth. However, the most severe cases may require a combined approach of orthodontics and orthognathic surgery, which physically repositions the jawbones. Early intervention during childhood is often recommended to achieve the most stable results and prevent the need for more complex surgical procedures later in life.