The relationship between a person’s upper and lower teeth is essential for proper chewing, speaking, and jaw health. Orthodontists assess dental alignment using specific measurements, one of the most significant being the overjet. This measurement provides a quantitative look at how the front teeth align horizontally.
What Overjet Is and the Normal Measurement
Overjet refers to the horizontal distance between the biting edge of the upper front teeth and the front surface of the lower front teeth when the jaw is closed. This distance is measured in millimeters using a dental probe or caliper.
The term overjet is often mistakenly interchanged with overbite, but they describe different dimensions of the bite. Overjet measures the horizontal projection of the upper teeth, while overbite measures the vertical overlap of the upper teeth over the lower teeth. The standard range for a normal overjet in adults and children is between 2 and 4 millimeters. If the measurement falls within this range, the alignment is classified as a balanced dental relationship.
When Overjet Becomes a Problem
An overjet measurement that falls outside the normal 2 to 4 millimeter range indicates a malocclusion, which can lead to various functional issues. The two main types of abnormal overjet are excessive overjet and negative overjet. Excessive overjet occurs when the upper front teeth protrude too far forward, sometimes reaching 8 to 10 millimeters or more, often referred to as “buck teeth.”
This excessive protrusion increases the risk of dental injury, as the front teeth are more susceptible to being chipped or fractured from impact. Severe excessive overjet can also impair the ability to close the lips completely, leading to mouth breathing and a higher risk of tooth decay due to a dry mouth. Functional problems, such as difficulty with chewing and certain speech impediments like lisping, may also develop.
Conversely, a negative overjet, also called an anterior crossbite or underbite, occurs when the lower front teeth extend horizontally past the upper front teeth. This reverse alignment can be caused by a prominent lower jaw or an underdeveloped upper jaw, known as a skeletal discrepancy. Consequences of a negative overjet include abnormal wear patterns on the teeth and functional difficulties with biting and chewing. Both excessive and negative overjet can be influenced by underlying factors, including genetics, jaw size mismatches, and childhood habits such as prolonged thumb-sucking or pacifier use.
Common Approaches to Correction
Correction of an abnormal overjet is managed by an orthodontist and depends on the severity of the misalignment and the patient’s age. For growing children, treatment involves functional appliances to guide jawbone growth. Appliances like headgear or a Herbst appliance can encourage forward growth of a retruded lower jaw or restrict the forward growth of the upper jaw.
For adolescents and adults, non-surgical options reposition the teeth within the jaw arches. These include traditional metal braces or clear aligner systems, which apply consistent forces to gradually shift the teeth into the correct horizontal alignment. Orthodontic elastics, worn with braces or aligners, can apply additional force to reduce the horizontal distance. In cases of severe skeletal discrepancy that cannot be corrected by moving the teeth alone, orthognathic surgery may be necessary to reposition the upper or lower jaw.