Overjet describes the horizontal relationship between the upper and lower front teeth. It refers to how far the upper front teeth extend forward beyond the lower front teeth when the jaws are closed. This horizontal overlap is a natural and expected feature of a healthy bite.
Understanding Overjet
Overjet is a measurement of the horizontal distance between the upper and lower front teeth. It is typically measured in millimeters, from the labial (outer) surface of the lower incisors to the palatal (inner) surface of the upper incisors, with the teeth in centric occlusion.
Overjet is distinct from overbite. While overjet refers to the horizontal projection, overbite describes the vertical overlap of the upper front teeth over the lower front teeth. An overjet indicates how far forward the upper teeth protrude, whereas an overbite indicates how much the upper teeth cover the lower teeth vertically.
Characteristics of Normal Overjet
A normal overjet signifies an ideal horizontal relationship between the upper and lower front teeth. This typically falls within a range of 1 to 4 millimeters, with 2 to 4 millimeters generally considered optimal.
Visually, a normal overjet means the upper front teeth comfortably sit just in front of the lower front teeth, without excessive protrusion or being in an edge-to-edge position. It enables the lower front teeth to lightly touch the back surface of the upper front teeth when the jaws are closed.
Importance of Normal Overjet
A normal overjet contributes to both the efficient functioning of the mouth and a balanced facial appearance. Functionally, it plays a role in effective biting and chewing by allowing the teeth to shear food properly. This optimal horizontal relationship also protects the lips and tongue from accidental biting during chewing or speaking.
Beyond function, a normal overjet supports clear speech and contributes to a balanced facial profile. When the upper and lower teeth align harmoniously, it helps maintain the natural contours of the face. It also contributes to a pleasing smile.
Variations from Normal
When the overjet deviates from the normal range, it can result in various dental misalignments. An “excessive overjet” occurs when the upper front teeth protrude significantly more than the typical 2-4 millimeters. This can exceed 6 millimeters in more severe cases. An excessive overjet can lead to difficulties in biting or chewing certain foods and may increase the risk of injury to the protruding upper front teeth.
Conversely, an “anterior crossbite” represents a negative overjet, where one or more lower front teeth protrude in front of the upper front teeth. Variations from a normal overjet, whether excessive or a crossbite, can affect speech clarity, contribute to jaw discomfort, and lead to uneven wear on the teeth.