The term “overbite” refers to the vertical overlap between the upper and lower front teeth when the jaw is closed. A slight overlap is normal and necessary for proper dental function, providing stability for chewing and protecting soft tissues. The issue arises when this overlap becomes excessive, a condition often called a deep bite.
Visual Indicators of Excessive Vertical Overlap
Observing the relationship between the upper and lower front teeth while looking in a mirror provides the first indication of a potential issue. In a healthy bite, the upper incisors cover approximately 20% to 40% of the lower incisors when the teeth are closed. This normal overlap typically measures between two and four millimeters. If the upper teeth cover the lower teeth by more than 40%, the overlap is considered excessive, and the lower teeth may appear barely visible or completely hidden. In severe cases, the lower front teeth may even make contact with the gum tissue behind the upper front teeth, which is known as an impinging overbite.
An excessive vertical overlap can also affect the appearance of the lower third of the face, potentially making it look disproportionately short. The jaw may appear slightly receded, and some individuals might notice a deep crease or dimpling in the chin area. This is sometimes caused by the mentalis muscle straining to bring the lips together to achieve a seal.
Physical Symptoms and Functional Issues
Beyond visual cues, an excessive overbite often manifests through noticeable physical symptoms that indicate functional strain on the dental system. One of the most common signs is premature wear on the teeth, specifically the back surfaces of the upper front teeth and the biting surfaces of the lower front teeth. The constant, forceful contact resulting from the deep overlap can lead to enamel erosion over time.
The lower incisors can sometimes bite directly into the gum tissue on the roof of the mouth, or the upper teeth may impact the lower gums. This trauma can cause chronic irritation, inflammation, and potential gum recession around the affected teeth. Severe deep bites can also lead to difficulty chewing certain foods, as the misalignment hinders the proper shearing action of the teeth.
The strain created by an improper bite alignment can contribute to symptoms associated with temporomandibular joint (TMJ) disorders. Patients may experience persistent jaw pain, soreness in the facial muscles, or frequent headaches. Audible clicking or popping sounds when opening or closing the jaw are also common indicators of stress on the joint.
How Professionals Classify Overbite Severity
Dental professionals quantify vertical overlap to accurately assess the severity of the condition. Classification is typically based on a measurement taken in millimeters (mm) or a percentage of the lower incisor crown that is covered by the upper incisor. A measurement greater than four millimeters or an overlap exceeding 40% is generally considered an excessive deep bite.
The condition is often categorized into general levels of severity to guide treatment planning. For instance, a mild overbite might involve less than three millimeters of overlap, a moderate case falls between three and six millimeters, and a severe overbite is classified as more than six millimeters. These classifications can vary slightly depending on the specific diagnostic system used by the practitioner.
To ensure a precise diagnosis, an orthodontist or dentist will utilize diagnostic tools beyond a simple visual exam. Accurate assessment requires taking dental molds, which create a three-dimensional model of the bite, and obtaining radiographs, such as X-rays. These detailed images allow the professional to determine if the issue is primarily caused by tooth position (dental overbite) or a discrepancy in jaw size (skeletal overbite).