After growth has completed, either the upper or lower jaw may be disproportionately small or large. In addition to size discrepancies, the relative position of both jaws plays an important role — distinguishing between a receding jaw and one that protrudes too far forward (prognathism). During the bite test, the type of jaw relationship is determined, which allows us to identify whether the condition is an underbite or an overbite.
The surgical objective is to reposition the upper or lower jaw to correct the imbalance so that the teeth meet in perfect alignment. Equal emphasis is placed on achieving a harmonious facial appearance and maintaining optimal jaw joint (TMJ) function.
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Underbite: Prognathism
From a clinical standpoint, a distinction is made between a true and a pseudo-underbite. The most common presentation is a combination of both, characterised by an elongated lower jaw often accompanied by an overly prominent chin and a comparatively small upper jaw. Patients and observers usually perceive the strikingly long lower jaw or the prominent lower lip, while the midface appears flat — a facial type sometimes described as a dish face or concave profile. Pronounced nasolabial folds and an elongated, prominent nose further contribute to the angular, firm appearance of the face.
The exact diagnosis can only be made after a detailed cephalometric analysis, using a digital lateral skull X-ray (teleradiograph) processed with computer software to assess the precise position of the jaws.
When biting, the characteristic reversed overlap of the front teeth becomes visible. If the posterior teeth are also affected, it is referred to as a circular crossbite. This occurs when the upper jaw is too narrow or the lower jaw too wide (see Crossbite). Only after the analysis of plaster jaw models and X-ray evaluations can the underlying cause be fully identified.
From a functional perspective, patients with an underbite often experience difficulties when biting and chewing. This is frequently accompanied by tongue dysfunction, restricted nasal breathing, and increased mouth breathing. These symptoms are rarely associated directly with the malocclusion itself. Occasionally, however, temporomandibular joint (TMJ) issues occur, most notably clicking or popping sounds caused by disc displacement.
Overbite: Increased Overjet
This type of jaw misalignment is one of the most common malocclusions. Normally, the upper front teeth rest on the lower front teeth at a specific physiological angle, ensuring proper alignment between the jaws. If lower jaw growth is inhibited during development, a retruded lower jaw (retrognathia) may form. This condition manifests as an enlarged overbite and reduced mutual support between the upper and lower front teeth.
Typical dental signs include forward-tilted and overlapping lower incisors. In pronounced cases, the lower lip can become trapped between the upper and lower front teeth, sometimes pushing the upper front teeth further forward. If the patient also has a receding chin, the retruded jaw becomes particularly evident — a combination known as retrognathia with reduced chin prominence (receding chin). In more severe cases, a narrow upper jaw may also be present. For aesthetic balance, a chin correction procedure may therefore be recommended in addition to jaw repositioning.
Depending on the degree of overbite, effective biting may only occur when the lower jaw is actively pushed forward. Patients often perform this movement unconsciously, placing significant strain on the temporomandibular joints. This excessive stretching of the joint capsule and ligaments can cause irritation and inflammation, increasing the risk of disc displacement (disc luxation). Depending on the severity, this may involve partial or complete forward displacement of the disc, with or without spontaneous repositioning.
Chronic dysfunction of the TMJ can lead to structural degeneration of the joint and eventually osteoarthritis. This can cause various symptoms such as clicking, grinding, pain while chewing, or restricted mouth opening — collectively referred to as temporomandibular disorder (TMD). Therefore, before initiating corrective treatment for the malocclusion, a thorough radiological and functional TMJ assessment should be conducted. Based on the findings, a suitable bite splint therapy may be prescribed as a pre-treatment measure to relieve pressure on the joints.
