An underbite is a condition where the lower jaw and teeth extend forward past the upper jaw when the mouth is closed. This misalignment creates a characteristic appearance where the chin often looks prominent and the lower face appears unbalanced. Correcting an underbite significantly changes a person’s profile and overall facial appearance. This transformation results from establishing the correct structural relationship between the upper and lower jaws. The specific degree of facial change depends directly on the severity of the original misalignment and the method of correction chosen.
The Skeletal and Dental Basis for Facial Change
The distinctive facial appearance of an underbite stems from two primary components: skeletal and dental. The skeletal issue involves a discrepancy in the size or position of the jawbones, often an overgrowth of the lower jaw (mandible) or an underdevelopment of the upper jaw (maxilla). This bony framework dictates the underlying shape of the lower third of the face.
The dental component involves the teeth tilting in an attempt to camouflage the skeletal problem, a process called dental compensation. For instance, the lower front teeth may tilt backward while the upper front teeth tilt forward to maintain contact. Correcting the malocclusion requires repositioning these hard tissues—the jawbones and the teeth—to their proper anatomical relationship.
When the underlying bone structure is moved, the soft tissues of the face, including the lips, cheeks, and chin padding, are carried along. This is the mechanical cause of the facial change. When the lower jaw is moved backward, or the upper jaw is brought forward, the surrounding soft tissue drapes differently over the new foundation. This results in an alteration in the profile, symmetry, and overall harmony of the facial features.
Orthodontic vs. Surgical Correction Paths
The extent of facial change is intrinsically linked to the method used to resolve the underbite. For milder cases where the discrepancy is primarily dental, an orthodontic-only approach is often used, utilizing braces or clear aligners. In these instances, the facial change is typically subtle, mostly affecting the profile’s soft tissue contours. Repositioning the teeth can improve lip posture, allowing the lips to meet more naturally without strain.
This dental correction does not address a significant skeletal imbalance and results in a less pronounced change to the chin and jawline. When the underbite is severe and caused by a major skeletal discrepancy, surgical correction, known as orthognathic surgery, is required. This method involves physically repositioning the jawbones to correct size and position differences.
Common procedures include the Bilateral Sagittal Split Osteotomy (BSSO) to move the lower jaw backward or a Le Fort I osteotomy to advance the upper jaw. This combined surgical and orthodontic path results in the most significant and predictable facial transformation. Moving the skeletal foundation alters the facial structure, creating a new, balanced profile. The planning involves extensive imaging to ensure the surgical movements achieve the desired aesthetic and functional goals simultaneously.
Specific Aesthetic Outcomes
Correcting an underbite replaces a concave profile with one that is more balanced and convex. The most noticeable change occurs in the chin, which often appears less prominent or jutting after the lower jaw is repositioned. This reduction in projection helps to establish a more harmonious facial outline.
The jawline gains improved definition and contour as the lower jaw is set back into its correct position relative to the upper jaw. The soft tissues around the chin tighten, which further enhances the newly established jawline. This structural improvement often reduces the appearance of a heavy or rounded lower face.
Lip posture is significantly improved, moving from a strained or separated appearance to a natural lip seal at rest. The upper lip receives more support from the aligned upper teeth and jaw, enhancing the mid-face region. Although the size of the nose remains unchanged, its relationship to the newly positioned jaw is altered, which can make the nose appear softer or less dominant in the profile.
The Importance of Timing: Correction in Childhood vs. Adulthood
The age at which an underbite is corrected determines both the treatment approach and the nature of the facial change. Early intervention, typically starting around ages seven to ten, capitalizes on active growth and development. Treatment at this stage focuses on growth modification, aiming to redirect or restrict the growth of the jawbones.
Orthodontic appliances like a reverse-pull face mask or specialized expanders are used to encourage the forward growth of the upper jaw while limiting the lower jaw’s growth. Facial changes resulting from this early treatment are integrated gradually as the child develops. This approach can potentially guide the jaws into a correct relationship, often making later surgery unnecessary.
In adulthood, once skeletal growth is complete, the bones are fixed, and growth modification is no longer possible. For adults with a moderate to severe skeletal underbite, correction almost always requires orthognathic surgery. The resulting facial changes are immediate and more pronounced due to the physical repositioning of the mature jawbones. This transformation contrasts with the developmental changes seen in a growing child.