A prominent upper lip is a common observation rooted in the underlying structure of the facial skeleton and the alignment of the teeth. This difference in lip projection is related to a discrepancy in the horizontal relationship between the upper jaw (maxilla) and the lower jaw (mandible). The soft tissues of the lips drape over this foundational framework, making any skeletal or dental misalignment visible in the profile and at rest. Understanding this phenomenon involves examining whether the issue originates from the jaw bones, the teeth, or the surrounding muscles and habits.
Skeletal Basis: Jaw Position
The sagittal, or front-to-back, positioning of the jaw bones is a primary cause of upper lip prominence. This structural difference is diagnosed as a Skeletal Class II pattern, meaning the upper jaw is positioned forward relative to the lower jaw. One presentation is mandibular retrusion, where the lower jaw is set back too far beneath the skull base. When the mandible is positioned backward, the lower lip and the teeth it supports are also retracted, making the upper lip appear to protrude, even if the maxilla is normally positioned.
Another skeletal factor is maxillary protrusion, which involves an upper jaw set too far forward. In this instance, the maxilla itself has overgrown or developed anteriorly, pushing the entire upper dental arch and overlying soft tissues outward. Both mandibular retrusion and maxillary protrusion result in a convex facial profile, where the lips strain to meet or rest in an unbalanced position. The degree of this bony discrepancy determines the severity of the lip imbalance and often dictates the complexity of any necessary correction.
Dental Factors: Tooth Alignment
The individual positioning of the teeth can cause the upper lip to protrude, even if the jaw bones are well-aligned. This dental component is defined by overjet, the horizontal overlap between the upper and lower front teeth. A normal overjet is between one and three millimeters, but when this measurement significantly increases, the upper incisors push the lip forward. Protruding upper incisors are often referred to as “buck teeth” and are a common feature of the Class II Division 1 malocclusion.
A condition called proclination describes the forward tilting or angling of the upper front teeth. The crowns of these teeth can be tipped outward toward the lip, physically displacing the upper lip tissue and causing it to appear more prominent. While a skeletal issue involves the position of the entire jaw bone, a dental issue stems from the angle of the teeth within the bone. It is common for patients to have a combination of both skeletal and dental factors.
Myofunctional and Soft Tissue Influences
A condition known as lip incompetence describes the inability to naturally bring the lips together at rest without straining the surrounding mentalis muscle in the chin. This inability to seal the lips is often exacerbated by underlying skeletal or dental protrusion, but it can also be influenced by abnormal muscle patterns. The lower lip can sometimes catch behind the protruding upper incisors, creating a “lip trap” that further pushes the upper teeth forward over time.
Chronic mouth breathing, often due to nasal airway obstruction, can alter facial muscle posture and contribute to lip prominence. When the mouth is habitually open, the lower jaw tends to drop, and the tongue rests lower in the mouth. This low tongue posture and open-mouth rest position can negatively influence the development of the upper jaw and dental arch. Furthermore, childhood habits like prolonged thumb-sucking or tongue thrusting apply constant pressure, which can proclinate the upper incisors and contribute to the lip imbalance.
Addressing Protrusion: Treatment Options
Correcting a prominent upper lip requires addressing the underlying dental or skeletal cause. Orthodontic treatment is the first line of approach for dental issues, using fixed appliances like braces or clear aligners to retract the upper teeth and reduce the overjet. In cases with significant proclination, the orthodontist may need to create space in the arch, sometimes requiring the extraction of certain teeth to allow the front teeth to be pulled backward into a more favorable position. Modern techniques utilize temporary anchorage devices, or miniscrews, which provide stable points to anchor retraction forces, improving the efficiency of tooth movement.
For severe skeletal discrepancies, where the jaw bone relationship is significantly misaligned, orthognathic surgery is often necessary. This procedure involves surgically repositioning the maxilla or mandible to correct the foundation of the face. Surgical intervention is usually performed in conjunction with orthodontics, with the braces used before and after the surgery to ensure the teeth align properly once the jaws are repositioned.
The timing of intervention is also a factor, with certain appliances designed to modify jaw growth in younger, still-growing patients. For adults, the focus shifts to a combination of tooth movement and surgical correction, depending on the severity of the skeletal issue. While procedures like lip fillers can temporarily alter the volume of the lips, they do not correct the underlying dental or skeletal misalignment.