Facial analysis relies on a system of specific reference points, known as anthropometric landmarks, to understand the structure and proportions of an individual’s face. These points allow medical and aesthetic professionals to precisely measure and compare facial features, moving beyond subjective observation to objective data. By establishing these standardized measurements, practitioners can accurately assess growth, diagnose structural imbalances, and plan corrective treatments. The stomion is one such marker, important for the lower third of the face, holding implications for both function and aesthetics.
Anatomical Location and Definition
The stomion is defined as a soft tissue landmark, meaning it is located on the skin and muscle rather than on the underlying bone. Specifically, it is the precise midpoint of the horizontal labial fissure—the line where the upper and lower lips meet. This point is recorded when the facial muscles are at a relaxed, resting state and the lips are gently closed. It exists on the mid-sagittal line, an imaginary vertical plane that divides the face into two symmetrical halves.
The landmark is often abbreviated as ‘St’ or ‘Stm’ in clinical documentation. It is distinguished from other nearby soft tissue points like labrale superius (midline point on the upper lip’s vermilion border) or labrale inferius (midline point on the lower lip’s vermilion border). Due to its location at the interface of the two lips, the stomion serves as a direct indicator of the vertical relationship between the upper and lower lip tissues. Its definition assumes a complete labial seal, though if the lips do not meet, the point may be conceptually split into superior and inferior versions for measurement purposes.
How the Stomion is Used in Clinical Analysis
The stomion is a foundational measurement in the assessment of the face, particularly in fields focused on dentofacial structures. Practitioners utilize advanced imaging techniques to map this landmark and its relationships to surrounding features. Historically, this involved cephalometric radiography, where a standardized X-ray of the head was taken and the soft tissue profile traced. Newer methods employ 3D facial scanning or cone-beam computed tomography (CBCT) to capture the soft tissue profile with greater accuracy, allowing for three-dimensional analysis.
This landmark is a key reference for evaluating the vertical dimensions of the lower face. Upper lip length is calculated as the vertical distance between the subnasale (the base of the nose) and the stomion. Lower lip height is measured from the stomion to the soft tissue menton (the lowest point of the chin). By comparing these vertical measurements to established population norms, clinicians determine if the lower third of the face is proportionally balanced, excessively long, or unusually short.
The stomion’s vertical position in relation to the upper incisor teeth is a widely used metric known as incisor display. This measurement assesses how much of the upper central incisors are visible when the lips are at rest, which is an important factor in smile design. Measurement involves calculating the distance between the stomion and the incisal edge of the maxillary central incisor. An excessive display of the upper incisors, or conversely, no display at all, helps guide orthodontic or maxillofacial surgical planning.
Significance for Lip Competence and Facial Harmony
The position of the stomion is directly related to lip competence, the ability to maintain a relaxed, sealed mouth posture without muscular strain. An ideal stomion position allows the lips to meet passively, indicating competent lips. If the upper and lower lips fail to meet at the stomion when the face is at rest, the patient has incompetent lips, requiring conscious effort or muscle strain to achieve a seal.
Lip incompetence can be a sign of underlying skeletal or dental issues, such as excessive vertical growth of the upper jaw or protrusion of the front teeth. This prevents the lips from easily closing and can have functional implications, including issues with breathing, swallowing, and speech. The stomion’s resting position is therefore a functional diagnostic indicator. The position of the stomion also impacts the overall aesthetic appearance of the lower face, contributing to facial harmony.
The vertical placement of the stomion dictates the perceived length of the upper and lower lips, which is a major factor in determining a balanced appearance. In surgical contexts, such as orthognathic surgery (jaw surgery), the stomion is tracked as a predictive marker for the final soft tissue outcome. When the underlying jaw bones are repositioned, the soft tissues, including the lips, move predictably. Planning a vertical movement of the jaw requires precise calculation of the resulting change in the stomion’s position to ensure both aesthetic balance and functional lip competence post-surgery.