The stomion refers to an anatomical point on the face, representing the natural meeting point of the upper and lower lips when the mouth is gently closed and at rest. It is a soft tissue landmark that plays a role in facial aesthetics and function. This point holds significance in various medical and dental fields due to its relationship with other facial structures and its impact on facial harmony. Understanding the stomion is foundational for assessing and planning treatments related to the mouth and surrounding areas.
Understanding the Stomion’s Location
The stomion is located at the midpoint of the oral fissure, the opening between the upper and lower lips when closed. It is situated along the mid-sagittal line, an imaginary vertical line dividing the face into two symmetrical halves. It can be further defined by its superior and inferior components: the stomion superioris (Sts) is the most inferior point of the upper lip in the mid-sagittal plane, and the stomion inferioris (Sti) is the most superior point of the lower lip in the mid-sagittal plane.
The stomion’s position is considered in relation to other prominent facial landmarks. For instance, the subnasale (Sn) is the midpoint where the nose meets the upper lip, while the soft tissue pogonion (Pg) is the most anterior midpoint of the chin. The distance between the subnasale and the stomion superioris defines the length of the upper lip. The stomion’s exact position can vary among individuals, influenced by age, sex, and ethnicity.
Why the Stomion Matters in Healthcare
The stomion’s location and its relationship to surrounding structures make it an important reference point in healthcare disciplines like dentistry, orthodontics, and plastic surgery. Its measurement is used for diagnosis, treatment planning, and evaluating facial aesthetics and functional outcomes. For example, in orthodontics, the stomion is considered when assessing occlusion and facial aesthetics to plan effective treatment strategies.
One application involves assessing incisor display, which refers to how much of the upper front teeth are visible when the lips are at rest or during a smile. Ideal incisor display shows about 2-4 millimeters of the upper incisors at rest, with full crown exposure and approximately 2 millimeters of gingival margin visible during a full smile. Deviations from these ideal measurements, such as excessive gingival display or inadequate tooth visibility, can be linked to the stomion’s position relative to the teeth.
The stomion also plays a role in evaluating lip competence, which describes the ability of the lips to meet and seal without strain when the jaw is relaxed. Incompetent lips, which do not naturally touch, may indicate underlying issues like anatomically short lips or protruded maxillary incisors. This assessment helps guide corrective procedures, such as orthognathic surgery, where the stomion’s position is considered for achieving proper bite alignment and facial profile aesthetics. Measurements are performed through visual assessment during clinical examination or with methods like anthropometric analysis using calipers or cephalometric analysis using radiographic images.