A smile is commonly called a “gummy smile” when two millimeters or more of gum tissue are visible above the upper teeth during a full smile. This characteristic results from several underlying biological and anatomical structures. The causes are varied, ranging from the structure of the jawbone to the muscles controlling the upper lip. Understanding the specific mechanism is necessary because the approach to correction depends entirely on the structural origin of the display.
Skeletal and Dental Positioning
The underlying bone structure of the face can be a primary determinant of a gummy smile. One significant skeletal cause is Vertical Maxillary Excess (VME), where the upper jawbone, or maxilla, is vertically overdeveloped. This excessive bone height positions the teeth and gums lower down in the face, which results in more gum tissue being exposed when smiling. VME is a developmental condition that is typically genetic in origin and often contributes to a longer, narrower appearance in the lower third of the face.
Another common structural factor is a developmental issue called altered passive eruption. During normal dental development, the gums and the underlying bone recede to fully expose the clinical crown of the tooth. In cases of altered passive eruption, this process fails to complete correctly, leaving too much gum tissue covering the tooth surface. The teeth themselves are of normal length, but they appear short because the gingiva has not migrated to its proper position, creating the illusion of an excessive gum line.
Lip Dynamics and Muscle Activity
For many individuals, the cause lies not in the bone or the teeth themselves but in the muscles that control the upper lip’s movement. The condition is known as a hypermobile or hyperactive upper lip, meaning the lip elevates too high when a person smiles.
Specific muscles, particularly the Levator Labii Superioris Alaeque Nasi (LLSAN) muscle group, contract with too much force or range of motion. This excessive contraction pulls the upper lip border significantly higher than average, revealing the gingiva underneath. A short clinical upper lip length, measured from the base of the nose to the upper lip margin, can also compound this effect. Even with normal muscle function, a shorter lip provides less coverage over the gum line, naturally exposing more tissue upon smiling.
Excessive Gum Tissue
The soft tissue of the gums, known as the gingiva, can itself be the source of the excessive display. This condition is termed gingival enlargement, which involves an actual overgrowth of the gum tissue. This enlargement can stem from localized inflammation, often due to poor oral hygiene and the accumulation of bacterial plaque. In this scenario, the body’s inflammatory response causes the gum tissue to swell and increase in mass.
In other cases, the enlargement is a side effect of certain systemic medications. Drug-induced gingival enlargement is caused by specific classes of drugs, which interfere with the normal cellular processes of the gum tissue. These include anticonvulsants used to manage seizures, immunosuppressants prescribed after organ transplants, and calcium channel blockers used for heart conditions and high blood pressure. The resulting overgrowth covers more of the tooth surface, contributing to the appearance of a gummy smile.
Common Correction Methods
Treatment for excessive gingival display is highly individualized based on an accurate diagnosis of the underlying cause. For muscle-related issues, where a hyperactive lip is the culprit, a non-surgical approach is often the first step. Neuromodulator injections, such as Botox, can be administered directly into the LLSAN muscle group to temporarily relax the muscles. This relaxation reduces the upward pull of the upper lip during a smile, limiting gingival exposure for three to six months before requiring a repeat treatment.
When the cause is excessive gum tissue or altered passive eruption, a periodontal procedure known as crown lengthening is used. This surgical technique involves reshaping the gumline and sometimes removing a small amount of underlying bone to expose the full height of the tooth’s crown. A less invasive version, called a gingivectomy, removes only the soft gum tissue, often using a laser for precision and faster healing. This procedure provides a permanent correction by restoring the correct proportion between the tooth and the gumline.
The most definitive correction is reserved for severe skeletal discrepancies, specifically Vertical Maxillary Excess. This requires orthognathic surgery, performed by a maxillofacial surgeon. The procedure involves surgically repositioning the upper jaw to shorten the vertical dimension of the maxilla, which permanently reduces the visibility of the gums. Because the etiology is often multifactorial, some patients may require a combination of treatments, such as orthodontics followed by a minor soft tissue procedure, to achieve the desired aesthetic result.