A smile showing more gum tissue than expected, known as a “gummy smile” or excessive gingival display, is a common aesthetic concern. While 1 to 2 millimeters of gum exposure is generally considered visually appealing, displaying 4 millimeters or more is often perceived as unbalanced. Excessive gum tissue is caused by a combination of underlying biological and structural variations in the gums, teeth, jawbone, and facial muscles. Understanding the specific cause is the first step in addressing this issue, as the underlying reason dictates the proper course of action.
Excessive Gum Tissue
Increased gum visibility can stem directly from the gingival tissue itself, appearing as an overgrowth or enlargement. This condition is medically termed gingival hypertrophy or gingival hyperplasia, where the tissue swells and extends further down the tooth surface. The most frequent cause of this enlargement is inflammation, particularly chronic gingivitis or periodontitis, often resulting from inadequate oral hygiene. The accumulation of bacterial plaque near the gum line triggers an inflammatory response, causing the tissue to become puffy and overgrown.
Gingival overgrowth can also be a side effect of certain systemic medications. Three main classes of drugs are commonly implicated: anticonvulsants (e.g., phenytoin), immunosuppressants (e.g., cyclosporine, often prescribed after organ transplantation), and calcium channel blockers (e.g., nifedipine, used for high blood pressure or heart conditions). These medications alter the metabolism of gum cells, leading to an excessive buildup of tissue that covers more of the tooth surface. This tissue excess represents a volume increase or swelling of the soft tissue itself.
Tooth Size and Eruption Patterns
Causes can relate to the teeth and how they emerge through the gums, affecting the visible height of the tooth. A tooth’s visible portion is the “clinical crown,” which can appear short even if the full, natural tooth structure, the “anatomical crown,” is normal. This illusion of shortness often occurs when the gum line fails to recede properly during tooth development, a condition known as Altered Passive Eruption (APE).
In a fully erupted tooth, the gum margin rests near the cementoenamel junction (where the enamel meets the root). With APE, the gum tissue remains positioned too far down onto the enamel, covering a significant part of the anatomical crown. This leaves the teeth looking square or stubby.
Additionally, teeth can become shorter over time due to wear (attrition) from grinding or clenching. This wear causes the teeth and gums to slightly erupt further, which can also increase gum display.
Jawbone and Lip Movement Factors
The most complex reasons for a gummy smile involve the underlying bone structure and facial muscle movement. One significant skeletal factor is Vertical Maxillary Excess (VME), which is an overdevelopment or excessive vertical length of the upper jawbone (maxilla). This overgrowth positions the upper teeth and supporting bone lower down in the face than they should be.
When the upper jaw is vertically too long, the gum line is carried downward, resulting in gum tissue display even with a normal lip length. VME is often a developmental or genetic factor that can give the lower third of the face an elongated appearance. Conversely, the soft tissues themselves can be the primary factor, even if the jawbone and teeth are correctly positioned.
A short or hypermobile upper lip can also cause excessive display. A hypermobile lip, sometimes called a hyperactive lip, results from the overactivity of the muscles that elevate the lip when smiling. These muscles, such as the levator labii superioris, pull the lip upward more than usual, exposing an excessive amount of gum tissue. A short upper lip, defined as less than the average adult length of 20 to 22 millimeters, also naturally uncovers more gum tissue when smiling, regardless of muscle activity.
Determining the Underlying Cause
Identifying the cause of excessive gingival display is paramount, as the appropriate treatment is dictated by the underlying biology. The diagnostic process begins with a thorough clinical assessment, including measuring the amount of gum tissue shown during a resting and a full, dynamic smile. The length of the upper lip is also measured, typically from the base of the nose to the lower border of the lip.
A dental professional measures the visible length of the teeth, the depth of the gum pocket, and the distance to the underlying bone. This bone sounding helps differentiate between excess soft tissue and a structural issue like Altered Passive Eruption. Dental radiographs (X-rays) are used to assess the position of the bone supporting the teeth and confirm the location of the cementoenamel junction (CEJ). For complex cases involving jaw structure, a specialized X-ray called a cephalometric analysis may be performed to diagnose Vertical Maxillary Excess by evaluating the skeletal proportions of the face.