A smile that shows more than what is considered typical gum tissue is a common aesthetic concern known in dentistry as excessive gingival display (EGD), or more informally, a “gummy smile.” While a minimal amount of gum exposure, around 1 to 2 millimeters, is generally considered normal and even youthful, exposure exceeding 3 to 4 millimeters is often perceived as excessive. This phenomenon is not usually a health issue but is a result of various underlying anatomical and developmental factors. The appearance of an excessive gum line is determined by the interplay between the underlying jawbone, the mobility of the lips, the amount of gum tissue, and the size of the teeth themselves.
How Bone Structure Affects Gum Visibility
The foundational structure of the upper jaw, or maxilla, can be the primary reason for a prominent gum line, a condition referred to as Maxillary Vertical Excess (MVE). MVE occurs when the maxilla grows too long in the vertical dimension, causing the entire dental arch and the surrounding gum tissue to be positioned lower in the face than is typical. This skeletal overgrowth can result in a disproportionate appearance of the lower face.
When a person with MVE smiles, the excessive vertical height of the bone ensures that a large band of gum tissue is displayed beneath the upper lip. Diagnosis of this skeletal issue frequently requires specialized imaging, such as a cephalometric analysis, to measure the exact dimensions of the jawbone. For severe cases, correcting MVE often involves orthognathic surgery to surgically reposition the maxilla upward, reducing its vertical height.
The Role of Lip Movement
In some individuals, the amount of gum visible is not related to the jawbone size but instead to the dynamic movement of the upper lip during expression. This is known as a hypermobile upper lip, which means the muscles responsible for lifting the lip contract with excessive force. The average upper lip moves approximately 6 to 8 millimeters from its resting position to a full smile.
For a person with a hypermobile lip, the muscle contraction pulls the upper lip significantly higher than this average range, exposing an excessive amount of the underlying gum tissue. The specific muscle often implicated in this condition is the levator labii superioris alaeque nasi, which raises the center of the lip. This muscular hyperactivity can be temporarily managed with targeted injections that reduce the muscle’s strength, limiting the upward travel of the lip during a smile.
Excessive Gum Tissue
Another distinct cause for a gummy smile lies within the gingiva, or gum tissue, itself, particularly related to how it settles around the teeth. A common scenario is Altered Passive Eruption (APE), a developmental condition where the gum tissue fails to fully recede to its appropriate position after the teeth have finished their active eruption phase. Normally, the gum line stabilizes near the junction where the tooth enamel meets the root.
With APE, the gum margin remains positioned too far down on the tooth enamel, making the teeth appear shorter than they actually are, a state referred to as short clinical crowns. This results in the appearance of too much gum tissue covering the tooth surface.
A separate issue is Gingival Hyperplasia, which is an actual overgrowth or enlargement of the gum tissue. This condition can be a side effect of certain systemic factors, including some medications such as anti-seizure drugs, calcium channel blockers, or immunosuppressant agents.
Tooth Size and Shape
The visual prominence of the gums can also be an illusion created by the dimensions of the teeth themselves, even if the bone and gum tissue are otherwise normal. If the teeth are naturally smaller than average, a condition called microdontia, the overall proportion of the smile is skewed.
Similarly, excessive wear of the teeth, known as attrition, over time can reduce the height of the tooth crown. This shortening can be caused by habits like teeth grinding or simply from aging.
For optimal aesthetics, the width-to-length ratio of the central upper teeth should typically fall within a range of approximately 75 to 85 percent.