Excessive gum exposure, commonly known as a "gummy smile," is a condition characterized by an overly visible gum line when smiling. The most frequent cause of a so-called gummy smile is hyperactivity of the upper lip muscles. Other factors include a disproportionate size between the teeth and gums, with some individuals having small teeth or overly prominent gums that overshadow the teeth. The aesthetics of a smile are subjective; however, gums are generally considered prominent if 4 millimeters or more are visible above the lip line when smiling.
The upper jaw and upper lip also contribute to gum visibility, often resulting from a combination of factors. These may include the size and shape of the teeth, the degree of upper lip movement, the surface area of visible gums, and the positioning of the upper jaw and teeth in relation to the skull.