A gummy smile is characterised by a person showing too much gum when they smile. This is usually caused because their teeth and gums are out of proportion. It could be that either their teeth are too small or the gum is too prominent for the teeth to make an impact.
The appeal of a smile is a matter of perception. However, a smile is generally considered gummy when four millimetres or more of gum tissue shows beyond the lips.
The upper jaw and upper lip also play a role in gumminess, and it is often a combination of factors that lead to an overall gummy smile. These factors include the size and shape of the teeth, the degree of movement in the upper lip, the amount of gum tissue displayed and the position of the upper jaw and teeth in relation to the skull.