There are many facets to a beautiful smile. As expected, the main components are going to be your teeth and gums. The condition of your teeth is certainly a factor, and your gums play a very important role in stability and protection of your teeth, however, they also serve an aesthetic purpose as well.
With that aesthetic, proportion becomes the deciding factor in what exactly a gummy smile is. Typically if a smile displays more than 4 mm of gum tissue, it would be considered a gummy smile. There are a few issues that can cause this.
Excessive gum tissue.
With cases of this, there is too much gum covering the tooth crown. This can be corrected by doing a procedure called crown lengthening. This procedure can remove some of the excessive tissue affectively showing more tooth length.
Teeth appearing too short.
In cases of this, the problem is not necessarily with the gums, however it could appear that your teeth are “too short“ Some causes of this are worn down teeth that come with aging, teeth grinding, or if a tooth did not fully erupt. A solution to this is to make the teeth appear longer with veneers, crowns, or other special techniques.
Upper lip movement.
In instances of this, it is not your gums, or your teeth being out of proportion, but rather your upper lip could be rising up too high when you smile. This is a condition called hypermobility. A temporary solution to this would be to use Botox injections that would prevent the muscles in the lip from overextending. A more permanent solution could be found through periodontal surgery with a lip stabilization that would correct movement in the upper lip.
In this situation your gums would appear more prominent if the upper jaw extends forward and too far down. This is where orthognathic surgery could be applied to straighten the jaw. This is done by repositioning the drawer relative to how it is connected to the skull. Through this re-positioning, the drawer would be set up and back and would effectively reduce prominent gums when smiling.
These various procedures show a large range of different techniques from cosmetic to surgical treatments. A full dental exam is recommended to be able to determine which if any of the listed treatments could help reduce a gummy smile.