"You may have asked your periodontist about procedures to improve a "gummy" smile because your teeth appear short. Your teeth may actually be the proper lengths, but they're covered with too much gum tissue. To correct this, your periodontist performs a dental crown lengthening procedure.
During the dental crown lengthening procedure, excess gum and bone tissue is reshaped to expose more of the natural tooth. This can be done to one tooth, to even your gum line, or to several teeth to expose a natural, broad smile.
Your dentist or periodontist may also recommend dental crown lengthening to make a restorative or cosmetic dental procedure possible. Perhaps your tooth is decayed, broken below the gum line, or has insufficient tooth structure for a restoration, such as a crown or bridge. Crown lengthening adjusts the gum and bone level to expose more of the tooth so it can be restored."1
1."What Is a Periodontist?"Http://www.perio.org. American Academy of Periodontology, 24 Feb. 2011. Web. 11 Apr. 2012.