After doing porcelain gum black (gray) reasons: 1, metal porcelain crowns formed during the production process of metal oxides, metal ions gradually precipitated in the intraoral environment, into the gingival tissue, resulting in the latter discoloration; 2, compared with the normal living pulp teeth, dead pulp teeth (teeth that have killed the dental nerve) will darken, darken, if the root surface covered by gum tissue thin, may be transparent to the color of the root below it. For the above-mentioned reasons of gum color darkening, the following methods can be used to improve: 1. Use all-porcelain crowns to eliminate the production of metal oxides and the precipitation of ions; 2. Use membrane gingival surgery to thicken the thickness of the gingival tissue on the surface of the discolored tooth root to prevent the color of the root from coming through.