There is no effective cure for gum darkening caused by some primary diseases (e.g. Pulger’s disease, Addison’s disease, etc.). In contrast, for gum darkening caused by certain external factors, the gum darkening can usually be slowly restored to normal after treatment and removal of the external triggers, for example.
For gum darkening caused by chronic metal poisoning, removing the trigger that caused the chronic metal poisoning.
For dark gums caused by gingivitis or calculus, removal of plaque and calculus and treatment with medication etc.
For dark gums caused by long-term smoking, the smoking habit should be stopped, etc.