There are 2 main forms of gum disease: gingivitis and periodontal disease. Gingivitis is seen as reddening, sore, swollen, bleeding gums, and is a reversible process with better tooth brushing.
If left untreated, periodontal disease begins, where the bony support for the teeth roots is lost – this is an irreversible process, usually resulting in gum abscesses and tooth loss.
Gum disease is caused by the bacteria in the plaque on your teeth, and to prevent it, you need to make sure to remove all the plaque from your teeth twice daily.
Many of the bacteria in plaque are harmless to the gums, but over the course of a few days, the bacteria changes to more harmful types which release enzymes to irritate the gums and bone around the roots of the teeth.
Besides brushing twice daily, most people should also floss once a day to clean between the teeth or use interdental brushes to clean where the spaces between the teeth are larger. The dentist will advise you and show you how to use these.