The periodontium includes the supporting bone and soft tissues that keeps a tooth in its position. When the gums are not cleaned routinely a layer of plaque and calculus starts to cover the tooth structure and leads to inflammation, redness and bleeding of the gums. This condition is called gingivitis and it is easily treatable with simple scaling (removal of the plaque and calculus), which can be done by your dentist/ hygienist.
Periodontitis is a chronic condition apparent in about 20 % of the population, where your body tries to fight the bacteria gathered around the tooth and gum but in the process the supporting bone is being broken down and can lead to loss of bone and teeth. The gum starts to detach away from the tooth, forming a pocket, in which plaque can gather. This is an irreversible process and it is not curable but the disease can be well controlled and the progress of it slowed down by regular deep cleaning of your teeth and gums.