This is the periodontal disease that we have been talking about. Plaque builds up and hardens under the gums and they in turn, pull away from the teeth, forming pockets of infection. This infection leads to the loss of bone that holds the tooth in its socket, then to tooth loss. It can not be treated by regular brushing and flossing. You are, at this point, in the dental chair of a periodontist, a dentist who specializes in treating gum diseases.
Treatment depends on how much damage has been done.
In the early stages, the dentist can deep clean the gums to remove hardened plaque and infected tissue under the gum. The dentist will smooth the damaged root surfaces of the teeth. This allows the gum to re-attach to the teeth. Antibiotics and mouthwash are often prescribed to control the infection. Gum surgery is necessary when the disease has advanced to the point where the tissues that hold the tooth have been destroyed.