Between the gum and tooth there is a small groove, called sulcus. When calculus (tartar) is left on the tooth, the microorganisms inside it irritate and inflame the gums, causing them to bleed. This is an early stage of gum disease called gingivitis. When left untreated, gingivitis can lead to deeper sulcus or pockets, allowing more tartar to collect. This eventually causes the gum and bone structures around the tooth to break down leading to irreversible damage, tooth mobility and loss.
The good news is if the gum disease is caught in time, it can be improved and further bone damage of the teeth can be prevented through periodontal therapy, or deep cleaning. Unlike routine dental cleaning, where dental plaque is removed from the tooth above the gumline, deep cleaning also involves cleaning, scraping, and smoothing the root surface of the tooth so that the gum can reattach to the tooth and reduce the size of pockets.