In some people, there is a weakness between where the tooth meets the gum. In health, the gums are pink and firm with no pain and no bleeding. With gum disease the bacteria in plaque gather at the junction between the tooth and gum. The body’s immune response attempts to remove the invading bacteria by swelling and attacking the germs. As the gums become more inflamed, they bleed more easily, allowing more germs to invade into the space. When a gap opens up between the gum and the tooth the disease progresses and the bacteria are able to hide in this gap, away from the toothbrush. This gap is known as a pocket. Dentists can measure the pocket depth to assess how far advanced the disease is and whether it is progressing or stable. Xrays also play a key role in measuring how much bone has become lost in the breakdown of the gums. Once bone is lost around the tooth, it does not grow back.