This case highlights the role of bacteria in in disease. Bacteria will adapt to their environment individually. However, collectively, the type of bacteria that make up an infection will change as the environment changes. The bacteria colony on the tooth surface, exposed to the person’s breathing (aerobic bacteria) and fed by sugars will cause damage to the tooth surface. These bacteria will convert sugars to lactic acid, making the tooth enamel porous. Then the enamel structure eventually collapses to form a defect exposing the bacteria to the layer underneath, the dentine. Bacterial love dentine and the defect. The dentine they feed on, and the defect they can hide in from the immune protects in the saliva and the fluid released by the gum at the neck on the tooth.

This person’s filling was leaking, but was not apparent on the xray. If there is fast movement of decay, it can take a while before the decay makes the tooth stucture dissolve and wash out of the tooth. So a hiding environment, say under a filling or in a thin crack, and with the right diet and lack of, or difficulty of cleaning, and the bacteria won’t hold back. 

But there’s more!

The bacteria “soup” environment is changing itself. The oxygen content is falling as decay travels further away from the breathing environment of the person. In comes the oxygen hateing (anaerobic) bacteria. They can be very aggressive and evade the immune system.  As the bacteria works it way down the root canal, it then causes the pulp  tissue (nerve and blood supply) to become necrotic (die). There is no back up blood supply and now the body can no longer bring its immune system inside the tooth. 

Onwards the bacteria go, being fed from oustside the tooth and inside the tooth and now it enters the bone. The body is now trying to attack the bacteria and prevent it spreading in the body. If the bacteria is aggressive, or the immune response is weak, pus may occur. Pus is the destruction of tissue and is a mixutre of necrotic tissue, bacteria and immune cells. Not good!