Plaque and tooth decay
Plaque, unless removed by thorough brushing and flossing, leads to decay. The bacterial activity occurring in plaque produces an acid by-product which, ultimately erodes the tough tooth enamel.
Tiny areas of decay, or caries, develop. It is harder to clean and remove plaque from these spots, therefore the acidic erosion continues. There is typically no pain in this stage.
Over time the caries deepen, until the enamel is penetrated and the softer, sensitive dentin is attacked. There are two important characteristics of this stage: early pain, and the more rapid erosion of this softer tissue.
Without treatment, the inner chamber of the tooth is finally reached, and most significantly, the pulp or nerve within. Nerves, highly sensitive structures, designed to alert us to problems in the body, become inflamed resulting in severe pain. It is likely that more complex treatment will be required to relieve this level of pain.