Only your dentist can tell for sure whether you have tooth decay. That's because decay occurs below the tooth's surface, where you can't see it. When you eat foods that contain carbohydrates (sugars and starches), the carbohydrates leftover on teeth are eaten by germs, producing acids that eat into the tooth. Over time, the tooth enamel begins to break down beneath the surface while the surface remains intact. When enough of the sub-surface enamel is eaten away, the surface collapses, leading to tooth decay.

Decay around the edges, or margins, of fillings is also common to older adults. Because many older adults lacked benefits of modern preventive dental care when they were growing up, they often have a number of dental fillings. Over the years, these fillings may weaken and tend to fracture and leak around the edges. Germs accumulate in these tiny crevices causing acid to build up which leads to decay.