Dental cavities, also known as carries, have been around for thousands of years. However, the problem has been steadily increasing over time. For example, scientists have discovered fossilized remains of men and women from the Iron Age in @Warwickshire, @England. These remains showed a cavity rate of only about 8 percent. When the scientists examined today's Warwickshire inhabitants, they found a remarkably high cavity rate of 48 percent. The culprit is most likely a modern diet, which consists, in large part, of highly processed, sugar-containing foods.
Dental cavities are caused by a combination of carbohydrate-containing foods and bacteria that normally live in our mouths. While there are many different types of bacteria, there are only a few that contribute to cavity formation. These bacteria reside in a film that continuously forms on and around our teeth. We call this film plaque. The bacteria use carbohydrates for food, producing acid in the process. The acid causes the @pH (a measure of acidity) on the tooth surface to drop. Before eating, the pH in the mouth is about 6.2 to 7.0, slightly more acidic than water. After eating sugary foods and other carbohydrates, the pH drops. At a pH of 5.2 to 5.5 or below, the acid begins to dissolve the hard enamel that forms the outer coating of the teeth. As the enamel wears away, a cavity results.
Cavities can spread beyond the surface enamel, invading the softer dentin located directly beneath. It can also move to the nerve and blood supply of the tooth contained within the pulp, leading to abscesses and infections.
Cavities can form on the biting surfaces of the back teeth -- the molars and premolars. In these locations they usually cause pits and grooves. These are thin areas of enamel that contain recesses. They can easily trap food and plaque. As the trapped bacteria continue to produce acid, the pits enlarge to form wider grooves and finally hole. Once worn through the enamel, they can invade the underlying dentin.
Cavities can also form on the front teeth, or on the back (lingual) areas of the teeth, where there is a smooth surface. In a smooth surface cavity, the acid must travel through the entire thickness of the enamel.
And as we get older, certain body change can themselves lead to tooth decay. For example, the gums can recede from the teeth, exposing the roots to plaque. The roots are covered with cementum, which is softer than enamel. This makes them more susceptible to decay, and the majority of people over age 50 have some form of tooth-root decay.
Also common in older people is decay around the edges of previous fillings. Over time these fillings can weaken, leading to cracks around the edges. Bacteria accumulate in these tiny, hard-to-reach cracks, promoting decay.
The treatment of dental cavities goes back centuries. But it was not until 1875 that @G.@V. Black, a dentist at @Northwestern University Dental School, first described an organized approach to their treatment. His methods are still used today. Dr. Black removed the parts of the teeth that were decayed. He then extended the tooth preparation to include not only the cavity, but also certain other grooves and surfaces. This process, "extension for prevention," is considered prudent because it provides the tooth with some protection from further decay in the future.
Most cavities discovered during a dental examination will need to be treated. In general, if a cavity has broken through the enamel and is into the underlying dentin, or if it is able to be penetrated with a dental instrument, requires treatment. Early dental cavities -- ones that have not spread to the dentin -- can simply be re-mineralized with fluoride or filled with amalgam. If the decay has spread further into the tooth structure, it can lead to gum disease. This needs to be treated more aggressively, with scaling and planing, flap surgery, or even a root canal.
