DEAR DOCTOR K:
What is tooth decay, and how does it happen?
Tooth decay is a disease of the mouth that can lead to cavities and infection. But before we start talking about sick teeth, let’s talk about healthy teeth.
Each tooth has one or more roots that are anchored in the bones of the jaw. Since those roots are inside the jaw bone, they are invisible. The part of the tooth that we see, sticking out above the gumline, is the crown.
The crown of the tooth is covered with a hard, whitish material called enamel. The enamel ends at about your gumline, where the root begins. The root of the tooth is covered with a thin layer of another hard, bonelike material called cementum.
Inside the tooth are two other types of dental tissue: dentin and pulp. Dentin is harder than cementum but softer than enamel. Most of the tooth is dentin, so it is primarily the hard dentin that is doing the work of chewing your food into tiny pieces.
The core of a tooth is a chamber extending from the crown into the roots. Inside this chamber is the pulp, a collection of loose connective tissue laced with blood vessels. A network of nerves runs through the pulp. When the pulp is damaged or infected, the nerves coursing through the pulp make the tooth hurt.
Tooth decay (also known as dental caries) begins with the development of plaque, the sticky, bacteria-laden film that collects on your teeth between brushings. The bacteria in the plaque “eat” sugar and food that stays in the mouth after eating. When they do that, they give off acid as a waste product. This acid dissolves the outer enamel surfaces of the teeth, causing tiny pits to form.
The earliest stage of decay appears as a white or brown area on a tooth. You can’t see this white spot, but your dentist can. If decay is caught at this stage, there’s a good chance it can be stopped and reversed. Treatments include limiting sugary snacks and beverages and taking fluoride supplements. Your dentist can also apply fluoride, an antiseptic or a sealant to your teeth to stop the progress of early decay.
Unchecked, bacterial acid will bore a hole in the enamel. This is a cavity. At this point, the tooth may ache. It may also be sensitive to hot, cold or sweet foods.
Without treatment, the cavity gets bigger, extending into the soft tissue of the pulp and causing an infection called pulpitis. The infected pulp tissue swells, squeezing neighboring blood vessels. This cuts off the blood supply to the pulp, and the pulp dies. People with pulpitis usually feel severe pain. (I’ve put an illustration of this process at the end of this post.)
I shouldn’t need to tell you how to prevent tooth decay, but I will anyway: Brush and floss every day, and minimize sugary snacks and beverages.
The ravages of tooth decay
Tooth decay usually gets worse gradually. When left untreated, it can have devastating effects. Decay begins with the development of plaque, which contains bacteria. These bacteria can dissolve the enamel of the tooth, boring a hole known as a cavity (A). At this point the damage is limited to the enamel and dentin. But as decay continues, the damage can extend to the pulp. The pulp becomes infected and inflamed. This is known as pulpitis (B). The swelling resulting from inflammation can cut off the blood supply, causing the pulp to die. The infection can spread to the root canals and can reach beyond the tip of the root, resulting in an abscess (C). An abscess can be quite painful. If the infection enters the bloodstream, the problem can become life-threatening.