Tooth decay is caused by a process that occurs over time. Here’s how tooth decay develops:

• Plaque forms. Dental plaque is a clear, sticky layer that coats your teeth. It’s caused by eating a lot of sugar and starches and not brushing your teeth properly. When sugars and starches aren’t removed from your teeth, bacteria quickly start to feed on them and form plaque. Plaque that remains on your teeth can harden below or above your gum line into tartar. Tartar makes plaque harder to remove and creates a shield for bacteria.
• Plaque attacks. Acids in plaque remove minerals from the hard outer enamel of your tooth. This erosion causes small holes or pits in the enamel—the first stage of tooth decay. Once the enamel wears away, bacteria and acid can reach the next layer of your teeth, called dentin. This layer is softer than enamel and less resistant to acid. Dentin has tiny tubes that communicate directly with the nerve of the tooth, causing sensitivity.
• The destruction goes on. As cavities develop, bacteria and acid continue their journey through your teeth, moving to the inner tooth material (pulp), which contains nerves and blood vessels. The pulp becomes swollen and irritated by the bacteria. Because there is no room for the swelling to expand inside the tooth, the nerve gets compressed, causing pain. The discomfort can even extend beyond the root of the tooth to the bone.

Treatment for tooth decay depends on the stage of the decay and the extent of damage to the tooth. It involves a variety of approaches, from non-invasive methods in the early stages to more complex interventions in advanced cases. Here’s how treatment works:

• Fluoride treatment. If your decay has just started, fluoride treatment can help repair tooth enamel and can sometimes reverse decay in its very early stages. Professional fluoride treatments contain more fluoride than what is found in tap water, toothpaste, and mouthwash. Fluoride treatments can be a liquid, gel, foam, or varnish that is applied to your teeth or placed in a small tray that fits over your teeth.
• Fillings. Fillings, also called restorations, are the main treatment option when decay has progressed beyond the earliest stages. Fillings are made from a variety of materials, such as tooth-colored composite resins, porcelain, or dental amalgam, which is a combination of several materials.
• Crowns. For extensive decay or weakened teeth, you may need a crown — a specially fitted covering that replaces the entire natural crown of your tooth. Your dentist drills through the entire decayed area and enough of the rest of your tooth to ensure a good fit. Crowns can be made from gold, high-strength porcelain, resin, porcelain fused to metal, or other materials.
• Root canals. When decay reaches the inner material of your tooth (pulp), you may need a root canal. This is a treatment to repair and save a severely damaged or infected tooth, rather than removing it. The diseased pulp of the tooth is removed. Sometimes medicine is placed in the root canal to clear the infection. The pulp is then replaced with a filling.
• Tooth extractions. Some teeth become so badly decayed that they cannot be restored and must be removed. Removing a tooth can leave a gap that allows your other teeth to shift. If possible, consider getting a bridge or dental implant to replace the missing tooth.