How Fillings Work
The treatment of dental cavities goes back centuries, but it was not until 1875 that Dr. G.V. Black first described an organized approach to their treatment. His systematic methods are still used today, primarily for the placement of silver (amalgam) fillings. Dr. Black advocated removing the decayed part of the tooth, and extending the tooth preparation to include certain grooves and other 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 is able to be probed with an explorer, it has undergone cavitation, and requires treatment. Early dental cavities that have not spread to the dentin or have undergone cavitation should not be treated, as they can be healed or re-mineralized with fluoride.
The goal of treating cavities involves two basic principals: removing the decayed portion of the tooth, and rebuilding the missing tooth structure with a filling material. The dentist usually begins the procedure with an injection of local anesthetic (xylocaine in most cases). The tooth is isolated from the rest of the mouth, and in most cases, a high-speed dental drill is needed to remove the decay and prepare the tooth for the filling. Depending on which material is used, the dentist will vary the tooth preparation accordingly. After the tooth has been prepared, a liner is often used to reduce tooth sensitivity. Common liners include gluma, copalite varnish and dycal. Dycal is a compound containing calcium hydroxide, and is used in deep cavities to stimulate the dentin to regenerate and protect the dental pulp. In deeper fillings, a base is used in addition to the liner. Common bases used under dental fillings are glass ionomer cement, and zinc phosphate cement. The main purpose of the base is to insulate the tooth from temperature changes in the mouth. The dentist and patient can then choose a number of different materials to fill the tooth, but the most common are silver (amalgam), white (resin), porcelain, or gold. These materials are layered on top of the liner or base to finish the process of rebuilding the tooth.
After a tooth has been filled, it is not unusual for the tooth to be sensitive for a day or two. In general, the deeper the filling, the more likely the tooth will have prolonged sensitivity, especially to cold food or beverages. Most fillings should be completely comfortable within two weeks. In some cases, the filling will be built up too high, and a second appointment is needed to shave down the filling to a comfortable level. If sensitivity lasts more than two weeks, it may indicate that there is a void under the filling. Prolonged discomfort may also indicate a tooth that has an infected pulp, and requires root canal therapy.