What Causes Dental Fillings to Hurt?

Updated November 21, 2016

Dental fillings are restorative procedures a dentist applies as the result of tooth decay. The dentist removes a decayed a portion of the tooth and replaces it with another material, usually metal or composite resin. Most dental fillings live long, happy lives without causing problems for the person wearing them. However, occasionally fillings become sensitive and start to hurt. Several things can cause pain in fillings.

Decay and Restorations

A dentist diagnoses decay in two ways: with diagnostic X-rays and by probing suspected decay areas with an instrument called an explorer. The explorer is a sharp pigtail-shaped tool used to check even the smallest pit or fissure of a tooth for decay. Normal enamel and dentine are hard and a dentist cannot penetrate it with an explorer. If the dentist finds decay, the explorer will go directly into it, and it will be difficult to pull it back out because decay is soft and sticky. Decays show up on an X-ray as a dark shadow in the tooth. Usually even decay under an old filling will eventually show up on X-rays. The materials commonly used for fillings are amalgam, a silver alloy with mercury or composite resin, that can be acrylic or glass-based.

Filling or Restoration Preparation

When a dentist repairs a newly decayed tooth or removes an old filling, he makes a box or "cavity prep" with a high speed dental drill. A slow-speed drill and a spoon excavator remove the decay. He medicates the floor of the cavity prep closest to the nerve with a material that will help dentine regenerate, and lines the entire cavity prep with insulating varnish. Once she has placed the filling material, adjusted the bite and smoothed the edges, the patient is ready to go home with a warning that the tooth may be sensitive for a while after the procedure.

Reasons for New Dental Fillings to Hurt

Some sensitivity is normal and expected after a new filling. Decay can irritate the nerve of the tooth, especially if the decay is deep, causing it to be more sensitive than usual because of the new silver or composite in the tooth. Discomfort with thermal changes, especially to cold, are common. Occasionally the tooth hurts when chewing with the new filling. This may be because an area of the filling is too "high," causing that area to be the first part of the tooth that comes together with the opposing tooth when chewing. The tissue around the tooth also may be sensitive because of the injection used to anaesthetise the tooth or from the area being worked on in general. Another sensitivity connected to amalgam fillings is similar to an electric shock. It is called "galvanism" and happens when the new filling reacts to other metals, such as a fork, when eating. Usually, once the amalgam oxidises it is no longer a problem.

Sensitivity in Existing Fillings

Fillings were not meant to last forever. However, silver and composite fillings can last that long with proper dental care. In some cases, a filling starts to get sensitive or starts to hurt. Often the most common cause is that the filling has cracked or fractured under the stress of chewing. When a dentist removes decay from a tooth, it is difficult to get every single piece of bacteria. Sometimes decay will recur because tooth bacteria is anaerobic, meaning it does not need air to survive and grow. Because of the filling's proximity to the nerve of the tooth, occasionally decay penetrates the nerve chamber, causing the death of the tooth. In this case, the tooth can not be repaired with another filling. You will need a root canal and perhaps a crown to restore it. A filled tooth can be sensitive to hot, cold and sweets, not necessarily because anything is wrong with the filling, but because the gum line of the tooth has receded, exposing the more sensitive portion of the tooth called "cementum." A filling can also hurt when the remaining tooth structure fractures or breaks off. Report all of these symptoms to your dentist for diagnosis and care as soon as possible.

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