Thursday, November 21, 2013

Metal Filling-Induced Cracks in Enamel

While tooth enamel is normally hard and brittle, over time very small microcracks will appear in the enamel. This is thought to be due to the thermocycling of the enamel from items you eat and drink that are hotter or colder than room temperature. Again, over time, the expansion and contraction of the enamel causes the cracks to appear. This is not considered a dental problem and is not usually treated. However, teeth that are restored with metal fillings are a different story. Silver amalgam (metal) fillings are composed of not only silver, but also other metals, too. One of the metals is mercury. Most filling materials are at least 30% and some are as high as 50% mercury. Besides being classified as a heavy metal, mercury is a liquid at room temperature (although it is not a liquid in the filling material) and rapidly expands and contracts when its temperature is raised and lowered.

How Cracks Occur
Metal fillings can cause cracks in tooth enamel.
Your mouth is at a temperature of about 98.6 degrees. When you drink hot coffee, followed by eating cold ice cream, the temperature of your mouth will rapidly cycle up 20 or 30 degrees, then down 60 or 70 degrees, then back up to 98.6 degrees. This happens every time you eat or drink something that is not the same temperature as your mouth. Because of the expansion of the mercury component and other metals of the filling material, this expansion and contraction of the filling will cause an outward pressure on the enamel and dentin. The larger the filling is in the beginning and the thinner the enamel is, the more prone the tooth will be to developing cracks. Cracks also provide an avenue for the ingress of fluids and bacteria, a pathway for a cavity to start deep in the tooth. If this were not bad enough, the metal will absorb some of the moisture present in your mouth, and as time passes, will increase in volume. As it expands, it will put outward pressure on the walls of the original filling preparation. This also promotes development of cracks in the tooth.

There are two different paths by which the metal filling can break teeth. You can see for yourself that the fillings are changing. The once smooth and shiny metal becomes black, dull, pitted, and rough. There is metal fatigue. The older the filling, the more likely this has happened. You may also have some tooth sensitivity from fluids or sweets. This is an additional indication that the filling may be leaking and failing. If the filled tooth hurts when you bite down, the tooth may be split and nerve damage may have occurred, or it may be a different, more serious problem altogether. Directly placed metal fillings are an antiquated technique with a material that has been essentially unchanged for almost 180 years.

Treatment Options
You have a choice. You can wait until the cracks become serious and painful and then do even more extensive restorative work, or you can begin, right away, to replace the metal fillings where the cracks are evident. Sometimes, cracks do not get bigger or cause problems; however, many cracks do. During the years, the metal fatigues more and more, and the crack enlarges. In most cases a tooth-colored, bonded direct resin can be used to replace the metal. It seals better to your tooth and has not shown that it cracks the teeth as the metal fillings do. If the existing crack or filling is moderate to large, a gold, resin, or ceramic inlay/onlay will be recommended for the replacement material.


If you have any questions about metal filling-induced cracks in enamel, please feel free to ask us at (512)250-5012. – Omni Dental Group


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