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Amalgam’s properties–the reason it has been so successful

amalgams

Silver amalgam’s main disadvantage is its appearance in the teeth. It tends to be gray or black, or sometimes silver if the patient brushes regularly with a toothpaste that contains an abrasive. Older forms of amalgam tended to corrode imparting a dark usually bluish stain to the teeth.  This stain could permeate the dentinal tubules and is very difficult to remove when replacing the old filling.  The advantages to metallic fillings are that they are incredibly durable, not likely to break, and last a LONG time. Five to ten years is the average, however, in a very clean mouth not exposed to too much sugar, twenty years is not an uncommon lifespan for a well done amalgam. It is not very technique sensitive, which means that the skill of the dentist is less important to the wear of an amalgam than it is with the other types of restorations.

Amalgam tends to be self sealing which means that once it is placed, a small amount of corrosion takes place underneath the filling and this corrosion fills microscopic voids between the tooth and the filling. Moreover, this corrosion is water resistant and once in place prevents further corrosion and the entry of fluids containing sugar and bacteria which are the agents that cause more decay. This self sealing property is unique to amalgam, and is one of the main reasons why amalgam fillings resist recurrent decay better than the older, more expensive cast gold restorations.  They are also more reliable than composite posterior fillings in resisting recurrent decay, especially in patients who use a lot of sugar.  Finally, they are less expensive than gold or composite restorations because they take less time to place.

Resin Composite fillings (sometimes called “porcelain” fillings)

Having sung the praises of Amalgam restorations, I will now state flatly that I have given them up in my own practice in favor of the new generation of composite restoration. The reasons follow my description of composite filling materials.

Before2

After2

The glass particles give the composite restoration their color (and their stiffness in the unset state). The acrylic is the plastic matrix that holds the glass particles together. Most composite restorations today are “light cured” which means that the acrylic remains fluid until a very bright light is shined on it causing it to harden. Light curing allows the dentist time to work with the material, building and shaping it correctly, and when ready, to harden it immediately with the light. The light curing also makes for a more color stable restoration. The new tooth colored composite restorations do not get yellow or brown with age as the older ones did.

compositefilling

The Before and after images of the tooth above are impressive, but do not tell the whole story. In fact, a tooth that is built in more than 50% restorative material is inherently weak and should be prepared for a crown. This does not mean that all badly damaged teeth should be crowned immediately. In fact the decay in this one was quite deep. Deep decay places the nerve in jeopardy, so a plain filling may serve as a good intermediate restoration to test whether the nerve will die before a final crown is placed on the tooth. For the full story, click here.

The porcelain particles also give the restoration a great deal of resistance to wear. Amalgam fillings will probably always wear less than composite restorations, however the recent advances in particle formulation and shape have made the newest posterior composites quite competitive for filling back teeth. Five to seven years is average. Composites are even stronger than amalgams in shear strength which makes them better for overlaying large biting areas.

Composite fillings have been used in front teeth for years, but only recently has the technology in composite formulation improved enough to allow their common use in back teeth. Prior to acrylic/glass composites, other types of composites were used in areas where aesthetics was important. This is why even in the early twentieth century people were not forced to have silver amalgam fillings in their front teeth. However, even in the 1980’s the technology had not yet advanced enough to allow the routine use of composite to restore chewing areas of the back teeth.

Meth mouth— What happens to your teeth when you are a serious addict? Click on the icon below to find out

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Composite resins are still not as popular with dentists for repairing back teeth as old-fashioned amalgam.  In fact, only about 25% of dentists currently use them routinely for restoring posterior teeth.  The reasons for this are that they are not as wear resistant as amalgam restorations, they are more technique sensitive than amalgam, and there is a tendency for more prolonged tooth sensitivity to cold after the restoration is done.  On the other hand, as the materials continue to improve, they have become tougher and more wear resistant while improvements  in placement technique have reduced cold sensitivity.   However, the greater difficulty in placing these restorations remains a deterrent for many dentists, and continues to keep the cost of the service higher than for an a comparable amalgam restoration.

For those interested in the more technical aspects of composites and dental cements please click here to visit my eleven page course on dental materials.  Here I discuss the different types of composites and cements, their formulations and their uses.

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