What Are the Advantages and Disadvantages of Composite (white) Fillings?

Many people ask us why we do all of our fillings on back teeth using composite (white) fillings rather than silver amalgam. This is a bit of a controversy in dentistry right now, and hopefully this newsletter will enlighten patients on this issue.

Silver amalgam is composed of silver, copper, tin, zinc and mercury. The mercury is what allows the formulation to be in a putty-like consistency while it is placed in the tooth, and then harden to a metal consistency. Amalgam has been the filling of choice for about a century. It's advantages include: strength, durability, low cost, and ease of placement.

An amalgam can be contaminated by saliva or blood during placement, and it's longevity will not be affected. Amalgam's disadvantages include: undesirable esthetics (they start out silver/gray and end up black with age), lack of bonding, frequency of tooth fracture, and some concern about mercury toxicity (although this has never been proven scientifically).

Composite fillings are very different from amalgams in many respects. They are made from a plastic resin with varying amounts of glass fillers, depending on the brand. Composites have been in use since the 1960's, but were initially used only for front teeth. What sets composites apart from amalgam is that: 1-They are tooth colored. 2-They are bonded to the tooth. This is the most important feature of composite fillings, and the one that has caused such a revolution in dentistry. The composite is microscopically attached (bonded) to the tooth by a 3 step process. First, the tooth is treated for 15 seconds with a mild acid. This conditions or "etches" the tooth. It provides microscopic irregularities in the enamel, and opens small tubules in the dentin of the tooth. The second step is the placement of a bonding agent. This is a very thin type of composite that flows into the enamel irregularities and dentinal tubules. It is then cured (hardened) with a very bright blue curing light. This very thin initial layer is now microscopically locked into the surface of the tooth. The third step is the addition of a chemically similar composite filling material that then chemically bonds to the first layer. This produces a filling that is actually bonded to the tooth, instead of being simply placed in the tooth like you would pour cement into a post hole.

The two most important features of the composites are a direct result of the fact that composites are bonded to the tooth. First, they allow more conservative restorations on the tooth. Because an amalgam is held in by undercuts in the cavity preparation, you have to drill out more than just the cavity to get an amalgam to stay in place. Healthy tooth is removed to provide retention for the filling. A composite, on the other hand, because it bonds to the tooth, can be placed in a very small hole, with no retention, and stay in. We only need to remove the decay in your tooth to place a composite filling. The second great feature is that composites restore the tooth back to it's original strength. Amalgams act like a wedge between the cusps of teeth, and we see a lot of tooth fractures related to large amalgam fillings. Composites bond the tooth together, and restore it's strength. A force of approximately 18 mPa is required to break teeth. The latest generation of bonding agents bond to the tooth with a strength of 28-56 mPa! They stick to teeth better than teeth stick to themselves! And of course, composites look like teeth! Who wants a silver/black filling, when they can have a white one?

So, if composites are so great, why do most dentists still do amalgams on back teeth and not composites? There are a variety of reasons for this, but the biggest reason is that they are too technique sensitive. Composites must be kept absolutely dry during placement, or they will not bond. You must follow the manufacturer's instructions for bonding to the letter, or they will not bond. Composites are also very time consuming. You can do an acceptable amalgam on a tooth in, for instance, 30 minutes. To use composite will probably take 45-60 minutes. There are also a variety of specialized instruments that are necessary to do composites properly on back teeth. Because of the additional time needed to place them, the specialized instruments, and the fact that composite materials are very expensive, composite fillings cost more than amalgams. The question is, are they worth it? We believe that the answer to that is a resounding YES!

When properly done, composites will last as long as amalgam, they look just like a natural tooth, and they strengthen, rather than weaken the tooth. Technology for bonding is constantly evolving, and what we use today is light years ahead of what was in use even two years ago. The nationally known dentists who are on the cutting edge of restorative dentistry have pretty much abandoned amalgam, as we have. Just as computers are better than slide rules, we feel that the technology of bonded composites is much preferred over amalgams.
 

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