Amalgam vs. Composite: Filling in the Blanks

This is the second in a five-part series examining intellectual debate in dentistry. Part 1 can be found here. 

By Susan Richards

 

With much of a dentist’s time spent filling caries and preventing further damage to a tooth, it’s interesting to learn that the materials chosen for the task have a long history of strong opinions equal to their strength in bonding properties. The concerns and controversies surrounding amalgam versus composite fillings range from longevity and durability, to toxicity and patient safety, and have raised professional hackles for almost 200 years.

Some Facts About Fillings

Although the use of dental amalgam can be traced back as far as 659 A.D. during the Tang Dynasty, it was French physician Louis Regnart who is credited with adding one-tenth by weight of mercury to the metals, creating a temporarily softer, room-temperature alloy. Until then, patients had the unpleasant choice between tooth extraction or having molten gold or silver compounds poured into their carious teeth. (Ouch.) The amalgam was further improved upon a few years later and again in the 1890s, then 1959 and in 1963.

Metal fillings – usually silver in composition and color – have been widely used since then, with the American Dental Association (ADA) estimating more than 100 million placed each year in this country.

The composite filling was invented in the early 1960s as a significant improvement on the silicate and acrylic resins used at the time for esthetic dentistry. Since then, there have been many innovations on both the appearance and adhesion, as well as the longevity of the fillings.

Durability & Longevity

It goes without saying, that a large part of the fillings debate is one of a practical matter for both dentists and patients – how durable are they and how long will they last. Several factors can affect the longevity of any dental restoration, including the substance used, normal corrosion, or faulty placement.

For many years it was commonly accepted that amalgam fillings could be counted on to last the longest – recent studies have shown some high-copper amalgams performing well for 12 years and more. The main problems plaguing the life of the posterior, stress-bearing restorations are typically secondary caries and incidents of bulk and tooth fracture.

Before the 1990s, the lifespan of posterior composites was expected to be much lower than amalgams – from three to 10 years, and fewer than five for larger fillings. This was due to shrinkage and inadequate adhesion provided by the materials, however major improvements in filler technology dramatically changed those numbers – as well as the popularity of esthetic posterior composites. One study found a failure rate of composite fillings of only 13.7% at eight years, and another with a 40-50% failure after 10 years.

Experts admit that any practical data on composite longevity is skewed by the constant improvements and modifications of the products, which continues to be appealing for both dentists and patients.

Mercury Concerns Rising: Then and Now

The real hot spot on the amalgam versus composite battlefield lies in that one problematic ingredient found in metal fillings: mercury.

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Approximately half of dental amalgam compound is made of elemental mercury, which binds the mixture of silver, tin and copper to create a filling. Humans are actually exposed to mercury on a regular basis in our environment via air, water, and food but the negligible risks of mercury poisoning through amalgam fillings alarmed some 19th Century dentists.

The American Society of Dental Surgeons (ASDS) deemed the use of amalgam to be malpractice in 1943, forcing its members to sign a pledge they wouldn’t use it. As a result, ASDS membership declined and they disbanded in 1856. Shortly after, the American Dental Association (ADA) was founded, taking the position from the outset that amalgam was safe to use in dentistry. That stance hasn’t changed since 1859.

While the release of mercury vapor during the placement or removal of restorations is of little danger to patient or dentist, there have been cases of patients experiencing adverse symptoms over time that may be attributed to mercury exposure. Consumer advocacy groups have taken the ADA to court over such concerns, and “mercury-free” dentists have taken up the cause against amalgam.

The Food and Drug Administration (FDA) concurs that the majority of evidence shows the exposure in amalgam fillings doesn’t impact the general population. They note a small group of potentially high-risk people who should seek non-amalgam restorations instead:

  • Pregnant women and those planning to become pregnant
  • Nursing mothers and their infants
  • Children younger than six
  • Those with pre-existing neurological disease
  • People with impaired kidney function
  • People with allergies or heightened sensitivities to mercury or other amalgam components

The FDA also does not recommend the removal or replacement of existing amalgam fillings that are in good condition, unless deemed medically necessary, as it could damage the tooth structure and needlessly increase mercury exposure.

Jumping into the fray, the World Health Organization (WHO) aims for a “global phase out” of dental mercury and a general reduction of the use of mercury in all sectors, based on environmental impacts of approximately 6% in water waste and air pollution. In addition to the ADA, numerous public health agencies such as the Mayo Clinic and the U.S. Environmental Protection Agency have publicly maintained the safety and effectiveness of amalgam.

Choosing Sides

The war over the safety, efficacy, and affordability of either amalgam or composite fillings continues to this day, but so do the advancements in technology and innovation over the centuries. The ADA’s support of amalgam use hasn’t wavered, and millions of dentists address their treatment plans accordingly.

However, dentists and patients alike can appreciate the evolution of quality in composite products whether their agenda is based in health and safety, environmental concerns, or simply esthetic. Choice is always a common ground.

 


 

Susan Richards

About the Author: Susan Richards is a staff writer at DOCS Education. With over 20 years of experience in local journalism and business marketing, Susan’s career includes award-winning feature writing, as well as creating content with context for a wide variety of industries.

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