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Dental Materials Restorative Dentistry

How safe, clinically effective, and cost-effective are composite resin and amalgam dental filling materials?

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We are very pleased to present the first Canadian Armed Forces Dental Corps’ post, by Lieutenant-Colonel Dr. Dwayne Lemon, Senior Clinical Practice Leader 

Amalgam fillingLast year, as part of its continuous quality improvement program, the Canadian Armed Forces Dental Corps initiated an evaluation of its restorative practice, particularly its choice of direct restorative materials for treating caries.

The Dental Corps asked the Canadian Agency for Drugs and Technologies in Health (CADTH) to critically appraise the existing literature on the suitability of amalgam- and resin-based composite as restorative materials. The resulting report Composite Resin and Amalgam Dental Filling Materials: A Review of Safety, Clinical Effectiveness and Cost-effectiveness was published in June 2012.

Three research questions were asked:

  1. What is the evidence for the safety of dental amalgams compared to resin composites when used as filling material on permanent teeth?
  2. What is the evidence regarding the clinical effectiveness of dental amalgams compared to resin composites when used as filling material on permanent teeth?
  3. What is the cost-effectiveness of dental amalgams compared to resin composites when used as filling materials on permanent teeth? 

An initial literature search found 386 citations which, when exposed to their inclusion criteria, was reduced to 20 articles based on 6 unique trials; two Randomised Controlled Trials (RCTs) evaluating safety of amalgam, two RCTs comparing the efficacy of amalgam and composite, and two economic studies evaluating and comparing the costs associated with the use of both filling materials.

The report’s conclusions to the above questions were:

  1. The use of amalgam dental fillings in children did not result in different neurobehavioral, renal, or immunological outcomes compared to the use of composite. Moreover, the current review revealed that further clinical research is needed to answer questions about the potential harms caused by the exposure to bisphenol A from composite materials,
  2. The comparative efficacy evaluation suggested that amalgam fillings have a greater longevity than composite materials and less demand for repair, and
  3. The initial cost for placing dental amalgam is slightly cheaper than the cost for composite fillings; however, the cost difference tends to increase when taking into considerations the longevity differences of the two materials.

Recently, results from another study1 published by researchers at the University of Michigan questioned the historical means of measuring mercury exposure attributed to dental amalgam fillings. The study found that mercury from fish consumption could account for as much as 70% of that measured in the urine of those who consume fish in their diet. In other words, mercury exposure due to amalgam—as measured in urine mercury output—could be significantly overestimated.

In light of the present dental literature evidence, including CADTH’s systematic review, the Canadian Armed Forces Dental Corps is confident in the safety of amalgam (environmental and patient) and shall be interested to review future research on composite safety. Comparing the efficacy, longevity, and cost, amalgam appears to be the better of the two products.

1. Sherman LS, et al. New Insight into Biomarkers of Human Mercury Exposure Using Naturally Occurring Mercury Stable Isotopes, Environ Sci Technol, 2013, 47 (7), pp 3403–3409 

Any opinion expressed in this article is the opinion of the author and does not constitute the official opinion or policy of the Department of National Defence or the Canadian Armed Forces.

3 Comments

  1. Ajit Auluck August 6, 2013

    Very interesting study. I am concerned about the mercury vapours generated using its use, perhaps this is more while we are removing old restorations. How safe is this practice? Perahps one of the reaons for me to use composite over amalgam is its direct bonding, less time consumption and disposal of amalgam waste. Does calculation of cost effectiveness include some of these parameters? Thanks again for this intersting literature review and brining this topic up for discussion.

    Reply
  2. Don Noble August 8, 2013

    Thank-you for publishing this study. It would seem to confirm what the profession has been saying for years, about the improved longevity and reduced cost of amalgam. It also raises the question of bisphenol A in composites, something which the “anti-amalgamists” seem to ignore.

    Certainly, as indicated in the previous comment, direct bonding does offer some advantages over amalgam, which can lead to improved retention of composites, and more conservative preparations in certain clinical situations.

    As an aside, I find that, when I discuss material choice with my patients, most are not concerned about potential risks of the materials. Their usual reason for selecting composites is based on aesthetics, their reasons for selecting amalgam are cost and longevity. Often, they simply say to me “just use whatever you think is best”.

    Again, thank-you for re-visiting this issue.

    Reply
  3. Vipul G Shukla August 11, 2013

    Interesting choice of parameters for this study, and hence the interesting conclusions drawn from it. Are longevity and cost effectiveness more important parameters than cellular toxicity and other metallo-physical characteristics? After all, a direct restoration’s primary purpose is to restore the damaged tooth back to it’s original shape, form & function. Does this mean it can be done using any material that lasts?
    What about biocompatibility?
    As a practising dentist, I conscientiously and deliberately backed off from direct amalgam restorations about 6 years ago, as I realized the silent damage that was being done by these metallic fillings. Not only is the co-efficient of set amalgam way different from enamel or dentin, the immediate toxicity from the mercury (50% of the set mass) causes the living dentin to form sclerotic dentin to protect the nerve. (If you have ever removed an old amalgam from a permanent tooth, you know the sight).
    The filling is microscopically expanding and contracting every time you have hot coffee or ice cream. The tooth cannot accommodate this behavior. Result: Microscopic cracks under cusps, and finally a cusp shear fracture or Cracked Tooth Syndrome. Au contraire, a direct resin holds the walls of the prep together.
    Lastly, Creep & Flow. No, not a new R&B band. The property of metals to expand on repetitive stress like the opposing cusps grinding into an occlusal amalgam. Again, slow expansion of the filling, tooth cannot expand, CTS or cusp shear fracture.
    Lastly, if silver mercury restorations are so safe for the body and the environment, then why are they banned in many countries in Europe already and a further debate going on in other countries?
    Which country on this planet has banned composite resin fillings? None.
    Lastly, if you want neutral, unbiased evidence about the levels of mercury vapor released during an average 24-hour cycle in an adult with say, nine amalgam fillings, read the 2003 report by the WHO released to the public, and available on the internet.
    Lastly, the mercury pollution to our lakes and rivers from dental offices is a whopping 53% or more. This mercury waste is eaten by tiny crustaceans and microbes, who get eaten by small shrimp, who are then eaten by larger fish, and the mercury keeps getting up the marine food chain, finally reaching alarming levels in the large predators like shark and tuna. And you wonder where the mercury came from in the first place?
    Then, Health Canada puts out warnings to pregnant women about how much tuna they can have during a month while pregnant. They are aware that mercury crosses the placental barrier. Agreed that this is methyl mercury, but how did it get there in the first place?
    No creature can process mercury. No lung, gill, kidney or liver can process it. It simply accumulates in body tissue.
    There was a time for amalgam fillings, there was a time for ether & even chloroform as an anesthetic, Thalidomide was also a useful sedative/anti-nausea drug once upon a time. Till we found something better. The time has passed. We must move on to better materials and techniques.
    A tough learning curve for many, who find comfort in silver amalgams, especially building tight contacts in Class IIs, but we must do better especially if we must follow the first commandment in medicine; ‘Above all, do no harm’.

    Reply

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