Let’s talk about silver (or amalgam) fillings. Silver or amalgam dental fillings have been used for hundreds of years due to being anti-bacterial and durable. Silver is a natural antibiotic. Amalgam fillings stand up well to the wear and tear of daily chewing, so they are a suitable choice for restoring a tooth after a cavity. Amalgam is an inexpensive option for a dental filling.
The drawbacks to using amalgam fillings are that they are not an aesthetic match to tooth color, there are health concerns with the mercury contained in the amalgam, and there are functional issues I’ll discuss at the end of this blog post.
Amalgam fillings were first used in ancient China. In modern history, amalgam fillings have been used almost 200 years. They have a long track record.
Amalgam fillings are made of 50% mercury, 30% silver, 10% tin, 5% copper, and 5% zinc. Tin, copper, and zinc prevent corrosion and limit expansion. Silver is antibacterial, preventing decay around the edges of the filling. Mercury is a wetting agent to help these metal particles slide past each other during filling placement, and mercury also helps the setting reaction produce a stronger, more durable filling. Without mercury, amalgam fillings would be brittle, and would crumble and fall out of the tooth.
Mercury is found in different forms:
- Organic methylmercury
- Inorganic mercury
- Elemental mercury
Methyl mercury is the most harmful to health, and is the form found in fish. If you are concerned about having amalgam fillings in your mouth, first consider how much fish you eat. Pregnant women and young children should be especially aware of fish intake. Consider these guidelines from the Environmental Protection Agency (EPA).
Inorganic mercury is found in industry. Health problems from inorganic mercury are unlikely because you’d have to do something unusual like eat a battery or use imported (i.e., unregulated) skin-bleaching creams.
Elemental mercury is found in dental amalgam fillings, or from a broken thermometer.
Health problems related to mercury (specifically methyl mercury) include impaired nervous system development, reproductive system impairment, kidney damage, and other problems. We are exposed to mercury by eating fish, through dental fillings, through industrial processes including burning coal, and from traces in nature.
Here is the big question: are dental amalgam fillings safe?
The answer: probably, and we don’t know for sure one way or the other.
There are so many logical leaps that have to be made to blame dental amalgam for health problems that it is unlikely that they are the source of health problems.
Consider this: researchers placed dental amalgam fillings in sheep’s teeth and tested the level of mercury in their kidney tissue several months later. The study found that mercury levels were higher in their kidneys, and kidney function decreased. That’s bad, right? Amalgam fillings are bad for people too, right?
Not so fast, my friends. The quality of a dental amalgam filling changes based on the skill of the dentist. A dental amalgam placed with high compression forces has a lot of mercury pressed out. Did the dentist smash that filling well? If not, the filling will have a higher mercury content. While the sheep study states that the sheep were under general anesthesia and the fillings were placed using “standard dental procedures,” I’d still like to know more about how well these fillings were done.
My second concern about this study is that sheep graze seven to eleven hours a day. Those dental amalgams were subject to a lot more wear and tear than a person would ever subject them to. It’s wrong to conclude that a person with amalgam fillings would have the same exposure to mercury as the sheep in the study.
Trace amounts of mercury vapor and methyl mercury (CH3Hg+) have been found in the mouth. The more amalgam fillings you have, the higher these trace amounts will be. Are these trace amounts enough to cause health problems? The only way to know your mercury levels for sure is to have your blood or urine tested for mercury levels. Acceptable levels, or levels that won’t cause health problems, are below 5 ng/ml (nanograms per millileter) or mercury in the blood, or 20 ng/ml in the urine. Even above these levels health problems may not develop.
This is from the Mayo Clinic:
“Members of the public will occasionally become concerned about exposure to mercury from dental amalgams… A small amount of mercury (2-20 mcg/day) is released from a dental amalgam when it was mechanically manipulated, such as by chewing. The habit of gum chewing can cause release of mercury from dental amalgams greatly above normal. The normal bacterial flora present in the mouth converts a fraction of this to Hg(+2) and CH(3)Hg(+), which was shown to be incorporated into body tissues. The World Health Organization safety standard for daily exposure to mercury is 45 mcg/day. Thus, if one had no other source of exposure, the amount of mercury released from dental amalgams is not significant.(1) Many foods contain mercury. For example, commercial fish considered safe for consumption contain <0.3 mcg/g of mercury, but some game fish contain >2.0 mcg/g and, if consumed on a regular basis, contribute to significant body burdens.”
This is from the EPA:
“Since the 1990s, several federal agencies have reviewed the scientific literature looking for links between dental amalgam and health problems. According to the Centers for Disease Control and Prevention (CDC), there is little scientific evidence that the health of the vast majority of people with dental amalgam is compromised, nor that removing amalgam fillings has any beneficial effect on health.
“A 2004 review of the scientific literature conducted for the U.S. Public Health Service found “insufficient evidence of a link between dental mercury and health problems, except in rare instances of allergic reaction.”
This is from the FDA:
“Dental amalgam contains elemental mercury. It releases low levels of mercury vapor that can be inhaled. High levels of mercury vapor exposure are associated with adverse effects in the brain and the kidneys.
“FDA has reviewed the best available scientific evidence to determine whether the low levels of mercury vapor associated with dental amalgam fillings are a cause for concern. Based on this evidence, FDA considers dental amalgam fillings safe for adults and children ages 6 and above. The amount of mercury measured in the bodies of people with dental amalgam fillings is well below levels associated with adverse health effects. Even in adults and children ages 6 and above who have fifteen or more amalgam surfaces, mercury exposure due to dental amalgam fillings has been found to be far below the lowest levels associated with harm. Clinical studies in adults and children ages 6 and above have also found no link between dental amalgam fillings and health problems.
“There is limited clinical information about the potential effects of dental amalgam fillings on pregnant women and their developing fetuses, and on children under the age of 6, including breastfed infants. However, the estimated amount of mercury in breast milk attributable to dental amalgam is low and falls well below general levels for oral intake that the Environmental Protection Agency (EPA) considers safe. FDA concludes that the existing data support a finding that infants are not at risk for adverse health effects from the breast milk of women exposed to mercury vapor from dental amalgam. The estimated daily dose of mercury vapor in children under age 6 with dental amalgams is also expected to be at or below levels that the EPA and the Centers for Disease Control and Prevention (CDC) consider safe. Pregnant or nursing mothers and parents with young children should talk with their dentists if they have concerns about dental amalgam.”
We know that mercury exposure at high levels is bad. This is documented in populations that rely heavily on fish in their diet, or in populations exposed to industrial spills. (See this report from the World Health Organization for more information.) We know that mercury vapor is bad because vapors are more easily absorbed into the body than mercury in liquid or solid form.
It remains unknown whether mercury at trace levels caused by dental amalgams are enough to be harmful to health or not. Making this conclusion would be similar to saying we shouldn’t take Aspirin for a headache because an Aspirin overdose will make you bleed to death. Better research is needed.
Is it possible that trace amounts of mercury can cause health problems? Yes, it is possible, but this is conjecture. If I have a patient asking to have their amalgam fillings removed for health reasons, I will remove their fillings, because it is unknown.
It may sound like I’m pro-amalgam. Let’s just say I’m not anti-amalgam.
Do I recommend replacing amalgam fillings? Yes, I do. I recommend replacing most amalgams for functional reasons, and secondarily for health concerns.
Consider this: once an amalgam filling is removed it is treated as hazardous waste. Dentists take precautions to prevent that amalgam (specifically the mercury) from making its way into the waste water system (and eventually into fish) or into landfills. The suction line on dental chairs has an amalgam separator. Crumbs of amalgam filling are disposed of by a hazardous waste company rather than being thrown out in the regular trash. An amalgam filling is more hazardous out of your mouth than in it.
Look at these two photos:
This amalgam filling looks pretty darn good. It is intact and free of cracks. The margin where the filling and the tooth meet are largely intact with minimal staining but no decay.
Once the amalgam filling is removed, it doesn’t look so good. We see cracks in the tooth and a lot of stain. The stain could be tertiary dentin, or decay. Dark black decay is very slowly progressing decay (when contrasted with a light brown or yellowish cavity that is very fast progressing). If a silver filling gets a cavity underneath, the antibacterial silver will slow down its progress. Decay may be present for a long time before causing noticeable problems. This is a concern, as it may not cause symptoms until the tooth needs a root canal, a crown, or even extraction.
Why are there cracks in the tooth under this amalgam filling? First, amalgam expands and contracts with temperature changes caused by hot food vs. a cold drink. The expansion and contraction of amalgam happens at a different rate than the natural dentin and enamel in the tooth. The strain of the expanded filling may cause the tooth to crack. (Based on the location of the cracks in the photo, this is the most likely cause.)
Second, cracks can be caused by the shape of the filling, or the way it fits into the tooth. Amalgam doesn’t bond to the tooth. It is held in place mechanically, that is, the shape of the filling in the tooth is locked into place to prevent it from falling out. (Contrast this with composite fillings that are bonded to the tooth; the shape of the tooth doesn’t need undercuts like it does for an amalgam filling.) The shape of an amalgam filling may act as a wedge, subtly splitting or cracking the tooth over years of use.
We have better filling materials today. Composite resin fillings, or bonded fillings, are a better option. They match the color of the tooth, so they look better. Composite fillings bond to the tooth, providing better support to the tooth than amalgam. The longevity of composite compares well to amalgam unless you have a high decay risk. Composite fillings are my first choice. I only place two or three amalgam fillings per year – for gold crown repair or when it is not possible to keep a tooth dry long enough to finish a composite filling.
There are rational precautions that should be taken when removing an amalgam filling. Use of a rubber dam will prevent swallowing an amalgam debris. Water spray and suction are also used to keep the tooth clean as the amalgam is removed.
When I remove an amalgam, I can tell how well it was placed. When the drill cleans out the old filling, it may turn to mushy powder. This is a sign that it was not condensed well and has a high mercury content. If filling comes out in small chunks of silver metal, then it was condensed well and has a lower mercury content.
Don’t go to the extreme of having mercury blood levels checked. If you’re considering having silver fillings replaced, do it because there are better filling options for your tooth. The unknown health concerns then become irrelevant.
Small, clean amalgam fillings don’t need to be replaced. Consider replacing medium or large amalgam fillings.