Are dental fillings safe?

Source: Best Health magazine, March/April 2014; Image: Thinkstock

Fillings are a protective measure for holes that can be created by plaque, a sticky coating of germs that forms on teeth every day. Among Canadian adults, 96 percent have at least one tooth that is either decayed or has been filled (the average is at least 10); Canada’s teens have, on average, at least two decayed or filled teeth.

Brushing your teeth 20 minutes after eating helps prevent plaque; otherwise, it begins to erode teeth’s protective enamel. (Brushing within 20 minutes of eating may actually be harmful to teeth that have just been exposed to acidic food and drink. Surprisingly, chewing gum immediately after meals is a good way to stimulate saliva flow, which neutralizes any acids in the mouth.) Cavities that are left unfilled can grow bigger and eventually affect nerves, create pain, cause teeth fracture or abscess (infection) and, finally, destroy tooth pulp, which may lead to tooth loss.

Dentists use different materials to fill cavities. But some health study headlines and Internet chatter have raised concerns over the safety of these mat­erials. And beyond the material, dentists have other considerations that determine which type they will use, including durability, installation technique, cost and aesthetics.

The most commonly used filling materials’and those that have been in the headlines’are silver amalgam and composite resin. Here’s what you need to know about their safety.

Silver amalgam

This alloy of silver, tin, copper and mercury has been used as a filling material for more than 165 years. It is commonly referred to as a silver filling.

Dentists have disagreed over its safety since the 1840s. The concern stems from the fact that the metal mixture contains elemental mercury, which studies show causes health problems at high exposures, explains Dr. Ben Balevi, a Vancouver-based dentist who has examined the evidence-based research. These problems can include kidney and brain damage.

‘Dental amalgams do release trace amounts of mercury,’ says Dr. Peter Doig, president of the Canadian Dental Association (CDA), and a dentist in Dauphin, Man. But the CDA and Health Canada agree that the amount released does not pose any health risk to the average Canadian.

Nevertheless, a community of dentists in Canada and the U.S. called the International Academy of Oral Medicine and Toxicology (IAOMT) argues against the use of silver amalgams. Says Dr. David Warwick, a dentist in Hanna, Alta., and a member of the IAOMT, ‘Studies that measure mercury in our bodies clearly show you absorb it from having even one silver amalgam.’ According to the IAOMT, this may result in an increased risk of diseases, including Alzheimer’s and multiple sclerosis. Health Canada and the CDA insist there is no credible evidence to back these claims.

Why the debate? Much of the controversy hinges on how hard it is to determine the amount of mercury in our bodies from fillings. For example, two studies that looked at the same Can­adian Health Measures Survey reached opposing conclusions on how much mercury we are exposed to via amalgams.

IAOMT points out that Norway, Denmark and Sweden have either banned or restricted the use of amalgams. However, they did so over environmental concerns (in Denmark and Sweden, health was also a concern), as use and disposal by dentists is largely unmonitored.

Composite resins

Even though silver amalgam is considered safe, and is less expensive than resins, Canadian dentists often now choose composite resins instead.

In 2012, a study in Pediatrics made headlines when it concluded that children with fillings made with bisphenol A gly­cidyl methacrylate (bis-GMA)-based composites’which are white resin fillings’had a greater likelihood of increased moodiness and aggression. (In 2008, the Canadian government banned bisphenol-A [BPA] in baby bottles over concerns for the brain, behaviour and prostate glands of infants and children.) Because composite resin fillings are fast replacing amalgams, and plastic sealants are increasingly being painted on children’s molars to prevent cavities, there has been cause for concern. Sealants are made of resin-based materials, and both resin fillings and sealants made of bis­phenol A dimethacrylate (bis-DMA) may release BPA continuously as the material degrades. Trace amounts of BPA from the manufacturing process may also be present for a short period of time immediately after placement in the teeth of bis-DMA and bis-GMA materials (fillings with bis-GMA are more commonly used in Canada), according to the American Dental Association.

So should you worry about that 2012 Pediatrics study? Balevi, Warwick and Doig all point out that it didn’t measure the actual exposure to BPA, and that the self-reported behaviour changes were rife with bias. ‘Some clinical studies have shown trace amounts of BPA in the saliva of patients immediately after they received a plastic dental filling. These were well below acceptable levels, and became undetectable a couple of hours later,’ says Balevi. ‘Furthermore, none of these studies found an association between short-term trace exposure to BPA and any deleterious health outcome.’

Interestingly, only a month after the study in Pediatrics, the same author published a study in NeuroToxicology that said there were no significant adverse effects from bis-GMA composites.

Concerned patients can ask their dentist which material will be used’bis-GMA materials are the safer option over bis-DMA, say Doig and Warwick. (There are no bis-free composite resin fillings.) Heath Canada has not placed restrictions on dental materials that may release BPA because they are within safety margins for exposure.

Bottom line

Health Canada approves silver amalgam use with one exception: the two to three percent of the population who have allergic hypersensitivity to these fillings (a condition that is hard to verify with allergy tests).

Every dentist interviewed for this article agrees there is no reason to remove silver fillings and replace them with something else unless there is a clear risk posed, such as allergic hypersensitivity. The removal process does pose an increased risk of exposure to mercury’but there is no agreement on how much danger it poses. If you are having fillings removed, ask your dentist if he or she will use a rubber dam (a barrier put over teeth to prevent particles from being swallowed). And ask if your dentist will follow IAOMT removal guidelines.

‘Maintaining healthy oral habits is key to preventing tooth decay, and avoiding the need to replace a filling. When this is needed, it’s often due not to failure of the material, but rather the continual erosion of the tooth,’ says Doig. And, he adds, while there is a hunt for the next best filling material, nothing tested in recent years has matched the efficiency of composite resin or silver amalgam.

This article originally appeared in the March/April 2014 issue of Best Health. Subscribe today to get the full Best Health experience’and never miss an issue!