Mercury test may overestimate exposure from dental amalgam fillings

A common test used to determine mercury exposure from dental amalgam fillings may significantly overestimate the amount of the toxic metal released from fillings, according to University of Michigan researchers.

Scientists agree that dental amalgam fillings slowly release mercury vapor into the mouth. But both the amount of mercury released and the question of whether this exposure presents a significant health risk remain controversial.

Public health studies often make the assumption that mercury in urine (which is composed mostly of inorganic mercury) can be used to estimate exposure to mercury vapor from amalgam fillings. These same studies often use mercury in hair (which is composed mostly of organic mercury) to estimate exposure to organic mercury from a person's diet.

But a U-M study that measured mercury isotopes in the hair and urine from 12 Michigan dentists found that their urine contained a mix of mercury from two sources: the consumption of fish containing organic mercury and inorganic mercury vapor from the dentists' own amalgam fillings.

"These results challenge the common assumption that mercury in urine is entirely derived from inhaled mercury vapor," said Laura Sherman, a postdoctoral research fellow in the Department of Earth and Environmental Sciences and lead author of a paper in the journal Environmental Science & Technology. A final version of the paper was published online March 20.

"These data suggest that in populations that eat fish but lack occupational exposure to mercury vapor, mercury concentrations in urine may overestimate exposure to mercury vapor from dental amalgams. This is an important consideration for studies seekingMeasuring mercury: Common test may overestimate exposure from dental amalgam fillings

ANN ARBOR—A common test used to determine mercury exposure from dental amalgam fillings may significantly overestimate the amount of the toxic metal released from fillings, according to University of Michigan researchers.

Scientists agree that dental amalgam fillings slowly release mercury vapor into the mouth. But both the amount of mercury released and the question of whether this exposure presents a significant health risk remain controversial.

Public health studies often make the assumption that mercury in urine (which is composed mostly of inorganic mercury) can be used to estimate exposure to mercury vapor from amalgam fillings. These same studies often use mercury in hair (which is composed mostly of organic mercury) to estimate exposure to organic mercury from a person's diet.

But a U-M study that measured mercury isotopes in the hair and urine from 12 Michigan dentists found that their urine contained a mix of mercury from two sources: the consumption of fish containing organic mercury and inorganic mercury vapor from the dentists' own amalgam fillings.

"These results challenge the common assumption that mercury in urine is entirely derived from inhaled mercury vapor," said Laura Sherman, a postdoctoral research fellow in the Department of Earth and Environmental Sciences and lead author of a paper in the journal Environmental Science & Technology. A final version of the paper was published online March 20.

"These data suggest that in populations that eat fish but lack occupational exposure to mercury vapor, mercury concentrations in urine may overestimate exposure to mercury vapor from dental amalgams. This is an important consideration for studies seeking to determine the health risks of mercury vapor inhalation from dental amalgams," said U-M biogeochemist Joel D. Blum, a co-author of the paper and a professor in the Department of Earth and Environmental Sciences.

The study by Sherman, Blum and their colleagues demonstrates that mercury isotopes can be used to more accurately assess human exposure to the metal—and the related health risks—than traditional measurements of mercury concentrations in hair and urine samples. Specifically, isotopes provide a novel chemical tracer that can be used to "fingerprint" both organic mercury from fish and inorganic mercury vapor from dental amalgams.

Mercury is a naturally occurring element, but more than 2,000 tons are emitted into the atmosphere each year from human-generated sources such as coal-fired power plants, small-scale gold-mining operations, metals and cement production, incineration and caustic soda production.

This mercury is deposited onto land and into water, where micro-organisms convert some of it to methylmercury, a highly toxic organic form that builds up in fish and the animals that eat them, including humans. Effects on humans include damage to the central nervous system, heart and immune system. The developing brains of fetuses and young children are especially vulnerable.

Inorganic mercury can also cause central nervous system and kidney damage. Exposure to inorganic mercury occurs primarily through the inhalation of elemental mercury vapor. Industrial workers and gold miners can be at risk, as well as dentists who install mercury amalgam fillings—though dentists have increasingly switched to resin-based composite fillings and restorations in recent years.

About 80 percent of inhaled mercury vapor is absorbed into the bloodstream in the lungs and transported to the kidneys, where it is excreted in urine. Because the mercury found in urine is almost entirely inorganic, total mercury concentrations in urine are commonly used as an indicator, or biomarker, for exposure to inorganic mercury from dental amalgams.

But the study by Sherman, Blum and their colleagues suggests that urine contains a mix of inorganic mercury from dental amalgams and methylmercury from fish that undergoes a type of chemical breakdown in the body called demethylation. The demethylated mercury from fish contributes significantly to the amount of inorganic mercury in the urine.

The U-M scientists relied on a natural phenomenon called isotopic fractionation to distinguish between the two types of mercury. All atoms of a particular element contain the same number of protons in their nuclei. However, a given element can have various forms, known as isotopes, each with a different number of neutrons in it nucleus.

Mercury has seven stable (nonradioactive) isotopes. During isotopic fractionation, different mercury isotopes react to form new compounds at slightly different rates. The U-M researchers relied on a type of isotopic fractionation called mass-independent fractionation to obtain the chemical fingerprints that enabled them to distinguish between exposure to methylmercury from fish and mercury vapor from dental amalgam fillings. to determine the health risks of mercury vapor inhalation from dental amalgams," said U-M biogeochemist Joel D. Blum, a co-author of the paper and a professor in the Department of Earth and Environmental Sciences.

The study by Sherman, Blum and their colleagues demonstrates that mercury isotopes can be used to more accurately assess human exposure to the metal—and the related health risks—than traditional measurements of mercury concentrations in hair and urine samples. Specifically, isotopes provide a novel chemical tracer that can be used to "fingerprint" both organic mercury from fish and inorganic mercury vapor from dental amalgams.

Mercury is a naturally occurring element, but more than 2,000 tons are emitted into the atmosphere each year from human-generated sources such as coal-fired power plants, small-scale gold-mining operations, metals and cement production, incineration and caustic soda production.

This mercury is deposited onto land and into water, where micro-organisms convert some of it to methylmercury, a highly toxic organic form that builds up in fish and the animals that eat them, including humans. Effects on humans include damage to the central nervous system, heart and immune system. The developing brains of fetuses and young children are especially vulnerable.

Inorganic mercury can also cause central nervous system and kidney damage. Exposure to inorganic mercury occurs primarily through the inhalation of elemental mercury vapor. Industrial workers and gold miners can be at risk, as well as dentists who install mercury amalgam fillings—though dentists have increasingly switched to resin-based composite fillings and restorations in recent years.

About 80 percent of inhaled mercury vapor is absorbed into the bloodstream in the lungs and transported to the kidneys, where it is excreted in urine. Because the mercury found in urine is almost entirely inorganic, total mercury concentrations in urine are commonly used as an indicator, or biomarker, for exposure to inorganic mercury from dental amalgams.

But the study by Sherman, Blum and their colleagues suggests that urine contains a mix of inorganic mercury from dental amalgams and methylmercury from fish that undergoes a type of chemical breakdown in the body called demethylation. The demethylated mercury from fish contributes significantly to the amount of inorganic mercury in the urine.

The U-M scientists relied on a natural phenomenon called isotopic fractionation to distinguish between the two types of mercury. All atoms of a particular element contain the same number of protons in their nuclei. However, a given element can have various forms, known as isotopes, each with a different number of neutrons in it nucleus.

Mercury has seven stable (nonradioactive) isotopes. During isotopic fractionation, different mercury isotopes react to form new compounds at slightly different rates. The U-M researchers relied on a type of isotopic fractionation called mass-independent fractionation to obtain the chemical fingerprints that enabled them to distinguish between exposure to methylmercury from fish and mercury vapor from dental amalgam fillings.

Fluoride in Drinking Water Cuts Tooth Decay in Adults

A new study conducted by researchers at the University of North Carolina at Chapel Hill and the University of Adelaide, Australia, has produced the strongest evidence yet that fluoride in drinking water provides dental health benefits to adults, even those who had not received fluoridated drinking water as children.

In the first population-level study of its kind, the study shows that fluoridated drinking water prevents tooth decay for all adults regardless of age, and whether or not they consumed fluoridated water during childhood.

Led by UNC School of Dentistry faculty member Gary Slade, the study adds a new dimension to evidence regarding dental health benefits of fluoridation.

"It was once thought that fluoridated drinking water only benefited children who consumed it from birth," explained Slade, who is John W. Stamm Distinguished Professor and director of the oral epidemiology Ph.D. program at UNC. "Now we show that fluoridated water reduces tooth decay in adults, even if they start drinking it after childhood. In public health terms, it means that more people benefit from water fluoridation than previously thought."

The researchers analyzed national survey data from 3,779 adults aged 15 and older selected at random from the Australian population between 2004 and 2006. Survey examiners measured levels of decay and study participants reported where they lived since 1964. The residential histories of study participants were matched to information about fluoride levels in community water supplies. The researchers then determined the percentage of each participant's lifetime in which the public water supply was fluoridated.

The results, published online in the Journal of Dental Research, show that adults who spent more than 75 percent of their lifetime living in fluoridated communities had significantly less tooth decay (up to 30 percent less) when compared to adults who had lived less that 25 percent of their lifetime in such communities.

"At this time, when several Australian cities are considering fluoridation, we should point out that the evidence is stacked in favor of long-term exposure to fluoride in drinking water," said Kaye Roberts-Thomson, a co-author of the study. "It really does have a significant dental health benefit."

Postmenopausal women who have smoked are at much higher risk of losing their teeth

Postmenopausal women who have smoked are at much higher risk of losing their teeth than women who never smoked, according to a new study published and featured on the cover of the Journal of the American Dental Association by researchers at the University at Buffalo.

The study involved 1,106 women who participated in the Buffalo OsteoPerio Study, an offshoot of the Women’s Health Initiative, (WHI), the largest clinical trial and observational study ever undertaken in the U.S., involving more than 162,000 women across the nation, including nearly 4,000 in Buffalo.

The UB study is the first to examine comprehensive smoking histories for participants that allowed the researchers to unravel some of the causes behind tooth loss in postmenopausal women who smoked.

The study, which appears in the journal’s current issue is available at http://jada.ada.org/content/144/3/252.full.

Smoking has long been associated with tooth loss, but postmenopausal women, in particular, experience more tooth loss than their male counterparts.

“Regardless of having better oral health practices, such as brushing and flossing, and visiting the dentist more frequently, postmenopausal women in general tend to experience more tooth loss than men of the same age,” says Xiaodan (pronounced Shee-ao-dan) Mai, a doctoral student in epidemiology in the UB Department of Social and Preventive Medicine in the School of Public Health and Health Professions. “We were interested in smoking as a variable that might be important.”

While fewer adults lose their teeth now than in past decades, tooth loss is associated with poor health outcomes, including stroke, cancer, rheumatoid arthritis and diabetes.

In the UB study, heavy smokers -- defined as those who had at least 26 pack-years of smoking, or the equivalent of having smoked a pack a day for 26 years -- were nearly twice as likely to report having experienced tooth loss overall and more than six times as likely to have experienced tooth loss due to periodontal disease, compared to those who never smoked.

Participants provided information to researchers using a detailed questionnaire covering smoking history. Each participant also underwent a comprehensive oral examination and reported to the dental examiners reasons for each tooth lost. In some cases, the patient’s dental records also were reviewed.

“We found that heavy smokers had significantly higher odds of experiencing tooth loss due to periodontal disease than those who never smoked,” explains Mai. “We also found that the more women smoked, the more likely they experienced tooth loss as a result of periodontal disease.”

On the other hand, they found that smoking was a less important factor in tooth loss due to caries. That’s an important distinction, says Mai.

“Periodontal disease is a chronic, inflammatory condition that may be related to the development of cancer,” she explains.

The paper notes that cigarette smoke may accelerate periodontal disease and that other studies suggest that chemicals found in smoke may favor plaque-forming bacteria that could reduce the ability of saliva to be antioxidative. Nicotine also has been shown to reduce bone density and bone mineral factors while estrogen hormones have been found to be lower among women who smoke.

Mai is now interested in pursuing research that could determine whether smokers with periodontal disease are at even greater risk for certain cancers than smokers without periodontal disease.

“Tooth loss due to periodontal disease is a prevalent condition among postmenopausal women that severely impacts their dietary intake, aesthetics, and overall quality of life,” says Mai. “Women now have yet another, very tangible reason for quitting smoking.”

- See more at: http://www.buffalo.edu/news/releases/2013/03/002.html#sthash.c2iyIrI2.dpuf