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This research, which analyzed data from nearly 15,000 individuals, is the first to demonstrate a relationship between dental fillings and mercury exposure in a nationally representative population. The results were published online last week and will be available in the print edition of the journalEcotoxicology and Environmental Safety in December.

«Tooth decay is one of the most prevalent chronic diseases,» said Lei Yin, a scientist in the department of environmental health science and the study’s lead author. «I think a majority of people have experienced dental fillings, but the kind of materials the dentist uses isn’t something that’s really discussed.»

Mercury exposure from dental fillings is not a new concern, but previous studies were inconsistent and limited, according to Xiaozhong «John» Yu, assistant professor of environmental health science and co-author of the study.

«This study is trying to provide the most accurate levels of exposure, which will form the scientific basis to make future risk assessment,» Yu said, adding that the study was the first to also control for age, education, ethnicity, race, gender, smoking and seafood consumption, which is a known contributor to mercury levels in the body.

The researchers further analyzed exposure by specific types of mercury and found a significant increase in methyl mercury, the most toxic form of mercury, related to dental fillings. Yu said this result suggests the human gut microbiota, a collection of microorganisms living in the intestines, may transform different types of mercury.

Dental amalgam has been the go-to dental filling material for more than 150 years, because it’s affordable and durable. However, about half of the compound contains mercury, a heavy metal known to be toxic at high levels, causing brain, heart, kidney, lung and immune system damage. New research suggests that methyl mercury may cause damage even at low levels.

«As toxicologists, we know that mercury is poison, but it all depends on the dose. So, if you have one dental filling, maybe it’s OK. But if you have more than eight dental filings, the potential risk for adverse effect is higher,» Yu said. People with numerous dental fillings who are also exposed to mercury from other sources, such as seafood or work environments, are most at risk.

The results show that individuals with more than eight fillings had about 150 percent more mercury in their blood than those with none. The average American has three dental fillings, while 25 percent of the population has 11 or more fillings.

According to its website, the U.S. Food and Drug Administration considers dental amalgam fillings safe for adults, but says, «pregnant women and parents with children under six who are concerned about the absence of clinical data as to long-term health outcomes should talk to their dentist.»

The study also looked at dental composite resins, a mercury-free alternative for dental fillings that can release small amounts of bisphenol A, or BPA, which may cause developmental or reproductive damage. The results found no association between dental fillings and urinary BPA, but further research is needed to understand BPA exposure from resin-based materials.

«It’s important for doctors and patients to be informed in their selections,» Yin said. «We now have an excellent starting point to evaluate the potential risk of dental material on human health.»

Although it is a technical term, ‘dental occlusion’ is increasingly on the minds of many patients following a routine visit to the dentist. Doctor’s offices diagnose problems related to a bad bite such as a shifted midline, gaps between teeth, crowding, crossbites and missing teeth.

Dental occlusion is simply the contact made between the top and bottom teeth when closing the mouth. Teeth may be perfectly aligned or they may present alterations with varying levels of severity.

Two new studies, carried out in collaboration between the Department of Physiology at the University of Barcelona (Spain) and the University of Innsbruck (Austria), have confirmed a less obvious relationship between an imperfect bite and postural control.

Another aspect to be highlighted is that although this relationship may seem statistically weak, it grows stronger when a person experiences fatigue or when instability is a factor.

«When there is a malocclusion, it is classified according to scientifically established criteria. What is relevant in the study is that malocclusions have also been associated with different motor and physiological alterations,» explains Sonia Julià-Sánchez to Sinc, the main author of the studies and a researcher at the Catalan university.

Both studies, whose results have been published in Motor Control and Neuroscience Letters, provide conclusive data which show that postural control is improved -both in static and dynamic equilibrium- when different malocclusions are corrected by positioning the jaw in a neutral position.

This relationship is not as obvious in everyday static conditions, although there may be conditions associated with pathologies, such as obesity, that worsen the body’s instability, thus decreasing postural control and increasing the risk of falls.

This relationship in athletes can play a crucial role in how well they ultimately perform as well as in the prevention of injuries such as sprains, strains and fractures caused by unexpected instability as fatigue increases and motor control capacity decreases.

«Therefore, it would be helpful for both the general population and athletes to consider correcting dental occlusions to improve postural control and thus prevent possible falls and instability due to a lack of motor system response,» adds Julià-Sánchez.

A reciprocal influence

«Postural control is the result of a complex system that includes different sensory and motor elements arising from visual, somatosensory and vestibular information,» explains the expert.

In recent years there has been increasing scientific interest in the relationship between the stomatognathic system (the set of organs and tissues that allow us to eat, talk, chew, swallow and smile) and postural control.

The link may have a neurophysiological explanation. There is a reciprocal influence between the trigeminal nerve and the vestibular nucleus ‑which are responsible for the masticatory function and balance control, respectively‑ as well as between the muscles of mastication and of the neck.

This influence would explain why dental malocclusions negatively affect postural control. Up until now, however, there was no conclusive research.

«The main problem stems from the fact that the majority of these studies had statically assessed balance under conditions of total stability, which in practice has little actual application in the control of posture while in action,» points out Julià-Sánchez.

The first study took into account the type of dental occlusion as well as whether there had been previous orthodontic treatment. The results showed that alterations in alignment of the teeth were related to poorer control of static balance.

The second study assessed the type of dental occlusion, control of posture and physical fatigue in order to analyze a possible relationship among these factors. The analysis demonstrated that balance improved when malocclusions were corrected, and that the latter had a greater impact on postural control when subjects were fatigued than when they were rested.

«When the subjects were tired their balance was worse under both stable and unstable conditions. Under static conditions, the factor that had the greatest impact on imbalance was fatigue. In contrast, a significant relationship between exhaustion and dental occlusion was observed under conditions of maximum instability,» concluded Julià-Sánchez