Dental Toxicity

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Dental Metals and Their Relationship to Neurodegenerative Diseases

Do you know someone with a neurodegenerative disease? Most people do, or you may have one yourself. A neurodegenerative disease is a “nerve-degenerating” condition—a disease where the nerves are damaged or die. Unfortunately, neurodegenerative con­ditions such as Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS) and Parkinson’s disease (PD) are becoming more common, now affecting over fifty million people worldwide.¹

Despite promising research and some helpful treatments, much about these diseases is still unknown. Science has not agreed upon a definitive cause for many of these conditions, and some would say that they “remain a mystery.” But there is a plausible cause for neurodegenerative condi­tions, though not commonly spoken about: heavy metal toxicity.²

In our everyday life, there are many sources of exposure to heavy metals, whether natural or man-made. These can include industrial waste, tailings, mining, paints, pollution, treated tim­ber, agricultural runoff and fertilizers, lead-acid batteries, some thermometers, fluorescent light bulbs, volcanic eruptions, emissions from coal-burning power stations, contaminated seafood, some medications, the water supply and even micro-plastics.^3-5 However, a commonly over­looked source of heavy metals can be found within your own body, and more specifically in your mouth! In this article, I discuss the links between heavy metals, dental metals and three common neurodegenerative diseases.⁶

DENTAL METALS

The most well-known metal found in the mouth is mercury from dental amalgam (silver/ black) fillings. Dental amalgam fillings contain about 50 percent elemental mercury,⁷ a known neurotoxin. While the exact composition may vary between brands, the elemental mercury is usually mixed in an alloy with copper, silver and tin.⁶ Amalgam fillings also may contain smaller amounts of nickel, palladium and indium, and possibly zinc, lead and cadmium.⁶ Dental amal­gams are the largest source of mercury exposure in industrialized countries, with autopsy studies showing that 60 to 95 percent of mercury depos­its in human tissues are from dental amalgams.⁸

Mercury is notorious as one of the most toxic elements on the planet.^7,9 It can target many different mechanisms and parts of the body, but it is most well-known as being toxic to the nerve cells (neurons). Mercury neurotoxicity can dis­rupt structures in cells such as the cytoskeleton and mitochondria, as well as generate harmful reactive oxygen species (ROS) and much more.10 Mercury is ten times more toxic to neurons than lead and is associated with many medical problems, including neurological disorders.^9,10 When it comes to the development of mercury-related diseases, the mercury exposures may be either sudden or chronic. Researchers have posited that mercury accumulation in the brain may be a cause of Alzheimer’s, ALS and Par­kinson’s.^4,7,10,11

Mercury can be found in the mouth in several places, including in amalgam fillings, amalgam tattoos or even in the root of the tooth if it has had a root canal procedure called an api­coectomy. In the mouth, amalgam fillings have the ability to emit mercury vapor in the form of elemental mercury, which can travel throughout the body and pose significant health threats. The vapor can travel to the lungs, teeth, gums and brain, where it can then enter the neurons and, crucially, the mitochondria.^7,8 Even the Food and Drug Administration (FDA) now acknowledges that mercury fillings release mercury vapor that can pose dangers to certain “high-risk” groups.¹²

Studies suggest that the largest exogenous source of brain mercury comes from dental mer­cury fillings.^5,9 Mercury in the brain increases in proportion to the number or surface area of amalgam fillings that a person has.⁵ Several studies have shown that individuals with amal­gam fillings can have two- to tenfold higher amounts of mercury in their brains compared to persons with no amalgam fillings.¹⁰

Have you ever left a metal object in the rain or outside? Over time, it starts to rust, wear away, chip or corrode. This same concept applies to dental metals in the mouth. Mercury fillings may be worn down from normal wear and tear or via corrosion. As they chip, are worn down and abrade, pieces can be swallowed and enter the digestive system and be reabsorbed.⁵ However, many factors influence how much cor­rosion occurs, including mouth acidity levels, certain bacteria and other factors.^13,14

Other dental materials contain metals as well, including some crowns, bridges, implants, posts, pins, wires, clasps, brackets, parts of dentures and some orthodontic or oral position­ing devices. Some have been found to contain metals such as aluminum, beryllium, chromium, cobalt, copper, gallium, gold, indium, iridium, iron, manganese, nickel, palladium, platinum, silver, tin, titanium, vanadium, zinc and others.⁶ The specific composition usually depends on the brand and type of device.

As already suggested, dental metals have the potential to do a lot of harm to nerves. Long-term exposure to heavy metals is associ­ated with nerve inflammation, damage and, in some situations, nerve death.3 Some of the effects^3,4,15 include:

• Placing stress on cell structures such as the mitochondria
• Causing misfolding of important proteins essential to health
• Breaking apart and damaging DNA
• Causing oxidative stress, characterized by “an imbalance between production and accumulation. . . in cells and tissues”¹⁶ of reactive oxygen species (ROS)—a type of free radical—and an inability to detoxify them¹⁷
• Triggering cells to die (apoptosis)

Some metals work together to damage nerves, producing synergistic effects. A little-known fact is that mercury may have exacer­bated effects when combined with other metals such as aluminum, lead, cadmium, zinc or manganese, even at levels that are considered to be “low” or “nontoxic.” Therefore, having multiple metals in your body or a combination of abnormal levels of certain metals may be a unique risk factor for worsening health.⁵

METALS AND PARKINSON’S DISEASE

Parkinson’s disease (PD) is the second most common neurodegenerative disorder (behind Alzheimer’s) and is the most common muscular function disorder. PD is known for the degenera­tion of nerve cells in the area of the brain called the substantia nigra.³ The specific nerve cells that are lost are called dopaminergic neurons. This leads to a deficiency of dopamine (a mes­senger for nerve cells), which can present as the typical motor issues seen in PD such as tremors, rigidity and bradykinesia (slowness).^3,5

Parkinson’s usually progresses slowly and presents not only as motor impairment but also in the form of psychological, cognitive and au­tonomic nervous system changes and dysfunc­tion.^3,15 PD can be difficult to study because of the slow progression and because exposures can happen years or even decades before Parkinson’s is diagnosed.

Although modern medicine considers most cases of PD to have “idiopathic” (unknown) causes,^5,15 historically, an association between environmental exposure to metals and PD was noted. In 1817, James Parkinson discovered a connection between the Industrial Revolution in England and PD. Back then, with little knowl­edge about pollution emission technologies, the release of environmental toxins such as mer­cury, arsenic and lead from coal burning was high.¹⁸ In addition, mercury was commonly used in teething powders and for treating syphilis, corresponding with a higher incidence of PD.5 In Canada, research has linked higher ambient levels of manganese metals to an increased risk of PD and a lower age at PD diagnosis.⁵

In fact, despite the claim of “idiopathic” causes, numerous studies show a strong relation­ship between PD and metals, including copper, manganese, lead, mercury, iron, bismuth, zinc, aluminum and titanium,^3,5 some of which are commonly used in dentistry. Epidemiological studies have found that the risk of PD increases with exposure to pesticides, solvents and met­als.¹⁵

Is there a connection between genetics and PD? Interestingly enough, even though fifteen genes and loci have been associated with PD, researchers believe that genetic causes can ac­count for at most 5 to 10 percent of cases. A large epidemiological study of twenty thousand pairs of twins found no definite genetic cause explain­ing the occurrence of PD, nor could any role of genetics be ascertained in the Italian community of Valcamonica, where researchers observed a high prevalence of PD in conjunction with environmental exposure to metals.⁵ With that said, there is evidence that the APOEe4 allele (a form of a gene) is associated with increased PD risk; APOEe4 increases susceptibility to nerve damage from metals such as mercury and lead.⁵

Several proteins are important when dis­cussing PD and other neurodegenerative diseas­es. These include Lewy bodies (bundles of pro­teins that form in the nerves), alpha-synuclein (a protein found within Lewy bodies thought to be a potential cause of PD), phosphorylated tau proteins (also found in Lewy bodies and affected in PD and other neurodegenerative diseases) and amyloid-beta (a protein that can form amyloid plaques, or clumps on the neurons).⁵ Metals can interfere with these proteins and can damage the mitochondria of cells.^3,15 Metals are commonly known to form free radicals, disrupting the antioxidant/free radical balance; as mentioned earlier, this can lead to nerve damage.^,3 People with PD have high production of ROS and tend to have high levels of oxidative stress,⁵ which can lead to an abnormal aggregation of proteins as well as cell death.³ Increased numbers of proteins affected by this oxidative process are found in the substantia nigra part of the brain in PD patients, where impaired mitochondrial function is also seen.⁵

Thus, environmental toxins can account for the dopaminergic nerve cell death seen in Parkinson’s, which can lead to misfolding and buildup of the alpha-synuclein proteins men­tioned earlier. Pesticides and metals such as alu­minum, cadmium, copper, iron, lead, mercury, manganese and zinc promote the aggregation of alpha-synuclein, with negative effects on PD.^5,15 In fact, as with the synergy between different metals, pesticides and metals also can work to­gether and have synergistic effects that make the situation worse.⁵ In addition, there is evidence that a-synuclein can be increased and have more toxicity due to the amyloid-beta proteins that play a role in both Parkinson’s and Alzheimer’s; mercury increases the production of amyloid-beta proteins.⁵ It is also interesting to note that mercury promotes the hyper-phosphorylation of the tau proteins, even at low doses.

As already outlined, there are multiple mechanisms whereby mercury (and other metals) can cause nerve degeneration and Parkinson’s-like symptoms. These include via damage to the mitochondria, oxidative stress, DNA alteration and protein misfolding, as well as altered copper-zinc metabolism.^3,5 Studies have found that blood mercury levels are substantially higher in Parkinson’s patients compared to non-PD patients, and people exposed to dental amalgam fillings have a sixfold higher incidence of PD compared to those without amalgam fillings.^3,5 One study showed that PD patients had significantly more mercury fillings before their Parkinson’s symptoms developed than non-PD patients.⁵ Men are twice as likely to develop PD as women, and research suggests that this could be due to hormone lev­els. Estrogen protects against mercury, while testosterone can enhance mercury toxicity.⁵ Of note, dentists are disproportionately likely as an occupation to develop PD¹⁹; researchers have found that dental profes­sionals exposed to mercury from dental amalgam fillings at work have elevated PD-related dementia and mortality.⁵

In their 2018 study titled “Metals and Parkinson’s Disease: Mecha­nisms and Biochemical Processes,” a group of international researchers provides an informative chart showing the many similarities between mercury’s effects and Parkinson’s disease pathology (reproduced in Table 1).⁵ It shows what goes on in the body as a result of mercury exposure and how those same things are also happening in PD. This does not necessar­ily mean that there is a cause-and-effect relationship between mercury and Parkinson’s, but it is shocking to see that the two sets of symptoms are almost identical.

Research also connects metals other than mercury to Parkinson-like symptoms, including cadmium—one of the most toxic metals, found in some amalgam fillings6—and copper, found in some dental materials, including crowns. Producing oxidative stress, cadmium damages or trig­gers the death of the dopaminergic neurons and can produce symptoms such as neurological disturbances, peripheral neuropathy and motor impairment.³ As for copper, although it is an essential nutrient that our bodies use for important functions, when present in excess it can cause Parkinsonian movement symptoms, degeneration of nerves and even psychiatric disturbances.^3,20

When the blood transports metals such as mercury and copper from dental restorations and implants through the body and deposits them in the brain,5 there are cells that can “eat them up” and engulf the toxic metals. One of these cell types, located in the substantia nigra, is called a neuro-melanocyte. Ordinarily, the neuro-melanocytes are involved with making dopamine, but the ingested metals can impair their ability to make it.⁵

METALS AND ALZHEIMER’S DISEASE

Alzheimer’s disease, the most common type of dementia, is a progres­sive brain disease that, like PD, involves inflammation of and damage to nerve cells.²¹ Symptoms can include memory loss, language problems and cognitive dysfunction, and may progress to disorientation and impaired communication where it is difficult to speak or even swallow.^20,22

Research not only implicates mercury in AD but has even strongly put forth mercury as a cause.^9,20 Studies show that people with AD can have two- to tenfold higher amounts of mercury in their brains compared to those without AD.^10,20 In some studies, patients with AD have had higher levels of mercury in other body tissues as well as in the blood.^9,23,24 Another study showed both mercury and manganese in the plasma to be significantly higher in people with AD compared to people without AD.²⁵ Studying exposure to dental amalgam fillings, researchers found that women who were exposed were 1.13 times more likely to have AD compared to women who were not exposed to amalgam fillings.²⁶ While this may seem like a borderline significant result, the authors of the article clearly considered amalgam a risk factor for AD.

As with PD, an interesting review article that compares seventy factors associated with AD and the effects of mercury shows extensive overlap.⁹ For example, mercury causes the production of amyloid-beta proteins, which make the amyloid plaques infamously associated with AD.^4,9 In fact, we know that mercury can cause many of the hallmarks of AD. For example:

• Mercury is associated with the genetic mutations presenilin-1 and presenilin-2 in AD through its ability to stop production of DNA in the brain. AD also has mutations in apolipoprotein E 4, which increases mercury’s toxicity. Mutations that make people more sensi­tive to metals could be related to the metabolism of metals in AD.⁹
• AD and mercury toxicity share the same abnormalities of aluminum, calcium, copper, iron, magnesium, selenium, zinc and vitamins C, E, B1 and B12.
• AD and mercury toxicity both cause inhibition of the neurotransmit­ters serotonin, dopamine, acetylcholine, glutamate and norepineph­rine.
• Both mercury toxicity and AD disrupt the same enzyme functions, including those of nitric oxide synthetase, choline acetyltransferase and cytochrome-c-oxidase.

Despite the abundant evidence that mercury and certain other metals can be neurotoxic, mainstream sources such as the Alzheimer’s Association in the U.S. persist in claiming that there is no association between AD and dental amalgam fillings.²⁷ To support their claim, the Association cites a twenty-five year-old study from 1999 funded by the National Institutes of Health (NIH), which concluded, “Hg [mercury] in dental amalgam restorations does not appear to be a neurotoxic factor in the pathogenesis of AD. The authors found that brain Hg levels are not associated with dental amalgam, either from existing amalgam restora­tions or according to subjects’ dental amalgam restoration history.”²⁸

It is important to point out the flaws in the study27 upon which the Alzheimer’s Association stakes its bold claim that mercury doesn’t seem to be a factor in AD. First, the study’s sample size was very small, which can impact the results. Thus, although the study did not find a statistically significant difference in the amount of mercury in the brains of individuals with and without AD (meaning that the numbers weren’t strong enough to show a connection), that does not mean that there wasn’t any mercury in the brain. Moreover, low amounts of mercury do not necessarily equal safety, for even low amounts have been shown to be connected to neuronal damage in AD and in general. The phosphory­lated tau in Lewy bodies found in AD furnishes one example; even at low doses, mercury pro­motes tau protein hyperphosphorylation, which can lead to nerve cell death and even demen­tia.^5,10,25,29 The World Health Organization and other UN agencies agree that there is no safe exposure threshold for mercury toxicity.³⁰

Another flaw in the 1999 study cited by the Alzheimer’s Association was its failure to consider the fact that mercury can accumulate in and affect organs all over the body, not just the brain. Looking only at the brain excludes other potentially important considerations such as gut health, which can impact AD. A third limita­tion pertains to contradictory statements in the study’s Results and Methods sections; although the researchers asserted in their Results that they had accounted for dental amalgam restoration history, in the Methods section, they disclosed that for some subjects, they only were able to get their dental history at the time of autopsy. This could have led them to underestimate the amount of mercury fillings subjects had in their lifetime, which could significantly alter the findings.

The Alzheimer’s Association also bases its claim of no association between Alzheimer’s and amalgam fillings on a March 1991 finding of the FDA’s Dental Devices Panel, which stated, at the time, that “there was no current evidence that amalgam poses any danger.” Given addi­tional research findings over the past thirty-plus years, an update to the Association’s website seems warranted, not least because of the FDA’s current recommendation that “high-risk popula­tions. . . avoid dental amalgam, if possible and appropriate.”¹² The FDA’s list of those at high risk includes “People with neurological impair­ment or kidney dysfunction” and “People who are sensitive to mercury, silver, copper, tin, or zinc” as well as young children, pregnant and nursing mothers and women planning to become pregnant.¹²

METALS AND AMYOTROPHIC LATERAL SCLEROSIS

ALS (also known as Lou Gehrig’s disease) is another common neurodegenerative disease, affecting the motor neurons of the brainstem, spinal cord and cerebral cortex.² In the general population, there are about one and a half new cases of ALS per year per hundred thousand inhabitants. Although medical science asserts that the causes are unknown, exposure to metals should be considered a possible culprit.

As with Parkinson’s and Alzheimer’s, re­search has linked ALS to heavy metal toxicity, and specifically to mercury.² Mercury toxicity typically presents as tremor, peripheral neu­ropathy (weakness, numbness and/or pain) and cortical blindness, all of which are also symp­toms of ALS. There have been several reported cases of ALS related to mercury intoxication.¹¹ In a case study of a woman with ALS, the re­searchers observed an increase in mercury and the mercury/selenium molar ratio in the blood and the motor region of the brain.¹¹ In another case where a woman exhibited neuromuscular abnormalities consistent with ALS, she had very high levels of urinary excretion of and an increased blood level of mercury, indicating mercury intoxication.²

Once again, damaged proteins play an important role in ALS. Oxidative stress can alter a protein called TDP-43, and mutations in that protein are thought to be a major cause of ALS.³¹ Interestingly, Lewy bodies play an important role not just for PD and AD, but also in ALS,³⁰ and as we have learned, metals can trigger both oxidative stress and the formation of Lewy bodies.

IT’S INDIVIDUAL

I often get asked, “Why doesn’t everyone with metals in their mouth have a neurological disease?” The way I like to explain it is, “Why doesn’t everyone who smokes cigarettes get lung cancer?”

Many possible variables can come into play to affect neurological health—not just metals. Everyone has a unique medical history and dif­ferent levels of toxic exposures. Some people may have a heightened sensitivity or allergy to metals.³² Other variables that may contribute to poor health include diet, lifestyle, toxic load and genetics.

The concept of epigenetics refers to the no­tion that the environment can turn “bad” genes on and off. It is important to understand epi­genetics because medicine will often “blame” diseases on genetics, when in fact, you can manage the condition by improving your envi­ronment. Research shows that maintaining brain and nerve health relies heavily on epigenetics and that ALS, Parkinson’s and Alzheimer’s all have epigenetic implications.^33,34 There are ac­tions that you can take to try to help the good genes to “stay on.” Science is exploring targeted approaches to address epigenetics in neurode­generative diseases.^33,34

I HAVE DENTAL METALS IN MY MOUTH—NOW WHAT?

I am also often asked, “Should I get all of the metal out of my mouth?” People ask, “If I get all of the metals out of my mouth, will this disease go away?” Unfortunately, there are no black-and-white answers to these questions.

On the one hand, there are encouraging cases in the medical and dental literature where removal of dental metals has helped to improve certain medical conditions.³⁵ For example, re­moving amalgam fillings in mercury-sensitized patients has improved the general health of patients suffering from diseases such as fibro­myalgia, chronic fatigue syndrome and other au­toimmune diseases.⁵ I have witnessed symptoms associated with heavy metal poisoning “disap­pear” or “significantly improve” after removing dental metals. However, there is no guarantee that this will be the case for everyone. Every body is different, and many other variables can affect improvement or non-improvement of a medical condition. In addition, sometimes it can be risky to remove a metal for medical reasons or due to the risk of potentially losing a tooth. It is important to consult with your dentist about your specific situation to see what may be best for you.

To address the health variables that can im­pact neurological health, I usually recommend that patients work with a health practitioner who emphasizes approaches for improving overall health. I have seen naturopathic and functional medicine doctors make a huge difference for patients with chronic diseases, even when they were told that there was not much that could be done to help them. I believe it is important to consider metals as a factor when approaching neurological diseases. I hope that more dental and medical professionals will become aware of the potential harm that metals can cause and will opt for non-metal options whenever possible.

Not all dentists have much understanding about the risks of dental metals; biological and holistic dentists are more likely to have that knowledge. These types of dentists usually have certifications and training on how to work with dental metals safely. For example, they may know extra precautions to lower the risk of mercury exposure when removing a mercury filling. They also may have more knowledge about detoxing from metal exposure and the best non-metal replacement options, if necessary. Many of these dentists can also evaluate you or refer you for testing to assess the possibility that dental metals are affecting your health. Orga­nizations such as the International Academy of Oral Medicine and Toxicology (IAOMT) are a resource to find dentists trained in these topics.

DENTAL OPTIONS

We no longer live in a time where dental metals are the only option for replacing teeth. Ask your dentist about using non-metal replace­ment options whenever possible. Non-metal options will vary, depending on what brands the office has available and what procedure is being done. Typical replacement options for fillings, crowns and implants will include forms of composites or porcelains. Speak with your dentist about which materials or brands are best for your particular situation.

There are situations, especially in some medical emergencies, where metals in the body may be extremely helpful and even life-saving. In such cases, try to get a metal allergy test so that if used, you can lower your risk of subsequent complications. You also can ask for non-metal options and discuss the pros and cons with your medical provider. If metal is placed, be sure to inquire whether it can be removed in the future and, if so, what that would entail. Sometimes, depending on your situation and the particular surgery, removing the metal later would be too risky.

My hope for dentistry is that it moves away from the use of dental metals and opts for non-metal options whenever possible. The European Union (EU) recently implemented some strict regulations pertaining to dental mercury, in particular, banning its use for certain groups⁷ and discussing the possibility of a complete ban in upcoming years.^13,36 This is very promising news. However, there are still many countries that use dental mercury, including the U.S. The FDA has only recommended against using amal­gam fillings for certain people but states that it does not support a ban of dental amalgam.¹² Hopefully, the FDA will change its mind and follow the EU’s lead.

Unfortunately, dental metals other than mercury are still commonly used. I hope that neurologists, physicians and other medical prac­titioners who treat patients with neurological conditions will become more aware of this issue.

POTENTIAL THERAPIES FOR NEURODEGENERATIVE CONDITIONS

In a promising case in the literature, a den­tist with Parkinson’s disease who was found to have mercury intoxication underwent chelation therapy, a process that helps remove metals from the body; after chelation, she regained her health.³⁷ Chelation therapy has been used successfully in many cases of PD—not only with mercury-related Parkinson’s symptoms but also with people who developed Parkinsonism after manganese exposure.^38,39 Although this work suggests that the combination of standard treatment, removal of dental amalgam fillings, chelation therapy and support for detoxification may be an optimal treatment for PD and other neurodegen­erative conditions, more research is needed.⁵ Therapeutic pharmaceutical approaches that help bind metals in the brain also have been explored for AD treatment.²³

The relationship between sleep, mercury and AD requires investiga­tion, but it is interesting to note that mercury accumulates in the pineal gland where melatonin is produced.^20,25 Preliminary research indicates that melatonin may be beneficial in addressing mercury issues in AD. Sleep issues and circadian rhythm disruption are strongly connected to PD as well.²⁰ Another AD study found that selenium and zinc may have a protective role against mercury toxicity.⁴⁰

FINAL THOUGHTS

Science says that we don’t know the definitive cause or causes of Parkinson’s, Alzheimer’s or ALS. However, there are clearly some striking relationships between metals, including dental metals, and these neurodegenerative conditions that warrant further investigation. Although we cannot say for sure which specific mechanisms are con­nected with specific diseases, given the evidence, it is clear to me that metal exposure is not something to be ignored when it comes to trying to figure out what is going on.

In the meantime, there has been some promising research on metals and neurodegenerative diseases with regards to metal removal, metal detoxification and improvement of neurological symptoms. Everyone’s body is different, and it is important to work with a practitioner who can help safely address your situation. More research needs to be done on these conditions and their relationship to dental metals, given that dental metals can be a significant contributor to metal toxicity.

REFERENCES

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This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly journal of the Weston A. Price Foundation, Fall 2024

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