What the Textbooks say about your health and Dental Amalgam
The following excerpts are copied directly from the widely used textbook Phillips Science of Dental Materials Tenth edition, W.B. Saunders C0. pp 83-84 and pp 403-404. This material is included to help allay the fears of patients who have been alarmed by the allegations of anti-amalgamists and health faddists who advocate the removal of all amalgam dental fillings.
This is quoted directly from a disinterested, scientifically respected source. This textbook contains over 700 pages. The material that follows was gleaned from only four of them. This source is a general textbook on materials science who’s main emphasis is NOT to refute the claims of anti-amalgamists. The emphases on this page (in boldface) were added by me.
The following is a table of the units of measure used in this discussion of mercury
Clarification: The term “ng” refers to nanograms, or billionths of a gram. It almost always refers to the level of mercury found in a milliliter of blood or serum.The term “μg” refers to micrograms, or one millionth of a gram. It generally refers to the level of mercury inhaled or ingested into the body.
For many years a controversy has raged over the biocompatibility of amalgam restorations because of the presence of elemental mercury. Another form that has received attention is methyl mercury that is contained in ocean fish. Methyl mercury is generally formed by biologic action on elemental mercury.
The Minamata disaster of the early 1970s in Japan was the result of the release of large amounts of inorganic (elemental) mercury in effluent from factories into local rivers. This mercury subsequently underwent methylation by bottom-dwelling organisms in the Minamata Bay of Japan. This methylated mercury accumulated, and was concentrated in the food chain, and humans were poisoned by eating contaminated fish and shellfish. This incident created quite a stir worldwide, and measurement of mercury in all forms of fish became a focal point for environmental scientists. Later, however, scientists found that fish from uncontaminated ocean waters, particularly tuna and swordfish, had high concentrations of methyl mercury in their tissues. This mercury is derived from areas of undersea volcanic activity and hydrothermal waters. Mercury accumulates in the food chain, and large cold-water fish have concentrations that often exceed FDA limits, even though the mercury is from natural sources. Virtually 100% of methyl mercury is absorbed in the gut. Thus, conversion of elemental mercury to methyl mercury would greatly increase absorption via the gastrointestinal route. This point is moot, however, because all the mercury in seafood is methyl mercury, and all is absorbed. The average contribution of one seafood meal per week to blood mercury levels of methyl mercury is many times that of the average contribution of elemental mercury from the presence of 8 to 10 amalgam restorations in the mouth.
[Note: All mercury ingested from dental amalgam is in the form of elemental mercury, while all of the mercury ingested from seafood is in the form of methylated mercury. The importance of this distinction lies in the relative solubility of each form. Elemental mercury is not very soluble and is therefore not well absorbed via the stomach and intestines, while the methylated form from seafood is well absorbed via this route…..MS]
Less than 0.01% of elemental mercury ingested via the stomach is absorbed. However, it does have a high vapor pressure. Between 65% and 85% of the mercury vapor that is inhaled is retained in the body; therefore, this route is of concern in considering the contribution of mercury absorption from dental amalgam. [See clarification of this point below….MS]
Much of the confusion associated with the biocompatibility of amalgam stems from ignorance of the signs and symptoms of mercury poisoning. Headache, one of the symptoms most frequently claimed to disappear on removal of amalgams, is not a symptom of mercury poisoning. The recognized symptoms of chronic mercury poisoning include weakness, fatigue, anorexia, weight loss, insomnia, irritability, shyness, dizziness, and tremors in the extremities. These signs and symptoms of methyl mercury poisoning [the symptoms mentioned above….MS] are distinctly different from those of elemental mercury poisoning which include the following: paresthesia [burning or tingling] of the extremities, lips, and tongue; ataxia (gait disturbances); and concentric constriction of visual fields (“tunnel vision”). [Note: all mercury absorbed into the stomach from amalgam fillings is of the elemental variety. (MS)]
When the most recent wave of anti-amalgam sentiment began, the claim was made that a few patients can react to extremely small amounts of mercury with the signs and symptoms of mercury poisoning, multiple sclerosis, epilepsy, and other diseases of unknown causes. It was alleged that these patients had a condition that prompted some dentists to diagnose this “micromercurialism hypersensitivity” through the use of the cutaneous patch test.
In spite of attempts to demonstrate a direct relationship between the presence of dental amalgams and elevated blood levels of mercury, none has been found. The average mercury level in the blood of subjects with amalgams was 0.7 ng/ mL (ng=billionths of a gram) (coefficient of variation = 78%), whereas the level in subjects without amalgams was 0.3 ng/mL (billionths of a gram-coefficient of variation = 77%). In comparison, other investigators reported that ingestion of one saltwater seafood meal per week raised the average blood mercury level from 2.3 to 5.1 ng/mL. Thus, one saltwater seafood meal per week can be expected to contribute seven times more mercury to blood levels than the presence of multiple dental amalgam restorations. The lowest level of total blood mercury at which the earliest nonspecific symptoms occur is 35 ng/mL (after long-term exposures). Thus, the widespread removal of amalgams is unwarranted.
The most significant contribution to mercury assimilation from dental amalgam is via the vapor phase. The patient’s encounter with mercury vapor during insertion of the restoration is brief, and the total amount of mercury vapor released during function is far below the “no effect” level. The most reliable estimates suggest that mercury from dental amalgam does not contribute a significant amount to the total exposure of patients. The results of one study in which patients with amalgam restorations were monitored with mercury vapor detectors over a 24-hour period showed that the amount of vapor inhaled was 1.7 µg/day [millionths of a gram] . Three other studies have confirmed that the magnitude of vapor exposure for a patient with 8 to 10 amalgam restorations is in the range of 1.1 to 4.4 µg/day. The threshold value for workers in the mercury industry is 350 to 500 µg/day, depending on activity level, and is based on an exposure of 40 hours per week. [Note that these measurements are in “micrograms” of mercury found as inhaled vapor. This is in contrast to the “nanogram” units discussed above which relate to the amount of mercury found in blood serum…MS]
Mercury blood levels that were measured in one study indicated that the average level in patients with amalgam was 0.7 ng/ml [billionths of a gram] compared with a value of 0.3 ng/mL for subjects with no amalgam. This difference was found to be statistically significant (P0.01). However, one should be aware of a study in Sweden that demonstrated that one saltwater seafood meal per week raised average blood levels of mercury from 2.3 to 5.1 ng/mL, a sevenfold increase (2.8 ng/mL) compared with that (0.4 ng/mL) associated with amalgam restorations. The normal daily intake of mercury is 15 µg from food, 1 µg from air, and 0.4 µg from water.
Quoted from Phillips Science of Dental Materials Tenth edition, W.B. Saunders C0. pp 83-84 and pp 403-404.
References and suggested reading cited in the textbook:
Berglund A: Estimation of a 24-hour study of the daily dose of intra-oral mercury vapor inhaled after release from dental amalgam. J Dent Res 69:1646, 1990.
A pioneering study conducted by measuring the intraoral vapor levels over a 24-hour period in patients with at least nine amalgam restorations. The average daily dose of inhaled mercury vapor was 1.7 µg (range from 0.4 to 4.4 µg), which is approximately 1% of the threshold limit value of 300 to 500 µg/day established by the World Health Organization, based on a maximum allowable environmental level of 50 µg/day in the workplace.
Eames WB: Preparation and condensation of amalgam with a low mercury:alloy ratio. I Am Dent Assoc 58:78, 1959.
This technique revolutionized the procedure in constructing an amalgam restoration by use of minimal amounts of mercury in the original mix
Fédération Dentaire Internationale: Technical Report 33: Safety of dental amalgam. hit Dent 39:217, 1989.
This authoritative organization reviewed the literature on mercury toxicity and concluded that there is no documented scientific evidence to show adverse effects from mercury in amalgam restorations except in rare cases of mercury hypersensitivity.
Mackert JR Jr: Factors affecting estimation of dental amalgam mercury exposure from measurements of mercury vapor levels in intra-oral and expired air. J Dent Res 66:1775, 1987.
This analytical study demonstrates that a previous paper on vapor release based on animal models was flawed and that the investigators in this previous study overestimated the daily dose by a factor of 16 or more.
Marshall GW, Marshall SJ, and Letzel H: Mercury content of amalgam restorations. Gen Dent November-December:473, 1989.
Amalgam restorations removed after prolonged clinical use contained nearly all the original mercury present, suggesting that mercury loss contributes only a minor amount to total daily dosage.
Mjor IA: The safe and effective use of dental amalgam. Int Dent J 37:147, 1987.
Many pertinent matters related to the amalgam restoration are discussed in this review, including mercury toxicity, longevity of the restoration, common causes for failure, and certain properties that relate to performance.
Powell LV, Johnson GH, and Bales DJ: Effect of admixed indium on mercury vapor release from dental amalgam. J Dent Res 68:1231, 1989.
Addition of indium decreased the release of mercury by reducing the amount of mercury required to wet the, alloy particle.
Rogers KD: Status of scrap (recyclable) dental amalgams as environmental health hazards or toxic substances. J Am Dent Assoc 119:159, 1989.
A review presenting available evidence to show amalgam scrap is not a toxic substance or environmental health hazard. It also covers portions of the literature indicating that intraoral amalgams do not present an adverse health hazard.
The consumer reports article was published in the May 1991 issue of Consumer reports monthly magazine. You may obtain this very informative article by writing to Consumers Union of the United States, inc. Yonkers, NY 10703