Recently I read an article by a paper in which it was noted that there was a “controversy” over the emission of Hg from amalgam. The paper noted research by Dr. Boyd Haley(1) indicating amalgam released large amounts of Hg over time(4-24 ug per cm2 per day on average). The article then quoted another researcher, who is funded by the dental materials industry who stated that there had been many papers published refuting Haley.
As an experiment I decided to randomly pull a research paper supposedly directly measuring Hg release from amalgam to see if it refuted Dr. Haley’s well known result of release of approximately 4-22 ug per filling/cm2 per day in the lab(1).
I located the paper “Mercury Release from Dental Amalgam, an in vitro study under controlled chewing and brushing in an artificial mouth” published in the Journal of Dental Research. The online version of the ariticle can be found at http://jdr.sagepub.com/content/74/5/1185.
Here is what I found. The paper starts out very scientifically. A device to simulate chewing is located in a sealed canister. Four holes are drilled in to accomodate different tubes, one for the mercury vapor analyzer, one for delivery of distilled water spray, and a fourth tube to remove water from the sealed environment and a nozzle is inserted into the canister to measure Hg vapor release. Supposedly air is drawn into the chamber, to simulate inhalation, while water spray simulates salivary action. Two teeth are attached to mechanical devices to simulate action of the jaw and one mercury filling was placed in the bottom tooth. I.E. one tooth with one amalgam is pressed against another to simulate chewing with a mechanical mechanism.
The first thing which jumps out at you is the comment pg (1187)
Immediately it is evident that the amalgam will be formulated in an almost ideal fashion, which does not reflect the many sloppy procedures used in the field, which include defective machinery, materials and poor condensation of the amalgam. So right away we see that the study is not intended to really measure the worst case scenario for patients. That’s ok though. Haley uses freshly aged amalgam.
The next thing which jumps out at you is the water spray used to simulate the action of saliva
pg(1186). States the author,
Evidently then, after spraying the amalgam with water spray, the water will be removed from the chamber from the fourth tube to remove water. But wait? Doesn’t that effectively wash any excess mercury liquid off the surface of the filling and deposit it effectively underwater on the bottom of the canister, where it is then removed by the fourth tube? Isn’t placing Hg underwater actually the preferred method of storage recommended by the ADA? The reason why this is important is because there is no reason to assume that sublimation is occurring (direct conversion of a solid to a gas). Likely is the formation of microscopic droplets on the surface of the amalgam in a liquid phase before conversion to a vapor. For if there was excess Hg on the filling coming off as a vapor the first thing I would do to get rid of it would be to blast it off with water spray and then remove the water containing this mercury from the tube. Surely this is some kind of misunderstanding, or it would not be used for most of the actually experiment but then on pg (1187) it is stated “A controlled spray of distilled water was injected onto the teeth..in pulsed mode during both chewing and brushing experiments”. Not to mention that most credible scientific experiments simulating saliva go to great pains to create a special chemical solution with the exact properties of saliva. So here we immediately have strike number 2.
Next as anyone knows any gas in a sealed container reaches an equilibrium. Because Hg coming off the filling really is a gas (and a liquid on the surface of the filling), measuring it in a sealed environment can actually reduce effective measurements of Hg vapor as anyone who learned the law PV=nRT should know. For example if you were to cover a small puddle with a glass, the puddle might not evaporate. But take the glass off the puddle and it quickly evaporates. This is true, even if air is periodically brought into the chamber. The Hg “saturates” the air.
Another analogy would be attempting to measure sugar diffusion from a sugar cube in a cup of coffee by completely dissolving the cube and supersaturating the coffee with sugar, then periodically scooping out some coffee with a table spoon, measuring the sugar concentration and putting in a table spoon of fresh water, “all the while continuing to dissolve more sugar”. This is like trying to periodically replace some of the air in the Hg saturated chamber and measure the Hg diffusing from the filling by taking small air samples. Clearly this is ludicrous and typically in the case of chemical diffusion great pain is taken to make sure that measurements in liquid occur, before any of the measured substance could diffuse beyond the point of measurement if the rate of diffusion or release of the substance is the desired measurement. Morever, the inside of the human mouth is covered with salivar, which itself could absorb Hg. Therefore the assumption that a similar equilibrium would be established in the human mouth is wrong.
Perhaps feeling a little sheepish themselves and realizing that taking such measurements would be transparently dishonest, (as if continuously spraying the surface of the filling with a water nozzle was not), the authors concede that measurement values are greatest when less time is given between measurements, before an equilibrium can be established. They then create a theoretical graph by which one can compute the effective release rate in ng/sec. Maximum values are reached as measurement time approaches zero, corresponding to real life Hg release. Pg (1187). This still does not solve the underlying problem with the physics of the situation, but it is somewhat better.
Here at last we have the scientific method at work. The authors now methodically take measurements both under chewing conditions and without, they even admit that there is huge variation under chewing evidently even with the water spray! (However while Haley notes a typical increase of Hg release with human brushing of the test amalgam of 10 times in his experiment, the clumsy brushing simulator used by the authors here only manages a slight increase in Hg release).
Now the final equation. To compute the total inhaled mercury the formula Ax60x8x.004x.8x.5 +Ax60x8x.58x.8x.5 + Ax60x8x.17x.8x.5 is used (pg 1188). A is given by interpolation of the graph at the value X=0, namely 1.5 ng/min. As noted above A is still no doubt greatly underestimated. But this still sounds good. We can see the rational for the equation. There are 3 terms for three 8 hour cycles, 60 minutes per hour. A quick calculation would give 3(8)60(A)=24(60)1.5×10-9=2160×10-9 grams =2 ug. In fact this is on the order of Haleys results (4-22 ug/day) and Haley gathers and analyzes all Hg given off by the amalgam, rather than washing the surface with a water spray or saturating the test device with Hg. Therefore we can easily account for a factor of 6. These results then seem surprisingly in agreement with Haley. And in fact this value for Hg release is charted in the paper which amounts to
But wait! (Is this too good to be true?)The final calculation of exposure is identical to this result but computed using the additional factors,.004,.5,.8. Where do these come from? These factors the authors explain “refer to retention of inspired mercury and the inspiration/expiration rate, respectively. Incredibley the .004 factor comes from an outdated 1940 study by Uddstromer as compared to recent ignored inhalation estimates provided by the EPA, indicating that “an individual at rest has .4% oral expiration”. .4% = .004 is approximately equal to zero. Therefore, all 3 terms in the final equation are multiplied by approximately zero! This definitely gives a whole new dimension to the argument “I didn’t inhale” and defeats the entire purpose of the experiment. Why measure the Hg release if we knew all along we weren’t really going to inhale it?
But we are not done yet! In the final table to add more insult to the scientific method the authors enter their results for 1 filling in a table with results for many fillings (Daily mercury estimates by Vimy and Lorscheider) by noting under footnote d “In vitro study presenting data from a single amalgam”. In vitro means, in the lab. In fact this is not a true in vitro study because the lab results were modified based on assumptions about what would happen in vivo. In vivo correspond with real measurments made in an actual biological system. How outrageous. Furthermore couldn’t they have scaled the result (which was already effectively multipled by zero, the “ inhalation factor”), instead of dividing by another unrelated factor of 10 before entering it in the table? Evidently no. Is this science? I think not.
Finally I’d like to point out that both Haley and this experiment only account for Hg emission from one side of the filling. In fact the surfaces of the filling inside the tooth will release mercury into the tooth which then gets absorbed by the jaw bone and can pass directly to the brain. If similar release rates occur on these surfaces all results would have to be multiplied by an additional large factor.
1 The relationship of the toxic effects of mercury to exacerbation of the medical condition classified
As Alzheimer’s disease,B.E. Haley,Medical Veritas 4(2007)1510-1524