Wide still of an amalgam tooth and a cracker, showing chewing as a mercury-vapor trigger, in the SMART frame.

Why this Lancet letter still anchors mercury-amalgam education

On 5 May 1979, The Lancet published a Letter to the Editor titled “CHEWING RELEASES MERCURY FROM FILLINGS.” The authors—Don D. Gay, Robert D. Cox, and John W. Reinhardt—wrote from the Departments of Preventive Medicine and Chemistry and the College of Dentistry at the University of Iowa. The letter occupies pages 985–986 of issue 8123—Lancet 1(8123):985–6 in the 1979 numbering, catalogued today as Volume 313. DOI: 10.1016/S0140-6736(79)91773-2. PubMed: PMID 87664, publication type Letter, MeSH including Mastication, Mercury / toxicity, and Mercury Poisoning / etiology.

That is the journal of record. IAOMT SMART materials cite it as Reference #5, often without printing the word Lancet. It is the same paper. IAOMT uses it for a specific protocol sentence: mercury vapour is released from dental amalgam fillings at higher rates during brushing, cleaning, clenching, chewing, and similar mechanical stimulation. Their title is the finding. Chewing releases mercury from fillings.

What they measured

The Iowa group was already examining “the exposure of dental patients to elemental mercury via dental restorations.” They noticed that chewing, after teeth had been filled with silver-mercury amalgam, raised the elemental mercury the patient breathed out—then measured that increase with silver-trap atomic absorption.

The patient expires ten times through a Drierite tube into a Vycor tube packed with 1 g of silver wool mesh. The trap, wrapped in nichrome wire, is later connected to a continuous-flow apparatus monitoring mercury at 254 nm; heating the wool releases adsorbed mercury into the monitor. The instrument is calibrated with standard concentrations of mercury injected onto the silver. After a background collection, the patient chews a piece of gum for 15 minutes and repeats the ten expirations. They published a table, “EFFECT OF CHEWING ON MERCURY IN EXPIRED BREATH,” and summarized it in the running text. The result below is that author summary.

What they found: chewing releases mercury

“We found that the level of elemental mercury in the expired breath of patients with silver-mercury amalgams up to 2 years old increased almost four times after a 15 min period of chewing (see table).”

Three control observations sit next to that rise:

  • Patients with no silver-mercury fillings had lower pre-chewing mercury than patients with fillings.
  • In the no-filling patients, mercury levels were not affected by chewing.
  • One patient with no fillings was also a heavy smoker, “yet no increase in mercury was observed.”

Chewing did not raise expired elemental mercury in mouths that lacked amalgam. Smoking, in the one no-filling smoker they flag, did not produce the rise. The increase tracked silver-mercury fillings after ordinary gum chewing—not after a dental drill—and the authors specify amalgams up to two years old. A so-called “silver” filling that has already sat in the mouth is still a mercury source, and chewing still drives that source.

Chronic exposure—and the methylation warning

The letter does not stop at the breath measurement. The authors cite Cross, Dale, Goolvard, Lenihan, and Smith (Lancet, 1978) on methyl mercury in the blood of dentists, at levels significantly greater than in a control group. They quote the Cross control range as 1.9–13.7 ng/g dry weight of blood and ask how many of those controls had silver-mercury amalgam fillings. Their closing sentence is a materials statement:

“Such amalgams give a low level, chronic exposure to elemental mercury with the real possibility of biotransformation to the more toxic methylmercury.”

That is the 1979 Iowa group, in The Lancet, describing dental amalgam as a chronic elemental-mercury exposure with a path to the more toxic organic form. PubMed’s MeSH tag—Mercury Poisoning / etiology—places the letter in the poisoning-etiology literature. WHO’s 2005 Mercury in Health Care paper later stated the same route in policy language: amalgam is typically about 45–55% mercury, and about 80% of inhaled mercury vapour is absorbed through the lungs. Gay’s method caught that vapour in expired breath. Chewing put more of it there.

Follow-up: expired air, blood, and urine

The letter’s footnote 3 points to related Iowa work then in press at the Journal of Dental Research (Reinhardt, Boyer, Gay, Cox, Svare, and Frank). The same mechanism reappears in the papers that followed.

Svare et al., J Dent Res 1981 (60(9):1668–1671)—same Iowa group, including Gay, Cox, and Reinhardt—analyzed expired air from 48 people (40 with amalgam, 8 without) before and after chewing. Amalgam subjects already had higher pre-chewing mercury. After chewing, levels increased an average of 15.6-fold in that group and remained unchanged without amalgam. Conclusion: in situ dental amalgams can increase the level of mercury in expired air.

Abraham, Svare, and Frank, J Dent Res 1984, measured blood and mouth-air mercury before and after chewing in 47 people with amalgam and 14 without. Mouth-air mercury rose with chewing only in the amalgam group. Blood mercury was positively correlated with the number and surface area of amalgam restorations and was significantly lower without amalgams. Sällsten et al., J Dent Res 1996 (IAOMT SMART Ref. #53), compared 18 habitual nicotine-gum users (median 10 pieces/day for 27 months) with 19 referents of similar amalgam-surface count. Plasma mercury was 27 nmol/L versus 4.9 nmol/L; urine mercury 6.5 versus 1.2 nmol/mmol creatinine. The authors: “The impact of excessive chewing on mercury levels was considerable.”

How this citation powers SMART education

Topic What Gay 1979 states How IAOMT SMART materials use it
Journal / form Lancet Letter, 5 May 1979; 1(8123):985–6 (also Vol. 313, issue 8123) SMART Reference #5 (journal name sometimes dropped in the short cite)
What is released Elemental mercury in expired breath Supports the claim that amalgam fillings emit mercury vapour
What raises the release 15 min of chewing gum → almost fourfold rise; amalgams up to 2 years old Cited for higher vapour rates during chewing, brushing, cleaning, clenching
What does not raise it No-filling patients: lower baseline; no chewing effect; one heavy smoker, no rise The source is the amalgam, not chewing or smoking as such
Chronic-dose language “Low level, chronic exposure to elemental mercury” with “real possibility” of conversion to methylmercury Sits with later SMART refs on stimulation, chewing gum, and systemic markers

The letter is a release-and-dose citation, not an operatory-equipment paper. It does not list rubber dams or respirators. What it does is take the “silver filling” story off the table. Amalgam in the mouth is a mercury source. Chewing makes that source deliver more elemental mercury into the air the patient expires.

Practical takeaways

  1. 1. The journal is The Lancet. Gay, Cox, and Reinhardt, 5 May 1979, Letter, 1(8123):985–6 (Volume 313 in the modern catalogue). DOI 10.1016/S0140-6736(79)91773-2. PMID 87664.
  2. 2. Chewing releases mercury from amalgam fillings. That is the authors’ title and their result: almost fourfold more elemental mercury in expired breath after 15 minutes of gum chewing, in patients with silver-mercury amalgams up to two years old.
  3. 3. No amalgam, no chewing rise. Patients without those fillings started lower and did not increase; a heavy smoker without fillings did not produce the signal.
  4. 4. The method is elemental mercury in expired breath—ten expirations onto silver wool, then 254 nm atomic absorption.
  5. 5. The authors call the exposure chronic and flag biotransformation to methylmercury as a real possibility.
  6. 6. Later papers enlarge the same fact: Svare 1981, a 15.6-fold expired-air increase after chewing; Abraham 1984, mouth air plus blood mercury that tracks amalgam load; Sällsten 1996, habitual gum chewing raising plasma and urine mercury. SMART cites Gay as Reference #5 for stimulated vapour release.

Bottom line

Gay, Cox, and Reinhardt’s 1979 Lancet letter is a short, instrumented clinical observation with a title that does the work: chewing releases mercury from fillings. Patients with silver-mercury amalgams up to two years old exhaled almost four times as much elemental mercury after fifteen minutes of gum chewing. Patients without those fillings did not. The authors described amalgam as a chronic elemental-mercury exposure with a real possibility of conversion to methylmercury. For thesmartchoice.com / IAOMT SMART education, Reference #5 is the early Lancet measurement that chewing—ordinary mechanical stimulation of a so-called silver filling—raises the mercury dose.

Citations

  1. 1. Gay DD, Cox RD, Reinhardt JW. Chewing releases mercury from fillings. Lancet. 1979 May 5;1(8123):985-6. Letter to the Editor. Also catalogued as The Lancet 313(8123):985-986 (5 May 1979). DOI: 10.1016/S0140-6736(79)91773-291773-2). PMID: 87664. Publisher: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(79)91773-2/fulltext
  2. 2. U.S. National Library of Medicine. PubMed PMID 87664 — publication type Letter; MeSH: Dental Materials / toxicity; Mastication; Mercury / toxicity; Mercury Poisoning / etiology. https://pubmed.ncbi.nlm.nih.gov/87664/
  3. 3. International Academy of Oral Medicine and Toxicology (IAOMT). The Safe Mercury Amalgam Removal Technique (SMART) (Ref. 5 = Gay 1979, used for higher mercury-vapour release during chewing / brushing / cleaning / clenching). https://iaomt.org/resources/safe-removal-amalgam-fillings/
  4. 4. Cross JD, Dale IM, Goolvard L, Lenihan JMA, Smith H. Methyl mercury in blood of dentists. Lancet. 1978 Aug 5;2(8084):312-3. DOI: 10.1016/S0140-6736(78)91711-791711-7). PMID: 79101. (Cited in Gay 1979; Gay quotes the control methylmercury range as 1.9–13.7 ng/g dry weight of blood.)
  5. 5. Svare CW, Peterson LC, Reinhardt JW, Boyer DB, Frank CW, Gay DD, Cox RD. The effect of dental amalgams on mercury levels in expired air. J Dent Res. 1981 Sep;60(9):1668-71. DOI: 10.1177/00220345810600090601. PMID: 6943160. (IAOMT SMART Reference #54.)
  6. 6. Abraham JE, Svare CW, Frank CW. The effect of dental amalgam restorations on blood mercury levels. J Dent Res. 1984 Jan;63(1):71-3. DOI: 10.1177/00220345840630011801.
  7. 7. Sällsten G, Thorén J, Barregård L, Schütz A, Skarping G. Long-term use of nicotine chewing gum and mercury exposure from dental amalgam fillings. J Dent Res. 1996;75(1):594-8. DOI: 10.1177/00220345960750011301. (IAOMT SMART Reference #53.)
  8. 8. World Health Organization. Mercury in Health Care: Policy Paper. Geneva: WHO; 2005. WHO/SDE/WSH/05.08. Typical amalgam mercury content ~45–55%; about 80% of inhaled mercury vapour absorbed through the lungs. https://www.who.int/docs/default-source/wash-documents/mercury-in-health-care.pdf

Source note: Findings, methods, and quotations are taken from the 1979 letter (recovered two-page Lancet text) and from published abstracts of the follow-up papers listed above. The chewing table is cited as the authors summarize it (almost four times after 15 min of chewing). Individual table-cell concentrations and the letter’s exact patient n were not recovered as readable running-text values and are not invented here.