Mahler DB, Adey JD, Fleming MA. Hg emission from dental amalgam as related to the amount of Sn in the Ag-Hg (γ1) phase. Journal of Dental Research. 1994;73(10):1663-1668.
Not every amalgam emits the same after abrasion. Mahler, Adey, and Fleming connected mercury vapor loss to tin dissolved in the silver–mercury (γ1) phase—explaining why freshly ground surfaces can spike vapor and why alloy chemistry still matters when films are stripped.
What the study found
Eleven commercial amalgams were selected whose gamma 1 phases contain different amounts of Sn. Amalgam specimens were ground on 600-grit carborundum paper and immediately placed into an apparatus designed around a gold film Hg vapor detector. Hg vapor loss in air over a 30-minute period was determined, and the log10 Hg loss/volume fraction gamma 1 was plotted vs. the Sn content of the gamma 1 phase for the 11 test amalgams. A linear regression of these data, showing that of the higher the Sn content in gamma 1, the lower the Hg vapor loss, produced a highly significant R2 = 0.94 (p < 0.001). To examine for differences in vapor pressure among alloys, we eliminated the oxidation effect by conducting these same tests in an argon atmosphere. Although the Hg loss was significantly greater in argon than in air, the same differences among alloys were observed. Thus, from the standpoint of both vapor pressure and oxidation, the amount of Sn in the gamma 1 phase of dental amalgam has a significant and specific influence on the potential for Hg vapor emission.
Why it matters for SMART
High-speed removal abrades passivating oxide films and creates hot particulate—Mahler’s experimental world in clinical form. Later authors have noted that some modern high-copper alloys can emit more vapor after abrasion than older low-copper types, consistent with lower tin in γ1. SMART does not gamble on brand chemistry mid-procedure: water, HVE, chunking, and mercury-rated respirators address the shared physics of fresh surfaces.
Practical takeaways
- Freshly cut amalgam is a vapor source—treat it as such.
- Higher Sn in γ1 meant lower Hg loss in this 11-alloy model (R²=0.94).
- Argon tests showed alloy ranking persists beyond oxidation films.
- Chunk rather than pulverize to limit abraded area.
- Full SMART PPE remains mandatory regardless of alloy lore.
Bottom line: Mahler et al. showed post-abrasion mercury vapor tracks tin in the γ1 phase—materials evidence that SMART must control emissions whenever amalgam is cut.
