Mercury in Dental Amalgam: Quantitative and Toxicological Summary

1. Mercury Content in Amalgam Fillings

Average amalgam filling weighs 0.31 grams.
Typically contains ~50% mercury by weight.
Mercury per filling: 0.155 grams (155 mg).

2. Vaporization Rate of Mercury in the Oral Environment

Assuming a cube-shaped filling (one side exposed), surface area ≈ 0.050 cm².
Estimated evaporation rate at 37°C: 0.02 mg/cm²/hr.
Per minute emission: 0.000017 mg/min = 17 nanograms/min.

3. Mercury Atom Count in Vaporized Quantity

17 ng mercury ≈ 8.47×10⁻¹¹ mol.
Total atoms: 5.1 × 10¹³ mercury atoms.

4. Time Estimates for Mercury Loss

Scenario	Time
1/100 of mercury vaporized (1.55 mg)	~63 days (0.17 years)
All 0.155 g mercury vaporized	~17.3 years

5. Replacement Criteria for Amalgam Fillings

Marginal breakdown or leakage.
Recurrent decay beneath or around the filling.
Fracture or chipping of filling or tooth.
Visible corrosion, discoloration, or loss of mechanical function.

6. Changes in Amalgam Composition Over Time

Amalgam undergoes surface corrosion and phase transitions.
Mercury remains largely chemically bound in stable intermetallic compounds.
Only minor mercury loss occurs over 15 years (~1–5 mg total), not substantially changing the mercury percentage.

7. Reassessing “Negligible” Mercury Loss

Loss of a few mg of mercury may seem small by mass, but is significant toxicologically.
Estimated daily exposure from 1 filling: ~24.5 µg/day.
This can meet or exceed EPA chronic exposure limits (0.3 µg/kg/day).

Revised Criteria for Substantial Mercury Loss

Criterion	Threshold for Concern
Total loss exceeds 1 mg	Yes – potentially systemically absorbed
Daily exposure exceeds 5 µg	Yes – may exceed reference doses
Observed neurological or renal biomarkers	Yes – medical action warranted
Structural damage or aesthetic need	Yes – dental replacement recommended

Conclusion

While amalgam mercury loss over time may be small by weight, its cumulative health implications can be substantial given mercury’s toxicity at low doses. It is essential to frame evaluations of mercury exposure from amalgams using toxicological safety thresholds rather than just material degradation metrics.