Stone ME, Cohen ME, Berry DL, Ragain JC Jr. Design and evaluation of a filter-based chairside amalgam separation system. Science of the Total Environment. 2008 Jun 15;396(1):28-33.
When amalgam is placed or removed, mercury-bearing particles ride the vacuum line toward the sewer. U.S. Navy dental researchers designed a chairside filter system—capture at the chair, before debris travels deep into plumbing—and tested it in real operatories plus under the ISO amalgam-separator protocol.
What the study found
Prototypes used reusable chambers with disposable filters installed in five dental operatories. Configurations: 50 µm, 15 µm, 1 m, 0.5 µm, or no filter (control). Daily wastewater was collected for ten consecutive days per setup (Latin-square rotation; n = 50 samples per configuration). Mercury was measured by cold-vapor AAS (USEPA 7470A). Surfaces of amalgam placed and removed were tracked. Vacuum at the HVE tip was checked with 0.5 µm filters in place. The 0.5 µm and 15 µm setups were also run through ISO 11143.
Mean Hg per chair per day:
- No filter: 1087.38 mg (SD 993.92)
- 50 µm: 79.13 mg → 92.7% removal
- 15 m: 23.55 mg → 97.8%
- 1 µm: 17.68 mg → 98.4%
- 0.5 µm: 4.25 mg 99.6%
Filter-group differences were significant (ANCOVA P < 0.0001); the 0.5 µm filter removed more mercury than the 50 m and 15 µm filters. Vacuum dipped only minimally at install, then fell gradually as filters loaded. The 0.5 µm configuration passed ISO 11143 at 96.8% efficiency.
[Publisher paywall: Elsevier full PDF may require institutional access; quantitative results above are from the PubMed abstract / EPA HERO record.]
Why it matters for SMART
SMART protects people in the chair; separators and chairside filters protect the water pathway. Capturing amalgam at the chair also shields downstream plumbing from debris that can later release mercury. The Navy data show that pore size and maintenance (clogging → vacuum loss) decide real performance—echoing the broader lesson that certified hardware only works when serviced. Pair SMART chairside technique with a maintained separator/filter chain for a complete mercury-safety system.
Practical takeaways
- Capture early — Chairside filtration cuts Hg before it enters shared vacuum lines.
- Finer filters caught more — In this trial, 0.5 µm reached 99.6% clinical removal and 96.8% ISO efficiency.
- Watch vacuum — Loading slowly reduces HVE performance; replace filters on schedule.
- Track amalgam workload — Surfaces removed were a significant covariatebusy removal days load filters faster.
- Combine with SMART — Filters manage wastewater; they do not replace dams, suction, water, and PPE.
Bottom line: Stone and colleagues showed a simple chairside filter—especially at 0.5 mcan remove well over 95% of particulate mercury from dental wastewater while remaining clinically usable, reinforcing SMART’s environmental half of safer amalgam care.