How To Manipulate Dental Amalgam?
PROPORTIONS OF ALLOY TO MERCURY
Correct proportioning of alloy and mercury is essential for forming a suitable mass of amalgam for placement in a prepared cavity. Some alloys require mercury – alloy ratios in excess of 1:1, whereas others use ratios of less than 1:1 with the percentage of mercury varying from 43% to 54%.
SIZE OF MIX
Manufacturers commonly supply capsules containing 400, 600, or 800 mg of alloy and the appropriate amount of mercury. For large size cavities capsules containing 1200 mg of ally are also available.
MIXING OF AMALGAM: (TRITURATION)
Trituration of the alloy with the mercury is normally carried out in a mechanical amalgamator. The efficiency of the machine will be influenced by:
1. Speed of the particular unit.
2. The length and type of “throw” of the capsule.
3. The presence of a pestle in the capsule.
4. Length of time of mixing.
Mechanical amalgamators are available in the following speeds:
Low speed: 32-3400 cpm.
Medium speed: 37-3800 cpm.
High speed: 40-4400 cpm.
Over-trituration
Alloy will be hot, hard to remove from the capsule, shiny wet and soft.
It is better to slightly over-triturate than to under triturate an amalgam since:
-Extended trituration may reduce plasticity
-Shorten working time and
-Increase final contraction.
Under-trituration
Alloy will be dry, dull and crumbly; will crumble if dropped from approx 30 cm.
Reduced tritutation may result in:
-Incomplete wetting of the surfaces of the alloy particles by mercury.
-A weak interface between the matrix (gamma1) and the particles.
-Lower strength.
-Increased porosity.
-A rougher surface.
-Increased corrosion.
-Loss of surface finish.
Normal Mix: Shiny appearance separates in a single mass from the capsule.
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