The quantity of mercury has been reduced over time and newer and newer components are incorporated in the alloy powder to reduce the corrosion of dental amalgam in the oral cavity.
HISTORY
Louis Regnart added mercury to the D’Arcet’s Mineral Cement mixture, which was widely used in France then, lowering the temperature required to boil the mixture significantly, and for this became known as the ‘Father of Amalgam’. Early amalgam was made by mixing mercury with the filings of silver coins. Crawcour brothers (from France) introduced the amalgam in the United States of America in 1833 which used to have significant expansion which even caused tooth fractures in some restorations. However, this challenge was overcome when in 1895, GV Black developed a
formula (67% silver, 27% tin, 5% copper, 1% zinc) for modern amalgam alloy. Black’s formula overcame the expansion problems of the existing amalgam formulations.
APPLICATIONS
1. As a permanent filling material for
— Class I and class II cavities, and
— Class V cavities where aesthetics is not important.
2. In combination with retentive pins to restore a crown
3. For making dies
4. In retrograde root canal fillings
5. As a core material.
CLASSIFICATION OF AMALGAM ALLOYS
BASED ON COPPER CONTENT
Low copper alloys: Contain less than 6% copper (conventional alloys)
High copper alloys: Contain between 13-30% copper.
The high copper alloys are further classified as:
- Admixed or dispersion or blended alloys.
- Single composition or unicomposition alloys.
BASED ON ZINC CONTENT
Zinc-containing alloys: Contain more than 0.01% zinc
Zinc-free alloys: Contain less than 0.01% zinc
BASED ON SHAPE OF THE ALLOY PARTICLE
Lathe cut alloys (irregular shape)
Spherical alloys
Spheroidal alloys
BASED ON NUMBER OF ALLOYED METALS
Binary alloys, e.g., silver-tin
Ternary alloys, e.g., silver-tin-copper
Quaternary alloys, e.g., silver-tin-copper-indium.
BASED ON SIZE OF ALLOY
Micro-cut
Macro-cut
ADVANTAGES AND DISADVANTAGES OF AMALGAM RESTORATIONS
Advantages
1. Reasonably easy to insert.
2. Not overly technique sensitive.
3. Maintains anatomic form well.
4. Has adequate resistance to fracture.
5. After a period of time prevents marginal leakage.
6. Have reasonably long service life.
7. Cheaper than other alternative posterior restorative material like cast gold alloys.
Disadvantages
1. The color does not match tooth structure.
2. They are more brittle and can fracture if incorrectly placed.
3. They are subject to corrosion and galvanic action.
4. They eventually show marginal breakdown.
5. They do not bond to tooth structure.
6. A risk of mercury toxicity.