Dental amalgam is an alloy which results from mixing mercury with a silver tin alloy. This is used as a filling material in dental restorations. The term alloy refers to the combination of metals or a mix of one or more metals with other nonmetallic elements.
Skinner defines amalgam as a special type of alloy in which one of its constituents is mercury. In dentistry, both the terms amalgam and dental amalgam are used interchangeably.
History of Dental Amalgam
Amalgam was used for the first time in the United States in the year 1830. In the earlier days, the dentists used to file the silver coins and mix these filings with mercury. They then created a putty-like mix which was then placed in the defective tooth. But now the times have changed and the dental amalgam formulation has changed accordingly.
It is believed that the first use of amalgam was brought into practice by the Chinese. However, the modern day dental amalgam formula to counteract the problems of expansion associated with the alloy was developed by G.V.Black in 1895.
The formula for conventional low copper dental amalgam alloy is 67% silver, 27% tin, 5% copper, and 1% zinc. Today the alloy consists of silver (40%), tin (32%), copper (30%) and other metals.
Dental Amalgam Classification
I. According to the number of alloy metals used, the amalgam can be classified as :
1. Binary alloys which contain Silver and Tin.
2. Ternary alloys which contain Silver, Tin, and Copper
3. Quaternary alloys which contain Silver, Tin, Copper, and Indium.
II.According to whether the powder consists of unmixed alloys or admixed alloys.
Certain amalgam powders are made up of only one alloy. Few others have one or more alloys or metals that are physically added or are blended into the basic alloy like in the case of adding copper to a basic binary silver tin alloy.
III. According to the shape of the powdered particles used in the amalgam
1. Spherical shape type, which is the smoothly surfaced spheres.
2. Lathe cut type where the powder particles are irregular in shape and range from spindles to
3. The combination of spherical shaped alloys and lathe cut alloys (admixed).
IV. According to the size of the powder particle
2. Fine cut
3. Coarse cut
V. According to the Copper content in the powder
Low Copper content alloy where the copper content is less than 4% in the powder.
High Copper content alloy where the Copper content is more than 10% in the powder.
VI. According to the type of noble metal added to the alloy
VII. According to the changes in the composition of the Dental Amalgam alloy in the succeeding generations of Amalgam.
First generation amalgam:
This is the amalgam alloy formula given by G.V.Black where the alloy contains 3 parts of Silver and 1 part of Zinc.
Second generation amalgam alloys:
These amalgam alloys contain 3 parts silver, 1 part tin, 4% copper and 1 % zinc. 4% copper is used to decrease the plasticity of the mix and 1% Zinc is used to decrease the brittleness. Zinc is also used for its Oxygen Scavenger properties.
Third generation amalgam alloys:
These are a combination of First generation alloy and spherical amalgam alloy without the Copper eutectic alloy.
Fourth generation amalgam alloys:
In this type of amalgam alloy up to 29% of copper is added to original silver and tin powder which forms a ternary alloy. Here, the Tin binds with Copper.
Fifth generation amalgam alloys:
This is a quaternary alloy. This type of amalgam alloy contains Silver, Tin, Copper, and Indium.
Sixth generation alloys:
This type of dental amalgam alloy consists of the eutectic alloy.
VIII. According to the presence of Zinc
1.Zinc-containing alloys: These are the amalgam alloys that contain more than 0.01% of Zinc.
2. Non-Zinc Alloys: Amalgam alloys that contain less than 0.01% of Zinc.
Dental Amalgam Restorations
The main use of Amalgam is as a direct restorative material for insertion into a prepared tooth. Once hardened or set, Amalgam restores the tooth to the proper form and function.
There are mainly 2 types of Dental Amalgam restorations being used nowadays. Non bonded restorations and bonded restorations. Both these types of restorations require a certain type of tooth preparation design in which the Amalgam alloy will be later inserted.
This tooth preparation form or the cavity design in such a way that it removes all the defects in the tooth as well as all the weakened tooth structure. This cavity design also allows the Amalgam to function properly.
Are Amalgam Fillings Dangerous?
Because of the mercury content in the Amalgam people nowadays are worried about the potential health hazards. But FDA has recently announced that Amalgam fillings are not dangerous to your health unless you have an allergy to amalgam or other elements used in the amalgam alloy.
The mercury that is used in dental amalgam is elemental mercury, which means that amalgam releases low levels of mercury in the form of vapors. As this is very minimal, amalgam fillings are quite safe. FDA believes that amalgam fillings are safe in adults and children aged 6 and above.
Things to Remember Before Getting Amalgam Fillings
Although the dental amalgam fillings are considered relatively safe, there are certain things we need to remember before getting one.
- It is better to avoid these fillings if the individual is pregnant.
- If the person getting the filling done is allergic to mercury or is concerned about the mercury hazards, alternate filling
- materials can be used for tooth restorations.
Safety Measures For the Dentist and Dental Personnel
Even the dentist and the dental staff need to take necessary precautions while handling mercury.
The dental clinic where the amalgam alloy is being used should be well ventilated. Enough care should be taken not to spill any mercury while the manual mixing procedures. Proper isolation and safety gears like a face mask, eyeglasses, and high volume suction are a must when working on the patient using amalgam alloy.
Proper disposal of alloy waste has to be done. It is good to use amalgam separation devices which prevent the alloy from getting into the water supply.
When is Dental Amalgam Used?
Dental amalgam can be used in the following conditions.
- The prime use of amalgam is in the form of a restorative material, especially in Class I and class II teeth cavities.
- It is especially useful in restoring teeth with moderate to large cavities.
- The amalgam can also be used for core build up. It can also be used as a die material.
- When placing removable appliances in the mouth few teeth are used as abutments. In such teeth, dental amalgam may be used.
- Amalgam can also be used with composite resins in premolars and molars.
When Can Amalgam Be Not Used?
Because of the color of Amalgam, it is not used as an aesthetic restorative material which means it can’t be used in areas of teeth where aesthetics is of prime concern.
Because of the invent of composite restorations in later years, amalgam is no longer used while restoring small defects on molars and premolars and instead composite restorations are preferred.
Advantages of Dental Amalgam
Following are some of the important benefits of Amalgam material.
- It is very easy to use
- Amalgam has high tensile strength. Tensile strength is the resistance of a material to break under tension.
- Amalgam also has excellent resistance to wear.
- It is cheaper compared to composite and other tooth-colored restorations.
- Postoperative sensitivity is minimal in dental amalgam restorations
Properties of dental amalgam
Amalgam alloy has good compressive strength but poor tensile strength. Amalgam is brittle and tends to break if placed in thin layers. So it must be placed in bulk.
Newer alloys have lesser changes such as contraction or expansion on setting when handled well.
This is a property of a dental material which results in plastic deformation under occlusal load. Creep results in protrusion of the filling overtime resulting in overhanging and fractures of the filling. The high copper alloy has lesser creep compared to low copper alloy.
It is the process of gradual destruction materials especially metals. This destruction is caused due to the chemical or electrochemical reaction of the metal with the surrounding environment. Due to the structural configuration of the dental amalgam, it acts as an anode as well as a cathode and the surrounding saliva acts as the electrolyte triggering the process of corrosion.
This corrosion, however, is beneficial in the case of amalgam restorations as they tend to act as excellent sealants providing a perfect marginal seal for the fillings.
Seepage of oral fluids, food debris, and microorganisms through the microscopic space present between the filling and the prepared tooth surface is microleakage. In the case of amalgam, the corrosion products formed, seals the micro space and reduce microleakage.
This is a good thermal conductor. Hence the prepared tooth will need pulp protection in the form of varnishes, liners or bases.
The amount of vapor released by mercury is very minimal and the possibility of toxic reaction is less. The dentist needs to carefully handle mercury and follow disposal methods correctly to minimize the risk of mercury toxicity because of increased exposure to mercury on a regular basis.
Preparation of Dental Amalgam for Restorations
There are certain steps followed by the dentist while preparing the alloy of amalgam for restorations.
Isolation of the Tooth
Isolation of the prepared tooth is an important factor which affects the setting of dental amalgam. Use of matrix band and wedges and also rubber dam for moisture control is a good way to achieve isolation before packing the alloy into the tooth.
The prepared tooth will need a protective liner or a base below the amalgam filling to prevent post restorative sensitivity. Varnish may be used as a liner or there are types of cement like glass ionomer, zinc phosphate or zinc oxide eugenol which are used as bases.
The process of mixing the alloys with mercury is called trituration. This is done by the dentist or dental assistants mechanically in two ways.
- Correct proportions of mercury and alloy are put in an amalgamator(motorized) and the mixing takes place there. Earlier days the mixing was done manually using mortar and pestle.
- Pre encapsulated by the manufacturer, which is mixed in an automatic vibrator. This is the much safer and preferred method as the risk of mercury spillage is very unlikely.
This is carried out by hand instruments.The amalgam has to be placed in increments and packed well into the prepared tooth.
Pre Carve Burnishing
The prepared cavity is usually filled with excess amalgam material which is burnished using a burnisher.
This is done using hand instruments to incorporate the natural occlusal grooves and ridges of the tooth in the filling.
Post Carve Burnishing
This step is done to smoothen the edges. It also makes the surface of the filling shiny. This process also creates a good marginal seal between the tooth and the restoration, thus lowers the chances of microleakage.
Ideally polishing is done after 24 hrs of the restorative procedure. The filled amalgam needs a day to set well and attain good strength.
An Important Instruction
Individual who gets an amalgam filling done needs to be careful while eating. At least for a day, the tooth with the new amalgam filling shouldn’t be used to bite or chew anything hard.