1-6.
ADVANTAGES AND DISADVANTAGES OF AMALGAM
a. Advantages. Amalgam has many advantages over other materials as a
restorative material. Amalgam is used more than any other material to restore carious
teeth. It is easy to insert into the cavity preparation and adapts readily to cavity walls.
In obtaining its initial set, or hardness, amalgam allows time for condensing and carving.
It has an acceptable crushing strength and is recognized as having a long life as a
restoration. As an amalgam restoration ages in the oral cavity, corrosion products form
along the restoration-tooth interface. These compounds act as a mechanical block to
micro-leakage and account for the excellent clinical results obtained with silver
amalgam.
b. Disadvantages. Amalgam has many disadvantages as a restorative
material. Because amalgam's color does not match the color of the teeth, it is generally
not used on the visible surfaces of anterior teeth. Amalgam will tarnish with time, no
matter how well the amalgam restoration is prepared and inserted. To avoid or to
reduce tarnish, the restoration is smoothed and highly polished a day or two after its
insertion. The restoration may be repolished later at any time with little effort. Amalgam
will also conduct heat or cold readily (high thermal conductivity). If the amalgam is
placed too close to the pulp, it may irritate the pulp. Therefore, an intermediate base
that will not conduct heat or cold as readily (low thermal conductivity) is placed under
the amalgam.
1-7.
USAGE AND PREPARATION OF AMALGAM
a. General. The dental specialist has the direct responsibility for the correct
preparation and use of amalgam. Incorrect use may produce a faulty restoration that
can cause or contribute to the loss of a tooth. Therefore, the dental specialist must use
extreme care in preparing a good mix of amalgam that will provide the best qualities
obtainable from the alloy.
b. Trituration of Amalgam. Trituration, or amalgamation, is the mechanical
mixing of the alloy and mercury which, when mixed, forms the mass of amalgam
needed to restore the tooth. Trituration is done by a mechanical amalgamator (see
figure 1-2). Trituration is done by setting the timer according to the manufacturer's
instructions for the alloy and for the type amalgamator used. Special capsules are
furnished with the mechanical amalgamator to hold the alloy-mercury mixture during
trituration. Each capsule is preloaded with amalgam alloy and liquid mercury and a
small rod-like pestle that aids in the mixing process. The amalgamator mixes the
amalgam in the capsule by rapid shaking or vibration. This produces a consistently
uniform mix. The amalgamator reduces trituration to a matter of seconds. When the
time selected has elapsed, the automatic timer will stop the machine. The dental
specialist must be careful not to overtriturate or undertriturate. Overtrituration results in
shorter setting time and increased shrinkage. Undertrituration results in increased
expansion, lengthened setting time, and weakened amalgam.
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