- Has relatively low cost.
- It exhibits reducing micro-leakage with time (high copper amalgams can take up to
2 years for a marginal seal to be produced, double the time for low copper amalgams,
but high copper amalgams are not as susceptible to corrosion phenomena and
resulting porosity and therefore retain their strength.) - It is less technique sensitive compared with other restorative materials.
It is still important to control moisture as excess moisture causes delayed expansion
particularly in zinc-containing alloys, and for this reason rubber dam should always
be used if possible.
Despite these good properties, amalgam has two main disadvantages (1) it is not
aesthetic and (2) it contains mercury, a known poison. Little can be done to combat
the poor aesthetics. Remembering to polish amalgams does improve characteristics,
including appearance and leads to a significant reduction in their replacement.
Clinicians concerned about the toxicity of silver amalgam seek re-assurance on the
continuing use of the alloy. There are four main areas of concern:
(1) Inhalation of mercury vapour or amalgam dust;
(2) The ingestion of amalgam;
(3) Allergy to mercury;
(4) Environmental considerations.
Inhalation of amalgam dust is most likely to occur during removal of a previous
restoration. This effect is transient and the effects minimized, if the operator uses
rubber dam and high speed aspiration. It is not in dispute that mercury is released
from amalgam restorations, during placement, polishing, chewing, and removal, but
the amounts are very small and come nowhere near the amounts ingested from other
daily sources, for example, air, water, and diet. True allergy to amalgam is rare. There
have been only 50 cases reported in 100 years. Many countries are trying to reduce all
industrial uses of mercury for environmental reasons and better mercury hygiene in
dental practice is one of the areas targeted.
In small occlusal restorations the only difference needed in the tooth preparation
between composite and amalgam is that when an amalgam is to be placed,
undermined enamel must be removed. In both cases a resin sealant material should be
placed over the margins of the restoration and the remaining fissure system.
Researchers report very high success rates when amalgam is used in this manner (451HFig.
9.21).
Composite resins
Many dentists advocate the use of composite as a restorative in the treatment of
children. Since their introduction in the 1970s, there have been many modifications.
Abrasive wear of many composite systems is comparable to that of silver amalgam in
the region of 10-20 um/year, and colour stability is now excellent compared with
earlier materials.