Cast materials are used to
take plaster casts of your teeth.
A plastic impression (mold) is filled with plaster, which provides a
dental technician with an accurate plaster model of your teeth. The
dental technician can thus form a dental prosthesis based on this model.
Cast materials should be able to flow easily and absorb moisture well –
thus allowing for a model which accurately delineates the structures to
be shaped. Accurate delineation is crucial in order to make the
prosthesis fit well. After a certain time, this material should also
harden quickly, but still allow for a long enough processing time.
Most of these materials consist of two components, which are mixed
directly before the process starts and then begin to harden. Earlier,
and even today (due to financial constraints), technicians used
self-mixing materials – such as alginate powder, which is activated by
water. As this makes it difficult to adhere to standard mixing ratios,
it could cause warping in the cast, resulting in a cast which does not
fit tightly.
The picture shows an extracted tooth with a crown, the dark spot on the
edge is a cavity. Enlarging the picture makes it easier to see the gap
between the tooth (creamy–beige) and the edge of the crown
(metallic–blue). The crown did not fit well, bacteria were able to lodge
inside the tooth and a cavity formed.
A quality cast is provided by ready-made cartridges, which involves more
material, but the components are mixed according to exact ratios, and
the technician receives more precise impressions, resulting in a
prosthesis with a better fit .
A quality prosthesis not only requires correct mixing and processing of
materials, however, what also counts is the length of time the cast
stays in the mouth of the patient, the packaging of the cast and
transportation to the technician, which should be carried out according
to manufacturer specifications – which is the only way to avoid warping.
Long transport distances and times – e.g. to China, do not make for
well-fitting work.