the mold for later laboratory procedures. The wax pattern will undergo dimensional
changes with time so it should be invested as soon as possible. Investing, wax-
elimination, and casting are normally done by a dental prosthetic specialist. In a small
clinic having no dental prosthetic specialist, the dental officer or even the dental specialist
may perform these steps. These procedures are described in more detail in TC 8-226,
Dental Laboratory Specialist.
c. Indirect Method. This technique includes the making of an impression of an
individually prepared tooth and, in most cases, several adjacent and opposing teeth. An
individual tooth impression is usually made in a copper matrix band that has been
selected for size and adapted to the tooth. Either silicone or polysulfide base impression
material is normally used for an impression of an individual tooth. An impression of
several teeth is usually made in an impression tray with polysulfide base impression
material or reversible (agar) hydrocolloid. To secure maximum detail, the dental officer
normally uses special syringes, which the dental specialist has filled with the impression
material of choice, and ejects the material into the prepared areas.
d. Procedures for Impression Material.
(1) Reversible (agar) hydrocolloid. The dental specialist prepares the
impression material in strict accordance with the manufacturer's instructions and general
techniques discussed in Subcourse MD0502. When the material has been conditioned
for making the impression, the dental specialist passes the loaded syringe to the dental
officer who then fills the prepared area. While the dental officer accomplishes this step,
the dental specialist scrapes the water soaked outer layer of agar from the material in the
tray and passes it to the dental officer who makes the impression. The dental specialist
aids in the gelation of material by connecting one of the plastic tubes extending from the
tray to the tumbler water supply system and places the other tube in the cuspidor bowl.
The tumbler supply valve is then turned on, circulating the cool water through the tray and
gelling the hydrocolloid. After the impression is removed from the mouth, the dental
specialist should wash the saliva from its surface with cool tap water or cool slurry water
(solution of plaster of Paris or artificial stone and water). The dental specialist should take
precautions to avoid distortions or damage to the tissue and peripheral border areas of
the impression. He should make sure the impression is poured immediately to prevent
distortion of the impression, which would result in an inaccurate cast. In a dental clinic
that has no dental prosthetic specialist, the pouring of the cast may become the
responsibility of the dental specialist.