(2) Polysulfide base impression material. The dental specialist prepares the
impression material according to the manufacturer's instructions and general techniques
discussed in Subcourse MD0502. Normally, a double-mix technique is used. The dental
specialist mixes the syringe material, loads the syringe, and passes it to the dental officer.
While the dental officer is injecting the material into the prepared area, the dental
specialist mixes the heavy- or medium-bodied material and loads the customized tray.
The dental specialist receives the syringe with one hand and passes the loaded tray to
the dental officer who makes the impression. When the impression is removed from the
mouth, the dental specialist washes saliva from the surface with cool tap water or cool
slurry water. Dimensional stability is greater in polysulfide base impression material than
in the hydrocolloid impression materials. However, the dental specialist should make
sure that the impression is poured within one hour. Pouring the cast may become the
responsibility of the dental specialist when no dental prosthetic specialists are assigned to
e. Laboratory Procedures. Various types of casts are made from these
impressions. These include master casts with removable dies (model of the individual
tooth), split casts, and other types. The master cast is made of artificial stone while the
dies may be made of "die" stone, electroplated metal, or (sometimes) amalgam. Wax
patterns are made on the dies. The cast formed from an impression of the opposing
teeth are used to establish occlusal relationship. The master cast is used to establish
proximal relationships between the wax pattern and other teeth. Many dental officers will
have the patient return for a "try-in" of the wax pattern before it is sprued and invested.
Laboratory procedures involved are described in TC 8-226, Dental Laboratory Specialist.
f. Finishing and Cementing Cast Gold Alloy Restorations.
(1) General. When gold alloy crowns and inlays have been cast and
removed from the investment, they are ready to be carried to place in or on the prepared
tooth where they receive final fitting and polishing.
(2) Technique. The sprue may be cut from the casting before it is placed in
the prepared cavity or it may be left in place to aid in handling the casting, then cut off
later. Often, a few taps with the mallet and orangewood stick are needed to carry the
casting to place. Sometimes a small "bubble" of gold on the inner surface of the casting
keeps the casting from going into place and must be removed. Initial steps in fitting and
finishing the casting include adjustment of occlusion, removal of excess material from
margins and contours, refining occlusal anatomy, and establishing proper contacts with
adjacent teeth. Occasionally, it is necessary to build up contact areas by the addition of a
small amount of gold solder. When these finishing procedures are completed, the
restoration is smoothed and polished. When ready for cementing, both the tooth and
restoration are thoroughly cleaned and dried, the tooth is isolated with cotton rolls,
copalite varnish is applied, zinc phosphate cement (loose mix) is prepared, the cement is
applied to the tooth surface of the restoration, and the restoration is carried to the tooth
and tapped firmly in place using the mallet and orangewood stick. The restoration is held
in place with firm biting or other pressure until the cement has reached its initial set.