2-19. INTERMEDIATE RESTORATIVE MATERIAL RESTORATIONS
If a matrix is required for intermediate restorative material (IRM), the preceding
materials and rules for amalgam restorations may be applied for it also. Intermediate
restorative material is the restorative material used in most temporary restorative
procedure cases. The IRM will be mixed on a parchment pad with a stainless steel
spatula. The techniques and standards for mixing IRM have already been discussed in a
previous subcourse. After the assistant has mixed the materials, the dental officer will
place it in the preparation with the cement plugger of his choice. Intermediate restorative
material is finished with the same instruments used to finish amalgam restorations.
2-20. GOLD ALLOY INLAYS (CROWNS)
a. Wax Pattern Procedures: General. In making a gold alloy inlay or crown, the
dental officer first prepares the tooth to receive the restoration. The next step is obtaining
a wax pattern. A wax pattern is an exact duplicate in wax of what is desired in the
finished restoration. Most wax patterns will be used to form a mold into which melted gold
alloy is cast to form the inlay or crown. Wax patterns are used also in the formation of
acrylic resin crowns. Wax patterns may be obtained by either of two methods. The direct
method is one in which softened inlay wax is applied directly to the prepared tooth and
carved to shape directly in the mouth. The indirect method is one in which an accurate
impression is made of the prepared tooth and adjacent teeth, the impression is poured to
provide a cast of these teeth, and the wax pattern is developed on the cast. Ways in
which the dental specialist may assist vary with the dental officer and the technique
followed.
b. Direct Method. In some classes of cavities, the dental officer may use a
matrix to replace the missing walls of the cavity to help confine and shape the wax when it
is forced into place. The matrix is lubricated so that wax will not stick to it and distort the
pattern. When the matrix is in place, the dental officer will soften a piece of wax in the
flame or warm water and then force it into place in the cavity. In making a crown or for
some inlay techniques, a copper band may be fitted to the tooth, filled with softened wax,
and forced into place upon the tooth carrying the wax into all areas of the preparation.
After the wax has been allowed to cool, it is shaped and carved, using wax spatulas and
carvers, to approximate the anatomy and outline desired in the final restoration. The
matrix material or band is removed some time before final finishing of the wax pattern.
When carving is completed and the pattern is to be used to produce a cast gold alloy
restoration, a sprue is attached to the wax pattern by heating the sprue metal, placing it in
contact with the pattern, and permitting the wax to harden around it. After the wax pattern
is withdrawn from the tooth, the free end of the sprue is inserted into a sprue former. A
sprue usually is in the form of a straight piece of metal. A sprue former is a cone-shaped
device of rubber or metal. The sprue and crater former are used to support the wax
pattern during subsequent procedures in which the pattern is invested in a plaster-like
casting investment to form a mold. The sprue and sprue former also form a passage into
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