RPD Manual 11 - Removable Prosthodontics - Dalhousie University

Jaw Relations, Altered Cast Technique and Wax Try-in - 91
7. The denture is placed intraorally to assess occlusion, vertical dimension, esthetics,
phonetics, and comfort.
8. A laboratory prescription form (for acrylic processing) and the articulator with mounted
models are sent to the laboratory for processing.
Altered Cast Impressions
Since frameworks made from master casts must be adjusted to fit intraorally, the relationship of
the teeth and denture base can change from that observed on the master cast. In tooth-borne
partial dentures this small change is negligible since the teeth provide almost the entire support
for the denture. In distal extension cases, however, the change can produce deleterious effects
on the supporting residual ridge and/or teeth, since the load must be distributed between the two
tissues. For this reason, a new impression (altered cast impression) is made with the partial
denture framework (after intraoral adjustment) so as to capture an accurate relation between the
teeth, framework and residual ridge.
Tooth and Tissue-Borne Removable Partial Dentures
Since the relationship of the framework to the soft tissues may change in a tissue-borne partial
denture, it is necessary to re-relate the framework to the supporting mucosa. This is
accomplished by attaching a small custom tray over the meshwork of the edentulous ridge, by
border molding the tray for proper extension and then making a new impression of the residual
ridge. The steps in this procedure are as follows:
1. The tentative outline of the denture base is drawn on the master cast with the framework in
place. This will permit greater accuracy in tray extension.
2. Remove the framework and place one thickness of baseplate wax spacer over the
edentulous ridge.
3. Grasp the framework with a hemostat or similar instrument and heat the meshwork over a
flame. While the framework is still hot, replace it over the master cast. Press to place with
a mirror handle, paper towels etc. to ensure you do not burn yourself. It is extremely
important that the framework fully seat at this stage. If it does not, the wax will prevent
full seating of the framework at the border molding, and possibly, the impression stage.
This would produce exactly the opposite effect that we wish to obtain (i.e. it would impair
the framework/tissue relation rather than improve it). To ensure the framework is fully
seated inspect it for the following:
a. tissue stop(s) should be entirely through the spacer(s)
b. the metal in region 1.5 -2 mm adjacent to the edentulous span should be entirely
through the spacer(s)
c. there should be no resistance felt as mesh melts through wax
d. rests should be fully seated in their rest seats
4. With a #7 wax spatula, remove wax from 6-7 of the holes in the meshwork. Leave
meshwork slightly undercut so acrylic tray can lock onto it.