RPD Manual 11 - Removable Prosthodontics - Dalhousie University

Clinical Protocol, Final Impressions - 82
will result in an unacceptable master cast. Additionally, soft tissues should be healthy with no
evidence of inflammation or ulceration. All initial therapy should be completed.
Teeth and soft tissues should be dried for final impressions. Light-bodied impression material
should be syringed around the abutment teeth ensuring proper coverage of guiding planes, rest
seats and retentive areas. Trays should be loaded with light- or regular-bodied polysulfide
material. Increased filler content of medium body material will cause less shrinkage of the
material during
polymerization, and the use of these viscosities will cause less displacement of soft tissues than
high viscosity materials.
The tray should not be over-filled since gross excess will distend the soft tissues, resulting in an
inaccurate impression. Large embrasures or bridge pontics may be blocked out with orthodontic
wax using care to avoid placement on occluding surfaces or near abutments. This will make
removal of the impression easier, and minimize possible distortions of the impression. Practice
inserting and removing the tray prior to making the impression.
Evaluating the Impression
Final impression should meet the following criteria:
" No voids on any area where direct or indirect retainer will contact an abutment (rest
seats)
" No large voids under major connectors, minor connectors, infrabulge arms
" No significant tears, material not separated from the tray
" Peripheries well defined
" Accurately records available supporting tissues
" Allows for all elements of design
" No significant areas of “burn through” – areas where the border molding is not covered
and the tissues have been displaced
In the mandible, ensure the floor of the mouth and lingual frenum has been accurately recorded
to allow for major connector placement. An easy means to ensure non-encroachment on these
structures is to measure from the free gingival margin of 3-4 teeth to floor of mouth when the
tongue has been activated. Record and transfer these measurements to the master cast – the
inferior framework border should not be placed above this level
All critical anatomy should be recorded:
Vestibular depths recorded accurately
Hamular notches (marked)
Vibrating line (marked)
Retromolar pads
Frenal attachments
Floor of mouth (measured)
It is helpful to mark the vibrating line prior to making an impression because partially edentulous
impressions cannot be reseated over the teeth to determine this critical landmark, after removal
from the mouth, since the impression will not fully or properly seat over tooth undercuts.