(2) Final impressions. The final impression is used to produce the master
cast upon which the denture is fabricated. The tray used for final impressions is made
of an acrylic resin material that is custom-made on the cast produced from the
preliminary impressions. This tray is adjusted to the patient's mouth by selective
grinding. The borders are molded with modeling plastic to clearly define the soft tissue
border and other landmarks, such as muscle attachments, frenum, and posterior palatal
seal area. The molded tray is used to carry the final impression material, a rubber-base
(polysulfide base) material, or a zinc oxide and eugenol paste (metallic oxide
impression) material, to place in the mouth. This impression should include the denture
supporting area and the denture border area. Figure 5-12 depicts instruments and
materials used for final impressions.
Figure 5-12. Instruments and materials for final impressions for complete dentures.
(3) Specific duties of the dental specialist. The dental specialist has specific
duties in regard to the preparation of complete dentures. The dental specialist:
(a) Prepares the impression material according to the manufacturer's
instructions and the techniques discussed in Subcourse MD0502, Dental Clinical
Materials, and fills the impression tray.
(b) Coats the patient's lips and surrounding area with petrolatum before
impressions are made to facilitate the removal of impression material.