Impressions for replica dentures Flashcards
Why must a replica block have a hard base? How is this achieved?
- For recording the master impression.
- Use of a SHELLAC base.
3 methods that can be used to “incase” the denture so that primary replica impressions can be taken.
- soap box.
- replication flask.
- Self-supporting putty in disposable impression trays.
Which surface do we take an impression of first for replica technique?
The POLISHED surface (teeth).
2 things that must be done prior to taking the FIT surface impression for a replica primary impression.
- Cut notches (reconneck like jigsaw).
- Apply separating medium (vaseline).
What can be used to correct small air blows/ blows?
PERFECTING PASTE (2 products - equal parts of each).
What are sprue holes?
- In replica technique, sprue holes are cut into the putty of the impression representing the “polished surface”.
- Allow wax to be poured in to form the replica block.
Shellac is brittle. What can be done to prevent this from breaking?
Addition of wire strengthener.
How short of the border of the base should the shellac be? Why?
- 1mm short.
Allows for WAX RIM:
- More comfortable.
- Easier to correct over/ under extension.
You are using replica technique however the denture is UNDERextended. How can this be fixed and what is the most appropriate time to do this?
- Addition of GREENSTICK. (heat, mold to denture, apply vaseline, check in mouth to see if problem corrected).
- Do this BEFORE TAKING PRIMARY IMPRESSION. (better special tray - saves chairside adjustment).
At what stage in the replica technique do we correct an underextended denture?
- BEFORE PRIMARY IMPRESSION (produces corrected special tray).
What is the issue of taking a replica impression of a metal palate?
- Chromium is thinner than wax and shellac.
- Would not have space for shellac/ replica block.
- Won’t be able to relocate impressions correctly.
What must we do before taking a replica impression of a metal palate denture?
THICKEN UP the CHROME PART on the POLISHED SIDE of your denture with WAX prior to taking the primary impression. This will ensure the area of the palate is thicker and will accommodate the shellac and wax of the replica block.
How do we correct an OVEREXTENDED denture when taking a primary replica impression?
- Replicate the denture as normal yet PRESCRIBE ON THE LAB CARD for the SHELLAC TO BE SHORTER THAN NORMAL IN THAT AREA.
- There will be a longer wax rim in that area of the flange which can be easily modified care side before taking the secondary impression
Why do we take master impressions and THEN occlusion when making complete dentures (2)?
- Makes blocks more STABLE/ RETENTIVE.
- ANY DISCREPANCIES CAUSED BY THE IMPRESSIONS IN THE OCCLUSAL PLANE OR VERTICAL HEIGHT can be rectified.
Why do we take occlusion and THEN master impressions in partial dentures?
Enable us to
account for:
- Interocclusal space
- Tooth modification
prior to taking the master impressions
