Getting the best dental impressionHere is a great resource from 3M Espe
For the full printable download please click the file below
Here is a text only version.
Triple Tray Impressions
Many of our dentists use triple tray impressions routinely, we have a strict protocol
for handling them in the lab to ensure they do not distort and that the bites locate
However, we prefer to pour 2 models of every case; one to work on and one as a check
model - as can be seen from the image above, triple tray impressions often tear
making a second pour impossible.
Triple trays have to be poured in plaster with both arches together, this way a
lock can be made to locate the bite. However, if the patient bites through the tray
and makes a hole the plaster runs through. The hole can be seen on the image above
in the 5 region.
This image shows the resultant model, the yellow area on the 5 is where the opposing
die stone has run through. This means that anywhere where there is a hole the models
lock, this causes the model to break in this area and ultimately can lead to inaccuracies.
If you take this style of impression be please ensure that:
1. There is an adequate thickness of impression material to prevent distortion
2. The type of tray used has an imperveous membrane between the arches to prevent
the models locking
3. The impression material is stuck to the tray
The problem with quadrant impressions is achieving an accurate bite. even with a
good squash record the models have a tendency to rock. If, as a dental team, we
are looking for the highest quality we would like to recommend that we find an
alternative to quadrant impressions.
Another problem with quadrant impressions is there is half the arch missing...obviously!
This means we can only equilabrate the restoration in working side occlusion, we
are not able to do balancing side as the teeth which provide the guidance for this
are missing. Once again this can lead to a compromise in quality.
The impression in this photo is also so small that we have very little to go on
by way of reference. We can so few teeth that even a working side occlusal balance
will be difficult to achieve.
Lack of impression detail
Visual Appearance: Muted detail reproduction.
Result: Crowns may be too tight, or loose, and not fit correctly.
CAUSES & SOLUTIONS
For Polyether materials
with pH < 4 inhibit setting reaction, most commonly by contact with
acidic retraction materials and hemostatic agents containing
epinephrine or ferric sulfates.
Use retraction materials having pH ≥ 4.
Select retraction materials and hemostatic agents not containing these chemicals.
remove, and dilute hemostatic solution from the preparation with water
spray andsuction. Dry before taking the impression.
For all impressions
Impression material stored at elevated temperature.
Store impression material at room temperature.
Impression material stored at too low a temperature (prolongs the setting reactions,
changes viscosity and requires exceptionally
high extrusion forces for automix materials).
Keep impression material at a temperature of
18°C/64°F at least one day prior use.
Thick blood/saliva pooled around prep.
Remove blood and saliva prior to making impression.
Use 2-step impression technique.
Inadequate retraction of sulcus around prep.
Use good retraction technique, with proper moisture control.
Exceeding the working time.
Follow manufacturer's working time specifications.
Choose material with longer working time.
Inadequate disinfection effects surface quality (detail reproduction) and
Use water based disinfectants according to FDA guidelines.