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A good impression is the key to an accurately fitting crown and bridge
restoration. When the impressioning process is carried out correctly,
final seating of the restoration is carried out with minimal time and
adjustment. The following checklist outlines key points to be considered
for consistently successful simultaneous impressions:
- Use a rigid tray with the stability to prevent distortion.
- Ensure there is a smooth putty/wash junction without ledges. These
ledges are difficult to see in the impression but will become apparent
in the stone model. Occurrence of ledges can be lessened by preparing
a deep indentation in the putty (extending to the two adjacent teeth)
opposite the preparation site. Fill the indentation with syringeable
material and slowly, but firmly, seat and immobilize the tray.
- Ensure margins are captured in syringeable material and are free of
voids and tears.
- Make sure you have a very accurate impression of the adjacent and
contra lateral teeth, especially on the facial surface. Ceramists cannot
match surface texture and contours of the contra lateral teeth if they
can't see them.
- Ensure there is a good bond between putty and wash prior to removal
from the mouth. This bond is the last to reach sufficient strength.
Premature removal of the impression can lead to tearing of the syringeable
material from the putty. Tearing at the margins can be minimized by
better retraction of the sulcus and leaving the impression in the mouth
for the designated set time.
- Avoid tray burn-through. If the impression tray is not properly seated
and immobilized until sufficiently set, the preparation may contact
the tray. With weaker plastic trays, this can cause an expansion of
the tray that will rebound upon removal and create a tight-fitting crown.
- Record accurate detail in putty. The best impressions with putty are
obtained by seating the putty within one minute of mixing. If not seated
when fluid, the putty impression will capture less detail.
- Work in dry field. Rounded cervical areas or margins full of bubbles
are frequently caused by moisture in the sulcus. Be sure the prepared
tooth, sulcus and surrounding tissues are thoroughly dry prior to placing
the syringeable material. A dry sulcus is important. When using cords,
proper packing is necessary. If you can't see the margins, neither can
the impression material.
- Ensure there are no bubbles or pulls in the impression.
- Proper tissue management is critical for a good impression. Prepare
the initial finish line to the gingival margin. Then pack the retraction
cord and allow three to five minutes for the gingival tissue to retract.
Remove the cord and finish the preparation in an open and dry sulcus.
After prepping, place a large piece of retraction cord in the sulcus
and below the preparation line. Place a thicker cord on top of the first.
When ready to take the impression, remove the top cord, leaving the
bottom one in place and inject the impression material. Remove the remaining
cord after removing the set impression from the mouth.
- To avoid surface porosity in the model, avoid pouring polyvinyl siloxane
impressions for at least 15 minutes.
- Block out undercuts on prepared teeth to prevent the impression material
from tearing.
TOLL FREE Telephone: 1-800-661-9567
TOLL FREE Fax: 1-800-361-5088
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