17 Tips for taking a Good Impression
Thirty percent of conventional impressions recieved by laboratories are inadequate, according to respondents to LMT’s State of the Industry 2010 Survey.
Here, Manufacturers offer impression-taking tips.
Seat impression tray with a slow, steady, vertical seating motion to allow for blending of tray/wash materials.
To reduce voids, use a stirring motion while syringing and keep the syringe tip immersed to avoid trapping air.
To avoid tearing at the margin and insufficient retraction, displace tissue to allow the impression material to better access the prepared are. Also use an impression material that ensures sufficient tear resistance, such as Impregum.
To ensure dimensional stability, the impression must be placed in a Ziploc bag no more than 120 hours after washing, rinsing and removing excess water.
If it is necessary to delay the pouring of the model, wrap a wet towel around the impression and store it in a plastic or sealed container.
Always keep the material in front of and ahead of the syringe tip, and only push the material forward. Don’t lift or pick up the lip while pushing the material around the margin.
Make sure the tray is adequate enough to allow 2mm of impression material between the tray walls and the teeth.
Use passive pressure to hold the tray in position until completely set.
Don’t allow the material to slump or drip into the oral cavity.
Wash material should be syringed 360* around the preparation.
To avoid pulls and voids, submerge the intra-oral tip into the material until you finish syringing around the preparation.
Use the correct type of double-bite impression trays to prevent distortion.
Use a dual-phase technique for better accuracy.
Use a double cord retraction technique to obtain better impression.
If your impression material fails to set around the prep, check to see if the retraction cord contains sulphates which inhibit the set of PVS materials.
If you are using wash and tray materials from different manufacturers for single step impressions, check the set times of both and leave the impression in the mouth as long as is needed for the slower-setting materials to fully set.
When taking a second-wash impression inside a previously taken impression, relieve the contact areas of the first impression prior to taking the wash impression. This minimizes the possibility of tight contacts in your final restoration.