Impression Material

Alginate:

The alginate that is used should retain its shape under any conditions and must not contain any air bubbles. Any type of alginate can be used but for the best results, OrthoProof recommends alginates with at least 100 hours dimensional stability.

It is very important that there is NO BITE THROUGH of the impression material. Tooth contact with the tray can lead to errors in the digitization process.

Impression technique:

For consistency of outcome, OrthoProof recommends the use of an auto mixing machine, however, with the optimal technique, hand mixed alginates can be just as good. Ensure that the patient has rinsed their mouth and has spit out or swallowed just before taking the impression.

Mixing:

Using the auto mixer, mix one unit of alginate. If hand mixing, dispense the correct proportions of powder and water into a clean mixing bowl according to the manufacturer's instructions. The water should be tepid, near to body temperature. Mix the alginate according to instructions, making sure that it is well mixed and that there are NO air bubbles trapped in the mix. Frequent squeezing out of the air in the mix by flattening the spatula and squeezing the material against the side of the bowl will ensure a smooth homogeneous mix.

Loading:

Load the alginate into the tray, pressing down on the material with the spatula to ensure that the alginate flows into the retention holes. Run very cold water from the cold tap in the office sink and with the flow rate of the tap water set fairly low, place the tray containing the alginate under the stream of water. Using a finger, smooth the surface of the alginate with the very cold water. This should provide a smooth skin on the tray contents.

The additional benefit of this technique is that the very cold water retards the set of the surface layer of the alginate, allowing the deeper tray contents to start setting a little ahead of the skin. This produces a heavy body / light body effect within the alginate, making the impression smoother and more accurate.

Taking the impression:

Pick up some excess alginate material from the bowl and smear it with a finger tip over the incisal and occlusal surfaces of the teeth to be impressed. This will greatly eliminate the chance of an air bubble in the impression. If there is enough time and material, it can be manually smeared into the buccal reflections.

Orientate the tray into position and gently press home, starting with the posterior end of the tray, to ensure that the excess material is forced to the front, not down the patients throat. This is much more pleasant for the patient and less work for the staff not having to clean up the consequences of not doing this!

When the alginate has set, gently pull the lips away from the edges of the tray to break the airtight seal that has developed. Using a gentle rocking motion to start with, ease the tray out of the mouth in a straight path from the arch. This should ensure that the material does not tear and also that it is not pulled away from the tray.

Post Impression:

Inspect the impression for quality and if it is of a high standard, rinse and disinfect according to practice protocols. The alginate should be shaken free of excess water and then either:

• Wrapped in some wet paper towels (not too wet as the alginate continues to absorb moisture and can become distorted)
• Squirt approximately 2 mm of water into the incisal and cusp tips

Seal the alginates securely into a zip-lock bag and put into the fridge until they are ready for dispatch.

Suggested Resources:

Kromopan 100
Alginmax 120

PVS:

Any make of PVS may also be used as the impression material. All of the above criteria for Alginate also apply to the use of PVS material.