Dental Technology



Taking an alginate impression is one of the most common procedures done in a dental office today, but did you know that it can quickly become one of the most costly? Minor discrepancies in technique can significantly impact the accuracy of the final product, leading to remakes, extra chair time and possibly even the need for a new impression. Remembering these simple tips will help you take a better alginate impression the first time, every time.

What makes it good? This well-done impression of a lower partial ensures a very accurate fit because all land areas are captured and there are no distortions.
Mix it up right

  • Check the water-to-powder ratio: Typically we see too much powder in the mix, which causes the consistency to be grainy. This usually occurs because the alginate was not shaken up in the can before it was measured out. If there is too much water in the mix, the material will be too thin, causing the impression to tear upon removal.
  • Verify water temperature: If the water is too warm, it will decrease mixing time and prevent a smooth mix. If the water is too cold, the material will set too quickly. The ideal water temperature is 70°F.
  • Mixing order is important: Always add powder to water, not water to powder. This ensures that all of the powder is fully incorporated. Once incorporated, mix vigorously for one minute to achieve a creamy consistency, which helps the chemical reaction occur uniformly.

It's all in the details

  • Prep the patient properly: Have the patient thoroughly rinse his or her mouth to remove debris, cut mucin and lower surface tension before taking the impression. Lightly dry the teeth with compressed air.
  • Select the right tray: The tray should cover the areas needed for the impression and still allow for adequate clearance between the tray and the tissues. When finding the right tray, there are times when you may need to extend the posterior area of the tray with red rope wax so you capture the retromolar pad on the lower and the maxillary tuberosity. This is especially important when taking impressions for dentures.

Better removal in a snap

  • Patience is the key: If the alginate is still in a plastic state upon removal, impression detail will be lost. So be certain to keep the impression in the mouth for a full two minutes. Leave a test sample in your mixing bowl. When your sample starts to set, start timing your impression.
  • Working the tray: When removing the impression from the maxillary, you can use each of your index fingers and place them all the way back posterior on the masseter muscle to release the suction and pull down.
  • Remove rapidly: Alginates are less likely to tear when you remove the impression quickly. Avoid rocking or twisting when removing the impression. Instead, remove quickly with a snap.

Don't forget to inspect your alginate impression. This is an essential step in saving time, money and heartache - for you, the lab and the patient.

So remember:

  • Check your impressions carefully before they are poured up in stone.
  • If you're unsure about the accuracy of your impression, take another one while the patient is still in the chair.
  • Always review your models for accuracy before you send them to the lab.

At DDS Lab, we make each dental prosthetic to fit precisely to the model you send; if the impression details aren't accurate, then the mould is wrong. Ultimately, that means the dental prosthetic we deliver to you will not fit correctly in the patient's mouth. Taking a good impression and minding the details helps us all deliver a better dental prosthetic to the patient.

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