One of our new assistants has been struggling to get exquisite alginate impressions. Together we came up with an approach to getting the kind of impressions we need for our patients and accomplish some training, we would do them together for a while. The alginate we use int he office has three different color phases to assist you in the timing of mixing, seating the tray then knowing exactly when the material is set. On the first impressions we did together I noticed how quickly the material was setting. So quickly it was making it impossible to mix adequately and get the tray loaded and seated.
I asked if we could have bottled water from the refrigerator for the the next impression and got a quizzical look. The set time of alginate can be modified by multiple factors, including the water temperature and the powder to water ratio. One of the things I am pretty picky about is not playing with the water to powder ratio when mixing alginate. Yes we can alter the set time, but we also alter the properties of the material, potentially altering the accuracy as well. Accurate impressions depend on managing the material, including knowing when it has reached an appropriate set so we can remove it from the mouth.
The set time of alginate is inversely proportional to the temperature of the water, so the colder the water the longer it takes to set, and you gain lots of working time. If you are looking to speed up the set, make the water warmer. All alginate comes with a recommended water temp at which the working and setting times are designed. What we needed was more working time, although adding lots of extra time in the mouth isn’t always to our advantage, so cold water was the key. The next time we mixed we split the water and did one measure of tap water and one measure of bottled from the fridge. It worked like a charm, we had lots more working time to mix and load the tray. The beauty of this technique is once int he patient’s mouth their body temperature warms the material again and returns the set times to near normal. With our alginate I know that once it has turned from pink to white we have ninety seconds before it is ready, and it simply took about 20-30 seconds longer to go from pink to white int he mouth.
Just like measuring water and powder precisely, manage the temperature of the water you are using so the material behaves as expected. If you need to alter the working or setting times, plan to intentionally alter water temperature.