There is a range of dental procedures in which impression materials are used to take an impression of teeth and surrounding tissues. Preliminary impressions are taken mostly by the dental assistant and are used to create a reproduction of the teeth and surrounding tissues. A preliminary impression is used for the following procedures: Diagnostic models/casts, custom trays, orthodontic appliances, and pretreatment/posttreatment records. Today, you will be learning how to take upper and lower preliminary impressions because this is something that will be done daily in the dental office.
Step 1: Supplies
So to get started you will need to get all the supplies ready. You will need alginate powder, room temperature water and water vile, alginate scoop, a flexible bowl, wide spatula, a smaller bowl, and trays.
Step 2: Measuring
The next step will be to measure out the alginate powder and the water. The first thing you always do with the powder is to fluff it, shaking it up and down. You then can measure out one scoop of powder and set it to the side. After the powder is measured, you can measure your water. You will take room temperature water and fill the water vile to the top. You then can also fill the smaller bowl with a little bit of water, this one does not need to be measured. Pour the measured water into the flexible bowl and get your scoop of powder ready.
Step 3: Mixing
Once the powder is in the water, you can begin the mixing period. You will mix vigorously against the side of the bowl in a left to right matter for 30- 45 seconds. When it comes to impressions, you always want to do the lower first. Once the mixture is a creamy pink color, you may get ready to load the tray.
Step 4: Loading the Lower Tray
Loading the lower tray, you will want to load from one side and work your way around. Once you have most of the mixture in the tray, you will take a tootsie roll size of the mix and put it in the patient's frenum area to create that vestibular roll. While the mix is in the tray, you will then dampen your finger and press material toward out edges. After you dampen the material, you are ready to place the tray in the patient mouth.
Step 5: Inserting Lower Tray
You will place the tray sideways and rotate it into position. You want to make sure the tray is centered in the patient's mouth. Line up the handle of the tray with the patient’s central teeth. You will then lift the patient's lips as the tray is placed. To place the tray correctly, you will press down the posterior to form a seal and the anterior. Then ask the patient to lift and protrude the tongue. Impressions can be difficult for some patients, so while you’re waiting for the impression material to harden, talk to them and distract them.
Step 6: Loading Upper Tray
Loading the upper tray, you will want to load all at once and place more in the anterior. You then again would dampen your finger and press the material out towards the edge.
Step 7: Inserting Upper Tray
The placement of the tray in the patient’s mouth is also the same. The reason you will do the lower impression first is that it is the easier one of the two. Patients on the upper impression tend to gag more. So, with the upper impression, you will lightly hold the patient's head between your arms and lean their head forward. Again, you want to talk and distract them, so they don’t think about gagging.