We recently sent out a tech tip on Impressions - Best Practices, providing tips and instructions on how to take clear impressions.
This tip expands on the subject by providing a comprehensive list of the specific impression problems and procedural errors, their causes and how to avoid them. We will also show you the image of the impression itself compared to its digital model, for increased clarity of each issue.
- Description: The complete tooth anatomy and/or gumline was not fully captured by the impression material around it.
- Causes: This occurs due to insufficient material in the impression tray.
- How to avoid: Make sure you’re using enough material when taking impressions. Too much is better than too little.
- Description: This is just what it sounds like, it’s an air bubble in the impression
- Causes: 1. Bubbles occur while the impression material is being distributed, due to the mixing tip being lifted out of the material mid process, creating a hollow void under the material now placed on top. 2. Excessive saliva in the patient's mouth.
- How to avoid: 1. Keep the mixing tip inserted in the material while dispensing it. 2. Remove any excess saliva before taking impressions.
- Description: This is when the material itself captures the majority of the tooth anatomy, however the scanning process does not pick up the tray well, leaving that much of the tooth anatomy incomplete or distorted.
- Causes: Thin walls are created a number of ways: insufficient material, too small trays or the tray was pushed in too deep.
- How to avoid: 1. Make sure you’re using enough material – too much is better than too little. 2. Test the tray in the patient’s mouth. It should extend beyond the most distal tooth. 3. Don’t push the tray into the teeth too hard – you don’t want the teeth to push all the way through the impression material.
Double imprints (aka Shifts)
- Description: This is when you see two gumlines and/or what looks like two teeth imprints one right next to or on top of the other.
- Causes: 1. When the tray, full arch or quadrant is moved during the setting process. 2. If the first-step is not done correctly, for example, when taking the medium/heavy PVS impression and no plastic sheet is used over the first-step impression.
- How to avoid: 1. Make sure your patient is educated on the importance of not moving their teeth during the impression process. 2. Be sure to use a plastic sheet when taking medium/heavy body impressions on a two-step impression. The plastic sheet will create an impression of the large/rough shape of the teeth (like a custom impression tray).
- Description: A “pulled” effect around the gingival margin of the impression.
- Causes: 1. When the impression material prematurely sets before insertion and results in a “pulled” effect around the gingival margin. 2. When the impression material has not fully set and is removed (pulled) from the mouth too soon.
- How to avoid: 1. Once you've dispensed the material, put the trays in the patient’s mouth as soon as possible. 2. Leave the tray in the patient's mouth 60-90 seconds longer than the provided instructions.
- Description: When the impression material has torn in some way, breaking out of place and undermining the accuracy of the impression.
- Causes: 1. Tears occur when the patient has extreme undercuts or black triangles which causes the impression material to lock into the interproximal and tear when removing the impression. 2. Tears can also occur if the material has not fully set before removal.
- How to avoid: 1. Use wax to block out undercuts before taking the impression. 2. Leave the tray in 60-90 seconds longer than the provided instructions.
Improper 2-step impressions
- Description: When the second step did not bond to first step. In the above image, you can only see the green light-body material on top and you don't see the purple heavy-body mixed. This is how you know that the first and second steps didn't bond.
- Causes: By using incompatible heavy and light body material.
- How to avoid: Check heavy body and light body compatibility prior to purchasing.
- Description: Not enough material was used.
- Causes: Inadequate measurements of material for the size impression tray used.
- How to avoid: Too much material is better than too little material.
No light body
- Description: No light body was used. The light body and heavy body are usually two different colors, so that they can be identified easily. When the gumlines and occlusal anatomy is not well defined, there will be no sharp details and it will look rounded off.
- Causes: No light body was used.
- How to avoid: Be sure to use light body. See our videos on one-step and two-step impression techniques.
We hope this information helps you to take better impressions for the cases you submit to ClearCorrect. Check out our Help Center for more useful information on the topic of clear aligner treatment.
Until next time…