Implant Specialist and CDT Alex Rugh discusses the difference between open and closed tray impression copings and cautions about the adverse results of using them incorrectly.
Today I want to talk about a common mistake we see with implant impressions, and that is impression copings being used incorrectly.
Implant impressions can be taken using either the closed tray or open tray technique and a specific type of impression coping is required for each. One of the things we see often is open tray impressions that have been taken with closed tray impression copings and vice versa.
Unfortunately, this misuse of the impression copings can lead to inaccurate models.
Closed tray impression copings are designed to be easily removed from the impression after it has set up. They have shallow retention features with soft edges that allow the impression coping to softly snap in and out of the impression without tearing the impression material.
They are also designed with indexes or flat sides so that it’s easy to re-insert them back in the correct rotation. Some impression copings are designed so that they can only be re-inserted in one specific orientation, and other can be re-inserted in several different rotations that are all accurate.
One thing that almost all closed tray copings have in common though is that they rely on the bottom of the tray as a vertical stop. If a hole is created in the tray, that vertical stop is removed, and we lose vertical accuracy.
Open tray impression copings are designed so that they are NOT easily removed from the impression. They have hard edges and deep features that provide retention and allow the impression material to lock them in to place.
If an open tray impression coping is used with a closed tray technique, the coping will rip through the impression material when the impression is pulled. This will reduce the accuracy of the impression if the lab tries to reinsert the impression coping to pour up the model.
Additionally, many open tray copings are designed in a way that makes it possible to re-insert the impression coping in the wrong orientation. An example is this Astra EV impression coping that has identical anti-rotation slots all around it and yet there is only one correct rotational orientation. Once this is removed from the impression, it is impossible to determine which way it should be re-inserted.