Impressions for Implant Retained Prostheses
Impressions for dental implants can be looked at in two ways. Firstly impressions can be taken at either abutment level or at implant level. Secondly they can be with a closed tray or open tray technique.
Impressions for dental implants can be looked at in two ways. Firstly impressions can be taken at either abutment level or at implant level. Secondly they can be with a closed tray or open tray technique.
Let's take the example of a single implant.
An abutment in this context simply means the part that attaches a crown to an implant. In conventional terms, if the implant was a root, then the abutment would be the post and core. Thus an abutment level impression means that an impression is taken of an abutment in place on an implant. This is therefore very similar to conventional crown and bridgework. In fact sometimes the impression is exactly as you would take for a conventional jacket crown. However there are cunning little transfer devices that you can sometimes use which make this even easier.
An abutment in place on an implant. You could just take a conventional "abutment level" impression of this and then fit your crown in the normal way. However, there are transfer devices which can make this even easier.
Let's stay with our example of a single implant. In this case we have an implant sitting nicely integrated in the patient's bone but without an abutment attached to it. An implant level impression means that we are taking an impression of just the implant in place. In conventional terms this would be like taking an indirect impression for a post and core. However our conventional impression isn't going to work this time and we will always need a special transfer device. You will also hear implant level impressions referred to as "fixture head impressions".
A single implant in place in the bone. Our implant level impression will transfer the position of this implant to a working model.
The closed tray technique is pretty well the same as a conventional crown and bridge impression. In fact it can be exactly the same as a conventional crown and bridge impression as shown in the example below. In other circumstances a transfer device is used. Implant level or abutment level impressions can be taken this way.
In this example you can see an abutment being screwed into an implant. Following this a conventional crown and bridge impression is taken in a closed tray. This would therefore be a "closed tray, abutment level" impression.
Again this technique can be used for both abutment level and implant level impressions. In the open tray technique a transfer device pokes through a hole in the tray. After the impression is set you have access to the screw which holds the transfer device in place. This means that you can unscrew it and then lift it off with the impression. The main disadvantage is that you need plenty of space. Therefore where space is tight, like at the back of the mouth, you have to use a closed tray.
In this example you can see the transfer device (impression coping) being screwed directly into the implant. There is no abutment here. The impression tray has a window cut into it so that the transfer devices can poke through. After the impression is set you can expose the top of the transfer device and unscrew it from the implant. When you lift off the impression the transfer device is no longer attached to the implant so it stays in the impression. This example is therefore an "open tray, implant level" impression.
