Introduction to impressions
Open tray impressions
Closed tray impressions
Express Abutment
Fitting implant retained prostheses
Managing the occlusion
Glossary of terms

Closed Tray Impression With Red Cap

This page shows how to take a closed tray implant level impression.  These are often called "fixture head impressions".  This example will show the impression for Neoss implants.  With one exception ( the very narrow 3.25mm implant) all the Neoss implants have the same width of restorative platform regardless of the  width of the implant itself. This is how it works:


As you can see, the top bit, the restorative platform, is always the same at 4.1mm.  This means that, unlike other systems, you don't have to use different sized components for different widths of implants.  They're all the same and this makes things very much easier.  You just order an impression coping and you know that it will be the right diameter.

In my opinion, the open tray technique is the most accurate and my first choice wherever this is possible.  However, the closed tray technique can be a useful alternative.

YOU WILL NEED:

A Transfer Device
You will need an impression coping for each implant,  They come in different lengths, 8mm, 11mm and 18mm but they are all the same width.  The 11mm impression coping will be good for pretty well all your impressions.  You would only need the 8mm or 18mm if the adjacent teeth are exceptionally short or long.  The newer Neoss impression copings have a retentive block around the shaft and look like this one on the left.


These are no good for the closed tray technique.  You need to order the ones that say 'impression coping' but not 'impression coping open tray'.  The ones you need for this look like the one on the right.
An implant replica
You will need an implant replica for each implant but they come in the pack with the impression coping.
The screwdriver from the prosthetics kit
One big advantage of the Neoss system is that there is only one screwdriver. There are different lengths though.
A special tray
Ask for acrylic, 3mm spacing, perforations and a stepped handle.  It is also possible to use a disposable plastic impression tray as shown below.  This is often fine for a single implant but not recommended for multiples.
Impression material
We recommend that you use impregum mixed in a pentamix machine.  Nevertheless, the material is is less critical for single units and other crown and bridge materials can be used successfully.


When you receive the impression coping from Neoss, it will look like this.
It comes with an implant replica and red cap already in the packet.


PROCEDURE:

You are unlikely to need local anaesthesia for these procedures.  However if the healing abutment is not fully seated or has come loose there may be some soft tissue over the head of the implant.  In this case you can use a gingival infiltration of local and remove the excess tissue with a scalpel or, very often, you can just push it out of the way with the impression coping..

Also check for obvious undercuts such as bridge pontics.  If you use impregum it is very rigid and you may need to block out undercuts with some wax first.  If you use a special tray, another good tip is to prescribe your tray, for upper teeth, as a horseshoe shape.  If you have a full palate, the impression material can form a really good peripheral seal making it difficult to remove the impression.

Remove the healing abutment
Firstly you need to remove the healing abutment which is in place on the implant.  Use the screwdriver from the prosthetics kit.  The healing abutment should just be finger tight.  Keep the healing abutment safely.  You will need it again.  I like to soak it in 0.02% chlorhexidine mouth rinse until I need it again.  Don't remove the healing abutment too early because the gingivae will start to recoil over the implant head and it will be sore for the patient to place the impression coping.  If there is more than one implant then remove the healing abutment and place the impression coping one implant at a time.  Also keep the healing abutments in order so that they can go back onto the same implants.  They may be of different heights.


Neoss healing abutment in place

Fit the transfer device
Pick up your impression coping and pull off the plastic tube.  You don't need that for the closed tray technique. If it's hard to get off just grasp it with a pair of ortho pliers or just bend it over and get you finger nail behind it.  It will come off.  Take a look at the top of a Neoss implant.  You will see that it has six locating "slots".


The impression coping has to locate into the slots in the head of the implant.  Take your impression coping and place it into the implant with the screw end first.  Screw the impression coping lightly into the head of the implant with your fingers.  A big advantage of the Neoss system is that you cannot screw the impression coping into the implant head unless it is properly located.  The thread is deliberately too short to allow you to do that.  In other words, if you are screwed into the implant head then you are properly located.


Take the screwdriver again and secure the impression coping fully onto the implant by screwing it finger tight.  At this stage some people recommend that you take radiographs to check that the impression copings are fully seated.  This is not necessary with the Neoss system because of the short thread.  However if it is the first time you have done it and you are not sure, you may prefer to take a radiograph.  You will be checking that there is no gap between the head of the implant and the impression coping. (There won't be).

Fit the red cap


The red cap just pushes onto the impression coping, BUT, it only fits in one orientation so you have to spin it in your fingers until you feel it fully push down.  The best thing to do is to practice first with the impression coping out of the mouth.  You'll then feel how the red cap fits onto the coping and you'll recognise that when you do it in the mouth.  The other thing is, you don't want it to touch the adjacent teeth. This could displace the red cap and, of course, that will lead to distortion of the impression.  In the case above you can see that the distal of the canine is quite bulbous.  To avoid contact, you can trim off the corners of the red cap like I did here. It's only plastic and cuts really easy, say, with a diamond bur.  Before you take the impression, take your dental mirror and look straight down the long axis of the red cap to make sure that there is no contact with the adjacent teeth.

Take the impression
Try the tray in the mouth and you're ready to go.  I've used impregum here. It's quite rigid and so it engages well around the red cap.  When the impression is removed from the mouth the red cap is engaged with the material and so it's lifted off the impression coping when you take the remove the impression.


Your next job is to take the Neoss screwdriver and remove the impression coping from the implant.  Put your healing abutment straight back in before you do anything else because the gingivae recoil really quickly over the implant.  If you leave it for any length of time it can be quite sore for the patient when you put back the healing abutment.

Now take the impression coping and the implant replica which came in the packet.  Use the Neoss screwdriver to screw the two together as demonstrated below.


Now the whole assembly of impression coping and implant replica goes back into the red cap in the impression. It's just like before, it only goes in one way so you have to twist it in your fingers until you feel it can push fully into the red cap.  In fact, it you look inside the red cap you'll see why this is.  It has a flat on one side which matches a flat on the impression coping.


Crown and bridge stuff
That's it. You now need all the other bits of conventional crown and bridge like an opposing impression, shade etc.



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