When it comes to implant impressions do you prefer open or closed tray impressions? For me, the biggest reason I prefer closed tray is I hate trying to get the impression transfer through the hole in an open tray and then gain access to the transfer so it can be unscrewed and removed with the impression from the mouth.

The other reason is that if I need to retake the impression I have to dig them out first and replace them in the patient's mouth.

 

Despite my preference for closed tray implant impressions they are not appropriate for all cases. Dealing with full arch implant cases or cases with divergent implants are two prime examples of when open tray impressions are a must.

The cases described above are also the hardest cases in which to get all the implant transfers smoothly though all the holes in the tray (at least for me). It helps to design a custom tray with "guide cones" to guide the impression transfers though the holes in the tray.

The first step in fabricating this type of tray is to take a preliminary impression so that you can have a model to fabricate the tray on. The next step is to take stone or resin and build your "guide cones" over the healing abutments on the model. While it adds to the fabrication cost, my preference is to use resin for the guide cones because it's easier to work with. My favorite material to use for this is Triad Trans Sheet. This material is simply a thin sheet of light cure resin that you can mold easily with your fingers to shape your cones.

As you can see in the photo, the guide cones in this case vary in size. This is due to the fact that the positions of #2 and #15 are for single implants and the others are for groups of two and three implants. The big thing to remember when making these guide cones for groups of multiple implants is to keep the groups as low in number as possible, and make certain the most mesial and most distal implants are your guides for the group.

It's worth noting that these "guide cones" could be made with wax, but almost any method of forming the tray material is going to involve significant heat at some point. If you do use wax, expect it to melt and make a big mess. There's also a good chance that you'll end up with distorted cones and have to start over.

In part II, I'll discuss how to form your tray and take an impression.

John R. Carson, DDS, PC, Spear Visiting Faculty. [ www.johnrcarsondds.com ]

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Comments

Commenter's Profile Image Gerald Benjamin
March 1st, 2014
John, The easiest way to take an open tray impression is using the Miratray Implant tray by Hagen. This cellophane backed tray permits the long screws to poke through making them easy to locate and retrieve.
Commenter's Profile Image John Carson
March 1st, 2014
That's an interesting looking tray Gerald, thanks for the info. It looks like it would be very easy to use especially for cases with a limited number of implants and a significant number of remaining teeth. Have you used it on fully edentulous cases, if so how was it? Thanks again, John
Commenter's Profile Image Gerald Benjamin
March 1st, 2014
I have not used it on fully edentulous cases but I am about to. I will let you know. I have had no remakes with this tray.
Commenter's Profile Image John Carson
March 2nd, 2014
Thanks again Gerald, I would love to hear how it goes! Having only seen pictures of this tray one thing that I would be concerned about with this tray and a fully edentulous case would be getting a good impression of the tissue while still maintaining enough material around the implant transfers. When I make custom trays for these types of impressions the tray ends up contoured so the top of the transfer just pokes out the top of the tray this assures plenty of impression material around the transfer to hold it firmly in place. While the tray you mentioned here may very well do this too, it's just something I would be sure you check as it seems like it might be easy to over-seat the tray and end up with unstable transfers due to too much of the transfer sticking out of the tray. Part II will detail what I am talking about more.
Commenter's Profile Image Gerald Benjamin
March 2nd, 2014
Hi John; You are very wise. The key is to just have all of the abutments about to poke through the cellophane so that you can easily locate them at the appropriate time. There really is not a lot of loose soft tissue around implants especially if extensive grafting was done to build bone. I have done a full maxillary reconstruction with 6 implants and 5 veneers using this tray and had no issues. Time will tell. I look forward to your next article.