Closed Tray vs. Open Tray Impression Technique?


Dr. L asks:
I have treatment planned a patient for a maxillary full arch fixed partial denture who has 8 implant fixtures. I generally used a closed-tray impression technique to pick up the transfer impression copings. But in this case I am concerned that the impression tray will lock on the transfer impression copings and I may have to cut off the tray. I am planning therefore to use an open tray impression technique for the first time. Any thoughts? Does anyone have any clinical tips on the open tray technique?

8 Comments on Closed Tray vs. Open Tray Impression Technique?

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Carlos Boudet, DDS
Dr. L You are correct in going to an open tray (or pick-up)impression technique versus the closed tray (or transfer) technique. One or two fixtures, the transfer should be fine, but when you talk about eight fixtures, I feel better with the open tray for the following reasons: 1- I have less chance of introducing inaccuracies by trying to fit the impression coping back in the impression 2- I feel better knowing that I won't lock the impression in the mouth in cases with divergent implants 3- I know there is less chance of distortion of the impression because the impression coping stays in it A good tip is to try the tray in the mouth and make sure you can feel the top of the impression posts with your finger, then when you take the impression, wipe your finger again to expose the top of the impression posts before the material sets. Once the impression sets, pick the material out of the hex holes and use a short hex drive to back out all the screws. Keep the screws organized if you have different sizes. Good luck!
Alejandro Berg
Agree with Dr Boudet. Another Tip that may help you.I usually use pattern resin (gc)to fixate the impresion copings(I have made little tube like pieces so wont have contraction tension),and after fixating them I unscrew all the copings and it should go out as one structure, if so i screw them back and take the impression if not, re fixate untill it does. If you have divergent implants only fixate the parallel ones. this gives you better certainty and precision
Gregori M. Kurtzman, DDS
I prefer to use open tray technique as I think there is less potential error and your more assured of accuracy. here is my technique 1. place the open tray heads 2. take a stock tray and make cut outs so that when inserted the pins protrude thru the tray 3. loosely link the heads with floss 4. in small segments place triad gel and light cure eventually joining them all together (remember polymerization shrinkage is a % of volume so small volumes have less total shrinkage verses curing a large mass) 5. mix a PVS putty and fill tray 6. squirt a medium body PVS around the gingival aspects of the impression heads and under the resin verification stent 7. insert the tray filled with putty so that the pins stick out, a finger easily wipes off the excess putty to expose the pins (material in cartridges even heavy body tends to run back over the pins) 8. after setting remove pins then remove impression
I would use open tray impression and and if this is a solid bar I would also splint all the transfer copings together. Pattern resin is great and the old way to splint the pieces together but takes a long time. Doing some "All or 5" or Nexsmile cases that use a cadcam bar I have used paperclips or heavier wire/tubing to splint all the copings together. Prebend (Shepard hook) on one end of the wire so it will hook over the back or hardest to get to Transfer coping. Use Triad and it is quick and easy to put the loop around a Transfer coping pull the wire tight to the next TC trim as needed then use triad get to glue both together. Keep repeating till you are happy with the splinting. Hook on the end makes it quick and easy to do not having to hold two ends up and try to stabilize them at the same time. Pull the hook tight place straight end against the next TC and triad and light cure.
Richard Hughes, DDS, FAAI
I have done this both ways with equal results, I take my inpressons with a PVS putty wash combo w/ spacer. My preference now for the maxilla, is with impresson abutments and impresson copings. I have not missed a trick yet. It is important for the Doc to hold the impresson steady with both hands.
Mark P. Miller, DDS, MAGD
All the above comments are great. I'll add my technique. I absolutely agree that an open tray technique is far superior when multiple implants are being impressioned. I first place the impression copings. Then I mix a putty, place it in the tray, pump it up and down on the impression posts and immediately remove it prior to setting. This way I know exactly where to drill the holes for the impression copings. I simply drill where the putty has told me to drill. It is quick and easy. For incredible accuracy I wrap floss in a figure 8 fashion and lute all the impression copings with Duralay. This is a very old technique dating back to the 70's and 80's. I don't use a putty, but medium viscosity tray material or heavy body depending on arch configuration, bridge undercuts, length of remaining teeth, pontics, embrasures, etc. Many older patients have pontics in contralateral quadrants, large embrasures, etc. You only have to lock a heavy body material in there once to understand why to use medium vicosity tray material. Then I inject light body material around the impressions posts and seat the tray. Always use regular set time impression material. You need the working time. Then about 30-45 seconds before the material set time is reached, I loosen all the impression coping screws until I hear the click/click that tells me nothing is screwed into the implants. When the timer goes off, I remove the tray just as if it were a closed tray technique. If you have a gagger, you'll be glad you loosened the screws ahead of time. As mentioned in other posts, wipe the impression material from the screw heads when seating the tray so you'll know where they are. If a screw retained prosthesis is planned, you can also wrap floss around the analogs/replicas, tie them together with Duralay or your material of choice, then pouring the stone. So you've tied the impression posts together AND the analogs. Extreme accuracy is important always, particularly in screw retained restorations. Good luck. Never stop thinking and innovating! !
Dr. Akhavizadegan
dear Dr.miller , use of putty as an indicator of impression coping is very good idea but loosening the screw befor material setting , decrease the chance of passive fitting of the restoration . in addition ; loosening the screws bofore complete material setting is only possible by the leave hands of tray holding and this increase the chance of impression rocking. be luck !
gpkaralis dds
I think most of the points have been made. Just one other thing that we do on big multi unit cases, is after we use the open tray impressions and have selected/fabricated the abutments on the soft tissue model. I'll then place the abutments, wax out the openings, retract and take an abutment level impression, which since at this point the divergences have been addressed, yields a very clean and accurate impression for the initial waxup of the casting. The abutments are returned to the lab with the soft tissue model and the lab will use the abutment/soft tissue model dies to complete the wax up and this process typically yeilds a perfect framework for the porcelain work. As such while I'm routinely using open tray impression posts, I am not splinting them anymore, because I'm not relying on that first impression alone. Anyway a little long winded and not to advocate a specific method, but to highlight the importance of a very close relationship with a seasoned lab and understanding their process, to give them what they need from the impressioning, to give you what you want for your patient.