In a prior post I discussed three tips to make triple tray impressions more effective.
But even when you do everything correctly you still will encounter problems from time to time. In this post I’ll discuss the two most common triple tray mishaps I see and how to overcome them.
(1) The patient bites into the tray
Don’t you hate it when this happens?
I wanted to take an impression for a single unit crown on # 5. I tried the tray in before the impression to make sure the patient could bite passively around the tray. But when I took the impression, the second molar clearly bit into the tray.
Some dentists will just look at the margins of # 5 and say, “Great! I got the impression!” Then at the insertion visit, they would find the crown didn’t fit correctly. Why?
If a patient bites into the tray, the tray will be distorted while the impression material sets. Once the patient opens the tray relaxes into its original, non-distorted position. This relaxation will be resisted by the impression material, but will still cause distortion depending on how heavy the bite was into the tray and the rigidity of your impression material. Either way, bad news.
I used to throw out the impression and try again. I don’t do that anymore because it’s wasteful and the patient may bite into the tray again anyway. Here’s what I do now.
Using an acrylic bur, I grind away the part of the tray that interfered with the teeth and mucosa. You’ll also want to lightly relieve the other teeth, especially the tooth that’s receiving the crown. Now retake the impression using your modified tray.
Much better. Notice that I still had a minor bit of the tray show through distal to the second molar. I wasn’t concerned about it causing any significant distortion.
(2) The patient can’t bite into a single position
Sometimes when I try in the tray before the impression, I’ll notice that the patient bites in protrusive. I’ll instruct the patient how to bite into maximum intercuspation and try again a few times for practice. What if they still can’t get it right? And what if they keep biting into some other weird position?
Whether your patient is simply confused about how to bite or he/she exhibits some odd muscle movements or tremors while closing, you’ll want to have a correct bite before you remove your cord and take the impression.
The solution is quite simple. Just place some bite registration material (Blu-Mousse, Jet-Bite, wax, whatever) on the contra-lateral side and guide the patient into the correct closed jaw position. It won’t interfere with the triple tray and it guarantees the patient will bite correctly during the impression.