Diagnosing an Impression Problem

[Brett Hansen CDT]

I have a periodontist that sends me cases with stock abutments to modify and send back to him. Sometimes we do the full crowns for him. A few times, we have had to redo the crowns because the implant analog was not orientated in the same manner as the implant. This doctor uses Southern implants(nobel tri-lobe knock off).

He sent back a case today for an anterior tooth(#7). He sent in a new impression and the old. I removed the analog and imp coping from the new impression to make sure it was situated correctly and then placed it back into the impression. I also put together an analog and imp coping to make a new model out of the old impression. As you can see from the attached photos, they are not the same.

My question is, what do you think went wrong? What do I tell him? He isn't blaming us, but he would like to know what to fix on his end if I can diagnose the problem. I won't know until tomorrow if the analogs for both impressions are at different relative heights to the crest of the tissue which might indicate that the imp coping was seated fully on the first impression.

 

[rkm rdt]

I've had those problems when the Dr uses light body material.It's hard to tell what you have there .

I find that some close tray brands have lousy orientation groove designs . Combine that with the light body and it's a crap shoot.

 

[Brett Hansen CDT]

He uses Impragum(sp?). It is very rigid once it sets up. No light body was used. The impression copings don't have the greatest retentative design...they are 2/3 round with 2 flat sides that make an edge for the other 1/3.

 

[Mark Jackson]

My question is, what do you think went wrong? What do I tell him? He isn't blaming us, but he would like to know what to fix on his end if I can diagnose the problem.

The problem is, he didn't have the impression post engaged into the fixture properly. He needs to take a PA of the impression post before he takes the impression to see that it is seated down into the fixture.

 

[Bobby Orr ceramics]

For single unit analogs have the doctor inject a very rigid bite reg material called O-Bite from Zenith(DMG) around each impression analog in the mouth......only around the base. The material is 94% rigid. Let it set completely. Then the dr proceeds to take impression. This will anchor the analog within the impression during pour up.

For bridge case..... The dr injects the O-Bite around each analog and connects them . Let it set completely. Loosen the the analog screws, and test the draw of the analogs as one unit.....it becomes an instant verification jig in the mouth. Tighten up the screws and proceed with impression. If the verification jig is good in the mouth, it should be predictable on the model when poured.

PM me if you have any questions. Orr(James)

 

[Jo Chen]

"The problem is, he didn't have the impression post engaged into the fixture properly. He needs to take a PA of the impression post before he takes the impression to see that it is seated down into the fixture."

The x-ray should be taken perpendicular to the long axis of the implant to get a clear view of the implantabutment interface.
The first picture shows a good example. The second picture although not a impressioncoping but a abutment illustrates incomplete seating. I always request a copy of the x-ray along with the impression. Tell the Dr. it is like buying insurance including the x-ray.

 

[Brett Hansen CDT]

Now, the rest of the story....

So I analyzed the models I poured up from the new impression and the old impression. Both analogs were at the same depth in relation to the gingival height, so that told me that, most likely, he did get the impression coping seated in the implant both times. I began inspecting the realtionship between the retentive sides on the impression coping and the lobes on the implant analog. To my dissapointment, I figured out that I didn't get the impression coping put into the new impression correctly. This was after spending alot of time going over both impressions and then carefull inserting the imp coping/analog into the impressions.

After a few minutes of self-flagellation, I called up the oral surgeon to tell him what had happened and why I thought it happened. These are 3.5mm platform implants. This means the rentenative surfaces of the imp coping are small. In addition, when I put the imp coping into the impression, they don't fit tightly...there is a few degrees of rotation. I can never be 100% sure that the imp coping is lined up exactly where it is supposed to be. The oral surgeon was in complete agreement with my observations and they coincided with his. He had actually called up the Southern president and talked to him about redesigning the impression coping for the 3.5mm because another of his big reffering doctors has had the same problems.

Solution to this problem in the short-term is that he is going to start using a lightbody around the impression coping to help tighten up the retention. I think this will work. It would be better if the impression coping for Southern had the same type of retentive design as Nobel's 3.5mm, but then it wouldn't be as inexpensive(I guess).

Thanks for all the responses!

 

[Jo Chen]

Thank you for the update and helping us to avoid this issue. It takes a real man to admit a mistake.
It hurts to make a mistake, makes you feel like a dunce. Don't despair we all have our slip ups.

In the meantime while Southern Implant is redesigning the impression coping have the restoring dentist mark the buccal/labial of the impression coping with a sharpie or even better create a undercut/indentation with a round drill on ther buccal/labial