Problem

[PGguy]

Something weird is happening to me for the first time. Some how my crown is shifting in the investment. All I know is the crown is "****-eyed". I am doing a e-max over and implant abutment. My margin has shifted and is filled with pressed porcelain. When I devest there is a thin layer of pressed porcelain over the opening of the crown(flush with the margin.)

Does this make sense? what is happening? I am doing nothing different when I invest. Is my angle wrong when I sprue?

pgguy

 

[sixonice]

Something weird is happening to me for the first time. Some how my crown is shifting in the investment. All I know is the crown is "****-eyed". I am doing a e-max over and implant abutment. My margin has shifted and is filled with pressed porcelain. When I devest there is a thin layer of pressed porcelain over the opening of the crown(flush with the margin.)

Does this make sense? what is happening? I am doing nothing different when I invest. Is my angle wrong when I sprue?

pgguy

The abutment is shifting in the investment. Just like with any press-to-metal system they tell you to wax small "T" bars or fishhooks to the substructure that is getting PRESSED TO. Understand, your pressing under fairly high pressure and even .5mm of movement can cause the flash your describing. This little mechancial retentive device prevents any movement whatsoever in the investment. What kind of abutment are you pressing to? Metal or zirconia? Zirconia abutments can be stabilized with an old cosmopost (which is also zirconia) placed inside the abutment during investing.

 

[PGguy]

I should clarify that it is not the actual metal abutment, the doc left the abutment in the mouth and took an impression of it hahaha. It's a regular model, just that the prep is shaped like the metal abutment.

Yes "Flash" was the word I was looking for, it partially covers the margin of the crown, across the "opening"

 

[Al.]

I should clarify that it is not the actual metal abutment, the doc left the abutment in the mouth and took an impression of it hahaha. It's a regular model, just that the prep is shaped like the metal abutment.

Yes "Flash" was the word I was looking for, it partially covers the margin of the crown, across the "opening"

That just happens every once and a while. I would guess I get that exact thing once in every 200 units.

I have no idea why, I redo it the same way and it goes.

One time I had a little 3 unit ant bridge and one of the abutments was a very long and narrow prep but the crowns and pontic were heavy. 4 times I had miss presses. The investment would break down and it would come out solid.

I ended up doing it in pfm. There was something about the design and shape of the prep in combo with the force of pressing like Six Pack of Corona said that caused the investment to crush.

 

[PGguy]

What I learnt about E-max,

For fabrication of long thin abutments(an implant abutment in my case) Sprue the crown straight up, no tilt. margin at the highest point. For some reason I was getting investment blown out when I had it tilted. Too thin with all the pressure, I guess.

5th times the charm.