Custom abutment help

wwcanoer

wwcanoer

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Help! What am I doing wrong?

This is my first case for screw retained PFM's. #8, and #9 with cantilevered #10.

The first one, # 8, I just had flash on the outside of the platform, and was able to rubber wheel it off.

The second casting was for the cantilevered bridge,#9 and #10.

As you can see from the pictures, there is flash on the outside going around to the inside of the platform!

The metal is Aquarius Hard cast to an Implant Direct custom abutment. Investment was Creare--vest high heat investment. I used half millimeter less liquid, half millimeter more water than for a regular casting when investing for Aquarius Hard metal as advised. I have found that I have to use a thick bead of wax at the junction of the wax and the abutment, or I end up with voids, and two vent wires. I don't have problems with screw retained gold crowns, or with cast gold custom abutments.

Still too much expansion?

These two were cast separately, but with identical techniques. Any thoughts and advice would be greatly appreciated.

Carol
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aidihra

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Maybe I need glasses, but is that investment where the screw hole should be?
 
JohnWilson

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Measure you liquid for less expansion, burn plastic parts out longer and slower to avoid investment breakdown as the pattern expands. Heat soak longer than normal. If you have to rubber wheel flash off the interface there is a definite problem with your liquid ratio.
 
wwcanoer

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Yes it's investment, didn't bother cleaning it out after discovering all the flash making it a worthless piece of metal :(
 
C

charles007

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I haven't cast these before ! Remember that plastic is very easy to get flash, just like plastic attachments or older solid plastic sprues.......
Use a 2 stage burnout with a slow rate of climb. Be careful using debubblizer, blow off well.
 
Al.

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I haven't cast these before ! Remember that plastic is very easy to get flash, just like plastic attachments or older solid plastic sprues.......
Use a 2 stage burnout with a slow rate of climb. Be careful using debubblizer, blow off well.

Thats exactly what I was thinking. 10 F degree per minute climb to 600 F, hold for min of 30 minutes then 10 F climb to max temp.
 
wwcanoer

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These are "gold engaging abutments" with a plastic sleeve. Goes in a cold oven to 6oo F at 10/min for half hour, then to 1450 F at 10/min for half hour. As I said before, this is the same for burnout schedule I've used forever with Aquarias Hard.

I've talked to the other two labs in town. One suggested an extra wind on casting- doesn't sound right to me, other lab had similar problems with the Nobel Biocare abutments, but they have switched to an electric casting machine.

I'm leaning towards decreasing the expansion, and the longer burn out time-heat soak.
 
JohnWilson

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These are "gold engaging abutments" with a plastic sleeve. Goes in a cold oven to 6oo F at 10/min for half hour, then to 1450 F at 10/min for half hour. As I said before, this is the same for burnout schedule I've used forever with Aquarias Hard.

I've talked to the other two labs in town. One suggested an extra wind on casting- doesn't sound right to me, other lab had similar problems with the Nobel Biocare abutments, but they have switched to an electric casting machine.

I'm leaning towards decreasing the expansion, and the longer burn out time-heat soak.

Good idea, also you do not want more force with casting machine.
 
C

charles007

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Extra force in the arm can create turbulence , rough casting etc
 
Al.

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Finns are from the investment cracking, so I assume buy decreasing the expansion you are using more special liquid and have a denser and stronger investment?

Just curious what investment are you using?
 
wwcanoer

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Leach & Dillon Creare-Vest, been using it for years.. ever since Whipmix had their problems with their high heat stuff 10-15 years ago. Having a senior moment, don't recall what it was called:D

carol
 
kcdt

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Finns are from the investment cracking, so I assume buy decreasing the expansion you are using more special liquid and have a denser and stronger investment?

Just curious what investment are you using?
Don't you mean the other way 'round. More special liquid = more expansion?
 
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alamarlab

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You have "over expanded" the investment. Which is fine if you like your copings a little "loose", but it allows the alloy to slip past and over the abutment (which doesn't expand as much as the investment). Adjust your investment for less expansion/tighter fit, usually more water/less liquid, same total volume.

I use a ringless system, Talladium Galaxy Universal Investment with their suggested dilutions, 20 min bench set, 20 min hot rapid burnout 1550F/843C.

Only miscast I ever had with abutments was when the Implant company sent me a Titanium abutment instead of a gold "cast to" one. FYI, the Titanium melts and becomes part of the ruined casting. Not a pretty picture.

Your investment may not be strong enough to handle the expansion of the plastic abutment part, which sometimes expand before melting.

Galaxy is a very strong investment, never had fins or blown up in oven with the rapid burnout technique. I have even pushed it with a 10 min set, 10 min burnout. Pretty cool to have a casting in 20 minutes. Of course I am sure all of you have never been rushed. Must be just me....j/k (Been doing this for 40 years now)

Good luck, Steve
 
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CatamountRob

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I did one of these a week ago (Nobel Biocare Goldadapt),all I did was sprue it with a 10 ga. direct sprue, put a single vent on the back side and invested it with WhipMix PowerCast. I cast it in d.sign 91 (60 percent AU) and it cast perfectly. I used a slow burnout, 15/min to 600 for 30 min. then 20/min to 1400 40 min. hold. Rob
 
wwcanoer

wwcanoer

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Possibly the rest of the story.

A week, and a couple castings later, after I did that failed custom abutment, I thought the spring on my machine had broken. You know the feeling, you go to wind it up, and nothing happens. Take everything apart, spring (probably 24 years old) looks okay, but switch it out for a new one just to be on the safe side. Reassemble everything, but it still won't wind. Call the tech help people at Kerr, and after about an hour on the phone with them, trying this and that, discover that the pin on the shaft that the arm sits on had sheared off. It must've taken a few castings for it to finally give, as the inside of the hole looked like somebody had tapped it. That would also give me the turbulence issue I'm sure. But that also explains why it was such a pain to get the arm off of the shaft. I got the impression this does not occur all that often, but after playing with the darn thing for three hours, it's up and spinning again.

In case you're wondering, switched abutment design from a custom waxed to a stock abutment.
So much easier.

Carol
 
Pronto

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I have started raising the burnout temp a little too when double casting to the gold abutment. That helped with miscast showing incomplete coverage of the gold abutment.
 
JohnWilson

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I have started raising the burnout temp a little too when double casting to the gold abutment. That helped with miscast showing incomplete coverage of the gold abutment.

You have to be carful with this as this can over expand the ring as well.

Truth is miscasts are rarely caused by too cold a ring but more because of improper burnout when it comes to "Casting to" another object. The non oxidizing metal needs to be at the proper casting temperature to have a good interface, but the investment needs to be pristine for optimal results. Anytime you burn out plastic/lexan/duralay or any pattern resin it needs to be staged to take stress off the mold from the material expanding as it burns.

We have found PD/Au based alloys seem to work the best for us for screw retained cases. When we are forced to do a wax and cast abutment we choose to use a predominately PD based Nobel alloy.

Truth is this technique for my lab is almost obsolete. Cad cam will virtually eliminate all but molar screw retained crowns.
 
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kcdt

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Truth is this technique for my lab is almost obsolete. Cad cam will virtually eliminate all but molar screw retained crowns.

No kidding, I used to be up to my eyeballs in UCLA type work, haven't touched one in years.
 
JohnWilson

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No kidding, I used to be up to my eyeballs in UCLA type work, haven't touched one in years.

Yes its amazing how technology has changed our industry. It would be fun to look 20 years in the future to talk to a new tech and tell them how archaic we were using a brush and powder to build restorations. He/she will think we were cave men.
 

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