Acrylic Casting Pressure?

[Didley]

As I said earlier, Ivocap is (or claims to be) different in that it cures different areas at different rates and therefore can claim this reservoir effect. (If you believe it) Other injection methods, I think, rely on compression to compensate for shrinkage, this is why I question the amount of pressure, is more better, 5-6 bar is very little. I believe the acrylic in a pack method would be at greater than 6 bar??????
The different color acrylics "trick" of the Ivocap demo can be explained away by the fact that when the color change is made pressure goes off, some acrylic goes back out the sprue and then goes back in when pressure is reapplied, But I'm not here to argue about a marketing trick

 

[hydent]

Just for the sake of conversation what do you think would happen if you processed a success flask in an Ivocap curing unit? I meen logically there is still plenty of acrylic in the sprue cavity to have the spring continue to press acrylic in, no?

 

[kcdt]

Better yet, Ill introduce you to a guy with a phd in polymer chemistry who says what you interpret is not the way it is. With that said, I will grill steaks or have dinner anytime, as long as we can avoid dental talk.

As was said before, injection is a good production tool, and the marketing of the idea has tons of money behind it. Which works for labs looking to piggyback on the marketing.

There are many ways to skin a cat, its all good as long as it gets skinned.

That is a very wise statement. I for one, appreciate how marketing can help us sell products, but marketing is still marketing in the end.

 

[kcdt]

Bart does have a point, but I better not go there. Your not saying you cant get a crystal clear egg using pack pressing are you? Porosity is something people who dont understand the materials get.

Absolutely correct. I saw at the maxillofacial meeting back in '04 (I think),some example of clear acrylic plates used for surgically closing defects in the skull. The size and shape of these required custom made flasks, but the technician compression molded his parts. CLEAR AS GLASS.
It's all about proper methodology.

 

[Didley]

Just for the sake of conversation what do you think would happen if you processed a success flask in an Ivocap curing unit? I meen logically there is still plenty of acrylic in the sprue cavity to have the spring continue to press acrylic in, no?

I'd think you'd have a normal "Success" denture, the Ivocap trick is in the flask design, it has isolation to slow the curing in the top of the flask(supposedly),as well as the water not covering the top of the flask.

 

[Brian Hyde]

I'd think you'd have a normal "Success" denture, the Ivocap trick is in the flask design, it has isolation to slow the curing in the top of the flask(supposedly),as well as the water not covering the top of the flask.

Ivocap is a great material I dont want you to think I am bagging on it.... So lets say you put the success flask not covering the top of the flask? Wouldnt the same results occur? I have had busy days in the lab where I was curing my dentrues for two hours in boiling water where I didnt have time to fill the boilout and wait for it to heat back up, The plungers were exposed and the dentures cured just fine.. I agree that the thought is good for marketing pruposes but dont believe its true..

 

[Didley]

I agree that the thought is good for marketing pruposes but dont believe its true..

Well, I tend to agree with you

So any thoughts on my original question, is there an optimal pressure, is more better, does acrylic dough compress at all past the point of excluding all the air?

 

[hydent]

I'd think you'd have a normal "Success" denture, the Ivocap trick is in the flask design, it has isolation to slow the curing in the top of the flask(supposedly),as well as the water not covering the top of the flask.

Not saying it's wrong because I don't know but I think the flask desing and metal plates may be a lot of hokus pokus that's just my opinion on that matter. I have said before that I think the Ivocap sysetem is great, but I don't buy into all of that jive about flask design. I think once the heat enters the denture in the flask it's doesnt matter how it is shaped or designed as long as the heat source is constant. I think if you found the right amount to submurge the flask you would have the same result. Like I said though that's just my theory It's not proven.

 

[araucaria]

Thanks Tom.

araucaria, do you realize in a standard hydraulic dental press, the mid range area where they recommend pressing a conventional press flask to, is around 100-180 bar. The 5-6 bar that pneumatic injection systems work on, you could almost push in with your fingers. It gives me doubts as to the advantage of injecting???

Any thoughts anyone!

25 BAR is 360 PSI
100 BAR is 1440 PSI !!

Try this link
Pressure Unit Conversion and Converter

hope you've got strong fingers

 

[Didley]

25 BAR is 360 PSI
100 BAR is 1440 PSI !!

Try this link
Pressure Unit Conversion and Converter

hope you've got strong fingers

Thanks araucaria, but my problem is my press gauge is in Kilograms, as in a weight measure not Kg/square cm or lb/ square inch. I don't think there is a conversion. The company web site says the green zone, between 4000 and 7000kg is the equivalent of 100- 180 bar, so that's what I'll have to go with. So if I want something like 6 bar as soon as the needle moves, I'm going to far.

 

[droberts]

Pack an egg Tom. Just show me how much dimensional change you have when you get done. Another example of how the flask is insulated. When I used to pack, I would place the flask in my Kavo boil-out for 8-10 minutes to soften the wax. With Ivocap, its 18-20 minutes to get the same effect. No, I am not saying its softening from the bottom up. Just the difference. The curing time for 1 case is 35 minutes. Bring a case over and I'll process it for you for 25 minutes and we'll break the case out. I'll let you tell me how it cured. I am the type of guy that likes to learn something everyday whether it be something even as simple as this. What am I missing here?

 

[araucaria]

Hi Didley - I have the very same press in my lab
I normally press up to 2.5 for first trial packing, then to 3 to 3.5 this is plenty.
Each unit is metric tonne. 3 is the setting for the Ivocap clamping unit.
Don't worry - go with your instincts.

 

[droberts]

As I said earlier, Ivocap is (or claims to be) different in that it cures different areas at different rates and therefore can claim this reservoir effect. (If you believe it) Other injection methods, I think, rely on compression to compensate for shrinkage, this is why I question the amount of pressure, is more better, 5-6 bar is very little. I believe the acrylic in a pack method would be at greater than 6 bar??????
The different color acrylics "trick" of the Ivocap demo can be explained away by the fact that when the color change is made pressure goes off, some acrylic goes back out the sprue and then goes back in when pressure is reapplied, But I'm not here to argue about a marketing trick

To correct you on the amount of acrylic that was removed when the injection tube was removed, was whatever the amount that is in the tube. It already had full pressure and had set for 5 minutes before removing. Not a trick, just the facts. The same would be as if you were packing a case and let it set for 5 minutes. The acrylic is stable enough but not cured that it is not going to move all that much.

 

[CYNOSURER]

Help me with my rudimentary grasp of physics.

Accepting that Ivocap does indeed heat from the bottom up due to the design of the flask, Physics tells us that ALL matter expands when heated. As the denture cures...bottom to top...shouldn't that expansion be pushing material back into the reservoir? Physics tells us that ALL matter contracts when cooling. Isn't this (as with casting metal) when the value of the reservoir is needed. And, isn't it too late for a denture that has been cured bottom to top to benefit from this reservoir?

Just trying to wrap my head around it. Thanks for bringing this up and your patience.

 

[kcdt]

I feel like this is a real to each his own kind of thing. The thing about working with resin is protocol, if you do your job properly, you get the results you're looking for.
If you really read the research literature on this, yes, injection molding has a statistically greater degree of accuracy (but so does autocure). The problem is that the differences are so small that clinical relevance is called into question in every study.
Add to the fact that all resins under go distortional strain, and that strain simply manifests in different manners when you use different processing methods and pretty soon you're chasing your tail.

 

[droberts]

The reservoir is also insulated. Like I said, its all on the amount of time. Leave it in the water bath too long, you can cure the hole tube of acrylic. I think you understand.
I'm am injecting a reline right now. Invested it directly in the flask, remove it and prep it, then inject, cure for 35 minutes /cool 40 minutes and break out. Nice thing about it, I can remove ans much material as I want and not worry about dimensional change over a lab /cold cure reline. This is a much better technique.

 

[JohnWilson]

Is that the normal time table for curing in IVOCAP Danny?

 

[Kreyer]

droberts is one of the best technicians in the US. The work I have seen from Dr. Bob Schneider's presentations is amazing!!

In regards to:
Compression (Pack and Press)...
Injection (Success)
Continuous Press Injection (Ivocap)

It is only through experience that one has the knowledge base to throughly discuss a material and technique. If one has personal experience with Ivocap then they have the knowledge to discuss advantages and disadvantages..If one does not have the personal experience of the three processing techniques above then they should be open to learning as much as possible so they can make an educated decision based on experience and knowledge.

Rob

 

[hydent]

droberts is one of the best technicians in the US. The work I have seen from Dr. Bob Schneider's presentations is amazing!!

In regards to:
Compression (Pack and Press)...
Injection (Success)
Continuous Press Injection (Ivocap)

It is only through experience that one has the knowledge base to throughly discuss a material and technique. If one has personal experience with Ivocap then they have the knowledge to discuss advantages and disadvantages..If one does not have the personal experience of the three processing techniques above then they should be open to learning as much as possible so they can make an educated decision based on experience and knowledge.

Rob

True!

 

[araucaria]

Help me with my rudimentary grasp of physics.

Accepting that Ivocap does indeed heat from the bottom up due to the design of the flask, Physics tells us that ALL matter expands when heated. As the denture cures...bottom to top...shouldn't that expansion be pushing material back into the reservoir? Physics tells us that ALL matter contracts when cooling. Isn't this (as with casting metal) when the value of the reservoir is needed. And, isn't it too late for a denture that has been cured bottom to top to benefit from this reservoir?

Just trying to wrap my head around it. Thanks for bringing this up and your patience.

science can be a bit of a brainstorm some days - try ice.
Also bring chemistry into the equation, this changes everything.
Ivocap has a small reduced temperature above the flask at the denture heels due to there being no insulation from the protective bubbles/balls, so during the initial temperature increase through the flask the last part to come up to the boil temperature is the sprue point. The injector unit also helps to dissipate heat into the atmosphere as it's a good heat conductor and the air supply is probably a low temperature too. It's no big deal. A similar point of interest is how refrigerators in stores can keep food cool and safe when there's no lid or door - what's going on there?