Zirconia Implant question

[subrisi]

I had to send a case out to another lab to get a scan and mill for a Zirconia abutment on a Neoss implant. Atlantis don't do them. I sent the models and naive as I am ( or is is ignorant to cad/cam systems?),I assumed they scan the models (both) and the interface and design an abutment. I requested images before milling. All I got is this.
I have no idea how it fits between the ajacent teeth and the opposing. The surface is all bumpy and there is no defined margin. I learned once it is sintered, you do not grind on it anymore. When I complained to the milling center and told them to redo it, they told me that they will make it smooth. when I asked at what state they said after sintering. I don't like that. They promised me that after grinding they fire it again and "make it stronger". What the heck does that mean?
Is there soemone out there who can explain this. What is OK and what isn't?

 

[trianglej]

What we get after a design is a rough image that has to compensate for the size of the burs used. Some areas may get over milled to allow for this. Once the mill is accomplished and the unit is removed from it's base, you can do some minor adjustments to remove sprue attachment and/ or mill marks with a diamond bur or impregnated silicone wheel to smooth it out being that the material is the consistency of a block of chalk. then it should be cleaned prior to sintering. after sintering the zirconia may be adjusted minimally with a diamond bur and lots of water( a "presto aqua" works great for this) and avoiding the "sparking" that may occur( which is when the fracturing occurs). There may be a bit of surface texture left below the margin line of an abutment that can be "polished" with Brassler Dialite wheels. Green - is coarse and will do some reduction. Blue- is medium and Pink-is high lustre. You may have had to adjust a zirconia coping prior to layering porcelain, after which Ivoclar suggests a "healing" or regeneration cycle before applying the zirliner.
The key question is what is the company's guarantee and failure policy?
I don't have any fear of adjusting zirconia that is sintered as long as I go "low and slow" with plenty of water to keep it cool.

 

[smile4me]

Zirconia has to be fired after it has been grinded on to strengthen it.

 

[Rex Kramer]

Well to plug Bob's company I just outsourced my first design/mill custom abut to him (i usually do my own on the piccolo but Im becoming more and more anti Nobel Biocare and I didnt have the astrotech blank anyways) and they send out a video of the case for you to see and approve. Great idea IMHO.... specially on a big funky bridge I had him do..... ortho via prosthetics lol.... check out his site hes got education stuff too.... C.A.P.

rex
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[subrisi]

So how do I know that there was no sparking on the abutment when the tech is done grinding on it? I am forced to buy a product that might not be treated the correct way. That doesn't make me feel good. Even if I get a warranty on the abutment. I still have to redo the crown for free. Atlantis is such a no brainer. Great warranty and never a dispute if something has to be redone.

 

[CadCamTech]

So how do I know that there was no sparking on the abutment when the tech is done grinding on it? I am forced to buy a product that might not be treated the correct way. That doesn't make me feel good. Even if I get a warranty on the abutment. I still have to redo the crown for free. Atlantis is such a no brainer. Great warranty and never a dispute if something has to be redone.

There is no way to tell if improper techniques were used, but if you do not trust the milling center you sent the work to you should find another. There are plenty of reputable ones out there!

And the theory about the second firing cycle for Zr is that grinding on sintered Zr creates ares of stress concentration that could be future sites of crack propagation and by bringing the Zr back up to peak temp again the crystal structure "reorganizes" and releives the stress concentrations.

 

[DMC]

Re-fire the Zirconia? Isn't it already cemented to the Ti base at this point guys? That's not necessary if you just gently grind a little on the Zirconia.

I grind on post sintered Zirconia all the time! How do you think margins get finished?

I also polish Zirconia on abutments, under the margin. Not on the cemented areas of course. Just what areas of Zirconia touch soft tissue.

So what? I think it is the right thing to do. Machines are not perfect.

If I think the margin could be a little lower, or pulled in a little once I see it in the model...I'll fix it!

You don't??? You just leave the rough machined surface-finish?

I at least always polish the sub-gingival areas...even with raw Zirconia.

 

[subrisi]

I also polish the area below the margin, but this does not create much stress. I never touch an abutment with a burr. I use Atlantis for all my abutment needs, just this one had to go somewhere else, because Atlantis does not do Neoss. I make sure the design is perfect before I approve any design and since Atlantis has an edit button, I can now do my own changes. I only once had a problem with the margin placement and they re designed and milled a new one for no additional costs.

 

[.:FIN:.]

I'm little confused about the "healing" firing or second sintering firing after I have touched zr with burr. Does anyone have any resarch about the benefits of this second firing, or is it just one of those things that you (if you so) because you have told so and you have always done it?

 

[k2 Ceramic Studio]

I'm little confused about the "healing" firing or second sintering firing after I have touched zr with burr. Does anyone have any resarch about the benefits of this second firing, or is it just one of those things that you (if you so) because you have told so and you have always done it?

Do you have an Ivoclar press furnace? If so you will find the program in it, it is a regeneration firing, once you have ground the Zr you physically change the properties of it in that area the same as if you sandblast it! A RGF must be accomplished to return the zirconia to the tetragonal phase, (to return it to its unchanged state it needs to go on a regeneration firing). Its not done for fun it is done to protect the substructure. There is a lot of science behind this: JUST GOOGLE IT!

 

[Mark Jackson]

So how do I know that there was no sparking on the abutment when the tech is done grinding on it? I am forced to buy a product that might not be treated the correct way.

If you do not trust the vendor, change labs. Nobody is forcing you to do anything. Trust is the key to everything. Look for a lab witrh an ISO or DAMAS certification.

 

[.:FIN:.]

Do you have an Ivoclar press furnace? If so you will find the program in it, it is a regeneration firing, once you have ground the Zr you physically change the properties of it in that area the same as if you sandblast it! A RGF must be accomplished to return the zirconia to the tetragonal phase, (to return it to its unchanged state it needs to go on a regeneration firing). Its not done for fun it is done to protect the substructure. There is a lot of science behind this: JUST GOOGLE IT!

I know the idea behind the regeneration fire, just wanted to know more about it and thought that this could be right place to find it. I'm not native English speaker, so scientific text is sometimes hard for me to understand in English, and there is not that much information about it in Finnish.

It would be nice to see some research about zr strength with the regeneration fire and without it, how it influence to the structure. I'm sure that someone have test it, but I would like to see the results.

 

[paulg100]

Basically the idea that a regen fire strengthens the zr is kinda BS. All it does is re-stabilize it at room temperature, as you will de-stabilize from flash heating when you grind.

Regen firing will NOT heal cracks caused by grinding.

go to the ivoclar website and download the scientific documentation for zircad.

It explains the stage transformation the zr goes through when sintering and will give you a better understanding of what the regen fire does.

Edit: sorry Pete, typed this before i read your post, you already said the same thing

 

[.:FIN:.]

I'm sorry to bother and this feels stupid, but I can't find the scientific documentation about zircad... I think it should be in this list...

Scientific Documentation

but it isn't...

 

[.:FIN:.]

I will answer to myself regarding to study I found:

"Even though many authors have showed that annealing of surface treated zirconia leads to a reduction of its flexural strength, several manufacturers recommend a ―Regeneration firing‖ in case of a surface modification of the material after sintering (for example Vita at 1000°C for 15 min; Ivoclar Vivadent 55 1050°C for 15 min). This firing is supposed to prevent the tension, which is created between the frame and the veneering ceramic due to the alteration of the CTE of the monoclinic Y-TZP (Vita Zahnfabrik, 2004; Ivoclar-Vivadent, 2008).

Nevertheless this recommendation should be seen critically, as the heat treatment of Y-TZP also in temperatures below 1000°C and independent of the holding time leads to a reverse transformation and the release of the compressive stresses (Guazzato et al., 2005b),which no longer counteract the flaws caused by the surface modification, thus lowering the strength of the material (Kosmac et al., 1999; Kosmac et al., 2000; Sundh et al., 2005; Guazzato et al., 2005b). (source:http://deposit.ddb.de/cgi-bin/dokserv?idn=1005346828&dok_var=d1&dok_ext=pdf&filename=1005346828.pdf)"

In that same study it is told that there are several studies about what treatment is good for zr and what is not. Very confusing...