Zirconia degrading in the oral environment

[Ken Knapp]

Respectfully, I have spoken with many ceramic engineers that all work for zirconia manufacturers. All have said the HT 1100 MPa generation materials do loose flexural strength over time. Here is a published article that confirms this notion. Interesting, 3M zirconia was one of the sample materials used in the study.
http://www.sciencedirect.com/science/article/pii/S0022391312601668
Please note, in this study there was no longer term data that related to 5 years but the degradation was still significant.

I don't believe the "steam" test is an accepted accelerated long term degradation test applicable to the oral environment or that this Scientdirect publication was peer reviewed. How many of the patients would survive with steam directed in the oral cavity, 0 patients would survive more than a day or two??

 

[grantoz]

all the steam test shows is if you treat the material badly enough it gets weaker in five years with that test all our dental materials will fail and the zombie apocalypse will start. the robots will be screwed as well.

 

[JMN]

all the steam test shows is if you treat the material badly enough it gets weaker in five years with that test all our dental materials will fail and the zombie apocalypse will start. the robots will be screwed as well.

I'm seeing this little yellow guy screaming "A, U, over 'ere."

 

[Car 54]

I don't believe the "steam" test is an accepted accelerated long term degradation test applicable to the oral environment or that this Scientdirect publication was peer reviewed. How many of the patients would survive with steam directed in the oral cavity, 0 patients would survive more than a day or two??

I was wondering about that, too. It seemed like they were trying to accelerate the the study by using a much higher temp than the normal oral environment,
how realistic can that be? Standard industrial ceramic aging conditions? What about normal oral conditions?

Taken from the link: http://www.thejpd.org/article/S0022-3913(12)60166-8/abstract?cc=y=

Experimental specimens were artificially aged at standard autoclave sterilization conditions,134°C at 0.2 MPa (n=5 per group at 50, 100, 150, and 200 hours) and standard industrial ceramic aging conditions, 180°C at 1.0 MPa (n=5 per group at 8, 16, 24, 28, and 48 hours)

If the normal body temp is 98.6f and this study shows 134c=s 273f (~3x normal body temp) and 180c=s 356f in an accelerated study, in that case, can't we multiply this study by 3 and worry about it in 15 years (5 being the most used baseline number)?

Didn't Ivoclar come out with (I still have the letter) that their research showed emax was actually stronger than they thought. That with all the restorations placed over the years, that emax at 1mm was actually around 500mpa, compared to 400mpa @ 8/10ths? So even though things naturally degrade and decay over time, it doesn't sound like it's going to be a issue if we're using good zirconia form reputable vendors and using it with good and common sense protocols?

 

[grantoz]

nailed it car 54. i had a conversation with a prosthedontist who was sponserd by a zi manufacturer his tests showed that there was no degradation in his companies Zi super trans all the way to old school layered zi opaque .I said thats cool good news when i asked did he test Zirkon Zahn prettau as everybody on this site knows that im a big fan of his response yes and it wasnt nearly as good as his companies because it showed degradation using artificial ageing of the equivalent of 75years it just starts to get silly after a while.

 

[CoolHandLuke]

they would use autoclave baseline to get degradation numbers and then adjust the equations using the acceleration factors as determined from the autoclave - and arrive at 5 years.

this ensures that their numbers arent affected by bacteria. essentially ideal conditions.

at 98f the specimens would still be affected by bacterial cultures so data would be erratic and not reproduceable.

 

[grantoz]

either way its misleading therefor shouldnt be taken as gospel or should be if your a fundamentalist .

 

[Sda36]

Danger Will Robinson!

How'd ya know??? That rotten Uncle again[emoji15]

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[Sda36]

How'd ya know??? That rotten Uncle again[emoji15]

Sent from my LG-H812 using Tapatalk

 

[BobCDT]

In science we must speed up studies to determine if there are changes that will take place. I'm not in a position to argue the testing process. No way does industry develop a new product and wait 5-10 years to obtain test results. What's really important here, if the material starts out at 1000 MPa and ends up in teh 600 MPa range, this is still 50% stronger than e.max. So there will definitely be huge numbers of success cases in spite of long term degradation. BTW, e.max has a 5 year 30% degradation and it seems to be working out well past this time frame. So when bonding emax 280 MPa seems to be OK.

 

[Car 54]

In science we must speed up studies to determine if there are changes that will take place. I'm not in a position to argue the testing process. No way does industry develop a new product and wait 5-10 years to obtain test results. What's really important here, if the material starts out at 1000 MPa and ends up in teh 600 MPa range, this is still 50% stronger than e.max. So there will definitely be huge numbers of success cases in spite of long term degradation. BTW, e.max has a 5 year 30% degradation and it seems to be working out well past this time frame. So when bonding emax 280 MPa seems to be OK.

Thanks Bob, for taking our back and forth here in stride and your helpful posts, links and insights. There is a science and real numbers to it all, that has to be considered.
I'm going to the MN dental meeting in a couple of weeks, and will be going to Rella Christiansen's lecture. I'll ask her if CRA is keeping up with this, and her thoughts, and if she has anything relevant to say or add to this discussion, I'll post it here.

 

[Car 54]

I was able to ask Rella the question about degradation of zirconia before her lecture started. She seemed a bit puzzled by what I asked, as far
as some of the higher numbers posted here of zirconia degradation, and of even emax degrading a bit over time. That she hadn't heard of the higher numbers,
but that she knew of degradation and would talk about it.

The degradation she knew about, and did have research on was layering porcelain "crumbling", degradation.
That since most ZI layering porcelains don't have lucite in them, for strength, that they over time they were crumbling. That's why Noritake
CZR Press has had such good success in their studies, is that Noritake somehow was able to add 9% lucite into the press material (let alone it's more homogeneous and denser due to it being a ingot and pressed, my thoughts). That the issue with lucite in zi layering porcelain is that the CTE changes, and that's why it's not used in zirconia layering porcelain.

They had started or were starting research on CubeX, Zenostar, Zirlux 16, Katana STML, about 8-10 zirconias including Bruxzir Now, but at that point the slides and her highlighting which ones they had started on, or were starting on, was getting to be a blur

 

[Sda36]

I was able to ask Rella the question about degradation of zirconia before her lecture started. She seemed a bit puzzled by what I asked, as far
as some of the higher numbers posted here of zirconia degradation, and of even emax degrading a bit over time. That she hadn't heard of the higher numbers,
but that she knew of degradation and would talk about it.

The degradation she knew about, and did have research on was layering porcelain "crumbling", degradation.
That since most ZI layering porcelains don't have lucite in them, for strength, that they over time they were crumbling. That's why Noritake
CZR Press has had such good success in their studies, is that Noritake somehow was able to add 9% lucite into the press material (let alone it's more homogeneous and denser due to it being a ingot and pressed, my thoughts). That the issue with lucite in zi layering porcelain is that the CTE changes, and that's why it's not used in zirconia layering porcelain.

They had started or were starting research on CubeX, Zenostar, Zirlux 16, Katana STML, about 8-10 zirconias including Bruxzir Now, but at that point the slides and her highlighting which ones they had started on, or were starting on, was getting to be a blur

Thanks for the report Car 54!![emoji5]

 

[BobCDT]

Hi,
I just found a study done with 3M on Lava zirconia. Here is the conclusion which claimed 30% degradation.

5. Conclusions;
The Y-TZP Lava (3M-ESPE) dental ceramic was susceptible to hydrothermal degradation when exposed to water steam at 140 C in vitro, despite the presence of Al2O3 in its composition. The t–m transformation followed a nucleation-and-growth kinetic, with predominance of the nucleation process. The transformation took place in a subsurface layer of 6 lm. Hydrothermal degradation resulted in a deterioration of the mechanical properties, with a 30% reduction of Young’s modulus and hardness. A strong correlation was found between the increasing monoclinic fraction and the decline in mechanical properties. Hence the emergence of the monoclinic phase and associated microcracking were the most likely cause for the degradation of mechanical properties.

Keep in mind 3M was involved in this study and had obvious interest in keeping the percentage of degradation as low as possible.

You can read the full study here.
http://campus.hesge.ch/nano/Files/14___acta_biomaterialia.pdf

 

[Car 54]

Hi,
I just found a study done with 3M on Lava zirconia. Here is the conclusion which claimed 30% degradation.

5. Conclusions;
The Y-TZP Lava (3M-ESPE) dental ceramic was susceptible to hydrothermal degradation when exposed to water steam at 140 C in vitro, despite the presence of Al2O3 in its composition. The t–m transformation followed a nucleation-and-growth kinetic, with predominance of the nucleation process. The transformation took place in a subsurface layer of 6 lm. Hydrothermal degradation resulted in a deterioration of the mechanical properties, with a 30% reduction of Young’s modulus and hardness. A strong correlation was found between the increasing monoclinic fraction and the decline in mechanical properties. Hence the emergence of the monoclinic phase and associated microcracking were the most likely cause for the degradation of mechanical properties.

Keep in mind 3M was involved in this study and had obvious interest in keeping the percentage of degradation as low as possible.

You can read the full study here.
http://campus.hesge.ch/nano/Files/14___acta_biomaterialia.pdf

It sounds to me like TRAC (Rella's research group) and CRA needs to start looking into this more than they have, or sounds like, haven't been.

 

[BobCDT]

One more note, These studies seem to conclude that the crystal size of the sintered restoration makes a big difference in the amount of degradation that occurs. Large crystal structures will degrade more. A 50 degree too hot furnace will result in enlarged crystal structure. 100 degrees is a massive increase in crystal size. That said, I think the accuracy of sintering temps and sintering furnace are critical to getting best results. I know many furnaces do drift up over time. We should calibrate our furnaces often and use quality furnaces and materials.

 

[Car 54]

One more note, These studies seem to conclude that the crystal size of the sintered restoration makes a big difference in the amount of degradation that occurs. Large crystal structures will degrade more. A 50 degree too hot furnace will result in enlarged crystal structure. 100 degrees is a massive increase in crystal size. That said, I think the accuracy of sintering temps and sintering furnace are critical to getting best results. I know many furnaces do drift up over time. We should calibrate our furnaces often and use quality furnaces and materials.

She also mentioned Glidewell and one other company buys direct from Tosoh, a pure re-milled into a finer grained zirconia, and thus it's denser and it wears
2 times faster than enamel (Bruxzir original, high strenght stuff).

 

[Sda36]

One more note, These studies seem to conclude that the crystal size of the sintered restoration makes a big difference in the amount of degradation that occurs. Large crystal structures will degrade more. A 50 degree too hot furnace will result in enlarged crystal structure. 100 degrees is a massive increase in crystal size. That said, I think the accuracy of sintering temps and sintering furnace are critical to getting best results. I know many furnaces do drift up over time. We should calibrate our furnaces often and use quality furnaces and materials.

Thanks Bob and agree! Have some Orton Temp Tabs arriving tomorrow. These can be placed with your work in the dish to test your peak temp. The company said that the rings were not as pure and could actually contaminate neighboring units if fired together.

 

[BobCDT]

Many disc manufacturers buy powder from Tosoh. Tosoh is a leader and there powder is more expensive than others. You will probably not find Tosoh powders in the less expensive sub $100 discs. Today, there are a lot of inferior powders in our market. It would be really interesting to see the same studies done with these low grade materials.

 

[Car 54]

Many disc manufacturers buy powder from Tosoh. Tosoh is a leader and there powder is more expensive than others. You will probably not find Tosoh powders in the less expensive sub $100 discs. Today, there are a lot of inferior powders in our market. It would be really interesting to see the same studies done with these low grade materials.

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