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Abrasion and Etching Effects on Lithium Disilicate Strength
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priior



Joined: 10 Feb 2009
Posts: 345

PostPosted: Fri Mar 21, 2014 5:14 am    Post subject: Reply with quote

ilikecoffee wrote:
I am still not sure what you disagreed with.


was this question directed to me?

if it was... Smile

The t-test that the person did is called a parametric test. it is called parametric because it needs the assumption of some parameters to be valid. In this case, the assumption is that the sampel follows a normal distribution (or a t-distribution more specifically, since we don't know the standard deviation)

you can assume your sample follows a normal distribution when you have at least 30 specimens, per group. You need more if your standard deviation is larger. (or less if you _know_ your sample comes from a normal distribution, which we rarely do) this is because of the "central limit theorem" which says no matter how your data is distributed, their means will follow a normal distribution if the sample is large enough (30+). this theorem is at the heart of statistical testing.

in this case, they're comparing groups on 10 specimen... and from the description it sounds like they have a high standard deviation (SD). when you;re comparing 2 groups of 10 specimens to see if their means are statistically similar or not, you can't use parametric testing (if you don't know they come from a normal distribution), you have to use non paramteric testing. (wilcoxon, rank test, rank sum test, etc..)

and when you use non-parametric testing with small samples, your confidence is way lower. all this to say, i wouldn;t put too much weight on the significance of those numbers Smile

(sorry for the pedantic post!)
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Nareg Apelian DMD
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ilikecoffee



Joined: 02 Mar 2010
Posts: 121

PostPosted: Mon Mar 24, 2014 11:41 am    Post subject: Reply with quote

Smile John disagreed .

I still don't know what either of you are disagreeing with.

It is easy to rip apart any study, and based on statistical empirical evidence it would be difficult to use some of Apex's materials.


Could you humor me and take the part of my statement you disagree with and your evidence to support it?
I would love to have evidence presented to me that blasting strengthens zirconium crowns through enhncement of bonding.
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priior



Joined: 10 Feb 2009
Posts: 345

PostPosted: Tue Mar 25, 2014 3:43 pm    Post subject: Reply with quote

ilikecoffee wrote:
...
It is easy to rip apart any study, ...


for what it's worth i'm not sure this poster project (probably by an undergrad?) would get published. so this is not a case of "we can rip apart any study"... i just don't think those numbers mean anything.

john is talking about compressive strength v/s tensile strength and what os more important for a single unit crown. what kind of evidence do you want to see? one that shows that compressive strength is more important than tensile strength for crowns? Smile
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ilikecoffee



Joined: 02 Mar 2010
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PostPosted: Wed Mar 26, 2014 11:11 am    Post subject: Reply with quote

It is being suggested that blasting weakens zirconia for years now. However, practioners feel the need to blast and use their cementatation procedure of choice with blasting. I would love to see the numbers verifying that this is the best way to in regards to strength rather than all out assault on the studies that suggest that blasting weakens zirconia. Rather that disproving the counter opinion , I would rather see proof of the opinion.
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Ekrause



Joined: 11 May 2005
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Location: I'm here now.

PostPosted: Thu Mar 27, 2014 7:46 am    Post subject: Reply with quote

Weakens how much? Clinical experience has shown that it doesn't matter. These aren't breaking, and I've done a few hundred in the last 4 years or so. Haven't lost one yet.
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john kanca



Joined: 14 May 2005
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PostPosted: Tue Apr 01, 2014 3:06 pm    Post subject: Reply with quote

ilikecoffee wrote:
It is being suggested that blasting weakens zirconia for years now. However, practioners feel the need to blast and use their cementatation procedure of choice with blasting. I would love to see the numbers verifying that this is the best way to in regards to strength rather than all out assault on the studies that suggest that blasting weakens zirconia. Rather that disproving the counter opinion , I would rather see proof of the opinion.


Several years ago I asked an IADR audience if anyone had every known of anything zirconia failing consequent to being sandblasted.

Crickets.
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ilikecoffee



Joined: 02 Mar 2010
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PostPosted: Wed Apr 16, 2014 11:02 am    Post subject: Reply with quote

Does anyone know anything about VOCO's zirconium bonding accentuater?
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scottie



Joined: 21 May 2005
Posts: 360
Location: Albuquerque NM

PostPosted: Wed Apr 16, 2014 11:53 pm    Post subject: Reply with quote

John
I finally found the chart on the Emax bridge I did.
It was a 5X7 bridge on a 90 yo patient. Yes I know what you're thinking. Doesn't have to last long! She's a fairly healthy patient and may live to 100.
She had a PFM bridge that broke off with some of the teeth inside it. I did not want to extract and do a partial and she did not want that either.
I prepared the teeth that were left, no endo on either, but I don't think there is much pulp tissue anyway, and bonded an Emax bridge with Panavia.
Placed it 8/10/13 and so far so good.
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john kanca



Joined: 14 May 2005
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PostPosted: Tue Apr 22, 2014 8:41 pm    Post subject: Reply with quote

scottie wrote:
John
I finally found the chart on the Emax bridge I did.
It was a 5X7 bridge on a 90 yo patient. Yes I know what you're thinking. Doesn't have to last long! She's a fairly healthy patient and may live to 100.
She had a PFM bridge that broke off with some of the teeth inside it. I did not want to extract and do a partial and she did not want that either.
I prepared the teeth that were left, no endo on either, but I don't think there is much pulp tissue anyway, and bonded an Emax bridge with Panavia.
Placed it 8/10/13 and so far so good.


Keep us posted! Good luck with it!
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