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Abrasion and Etching Effects on Lithium Disilicate Strength
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vjau



Joined: 08 Jul 2009
Posts: 76

PostPosted: Sat Mar 08, 2014 4:01 am    Post subject: Abrasion and Etching Effects on Lithium Disilicate Strength Reply with quote

1441 Abrasion and Etching Effects on Lithium Disilicate Flexural Strength

Saturday, March 22, 2014: 9:30 a.m. - 10:30 a.m.
Location: Exhibit Hall AB (Charlotte Convention Center)
Presentation Type: Poster Session
Track: Clinician Track
T.S. MENEES1, V.K. KALAVACHARLA2, P. BECK2, D. CAKIR2, L.C. RAMP2, and J. BURGESS2, 1Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL, 2School of Dentistry, University of Alabama at Birmingham, Birmingham, AL
Objectives: Lithium disilicate is a glass-containing ceramic for all-ceramic restorations. During fabrication or before bonding to the preparation, alumina oxide abrasion or HF acid-etching may be used to create micromechanical retention. Few studies have investigated how HF etching or abrasion affects the flexural strength of lithium disilicate ceramics. This study measured and compared the flexural strength of e.max CAD following alumina abrasion at differing pressures and acid-etching at differing concentrations and times.
Methods: Bars of e.max CAD (9 groups of 10 - 22mm x 2.5mm x 2.5mm) were prepared; polished sequentially (180, 320, and 600 paper); and fired following manufacturer’s instructions. 4 groups were particle abraded (30µm alumina from 10mm at 8psi, 15psi, 30psi, or 45psi for 10s). 2 groups were etched with 5% HF (20s or 2 minutes). Two groups were etched with 9.5% HF (20s or 2 minutes). The control was polished and fired only (no treatment). Specimens were loaded using a three point flexural test to failure in an Instron (1mm/min crosshead speed). ANOVA and Dunnett’s t-test determined intergroup differences (p= 0.05).

Results: Compared to the control, the 15psi, 30psi, and 45psi abraded groups produced significantly lower flexural strengths (p<0.05). The 8psi treated group was not statistically different from the control (p>0.0Cool. The 5% and 9.5% HF etched groups were not significantly different from the control (p>0.05).
Group Mean Flexural Strength (MPa) Deviation (MPa)
Control 376.8 80
8 psi 305.3 29
15 psi 278.9 39
30 psi 240.6 31
45 psi 241.9 14
5% HF (20s) 313.7 62
5% HF (2min) 333.8 46
9.5% HF (20s) 303.5 39
9.5% HF (2min) 353.5 67

Conclusions: Alumina particle abrasion higher than 15psi significantly reduced e.max CAD flexural strength. HF etching is recommended to increase micromechanical retention and clean the intaglio surface of the restoration prior to bonding.
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john kanca



Joined: 14 May 2005
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PostPosted: Sat Mar 08, 2014 3:09 pm    Post subject: Reply with quote

10 seconds is a long time. The important parameter to measure for clinical appropriateness would be compressive strength. I am not familiar with any evidence of clinical disadvantage consequent to sandblasting.
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priior



Joined: 10 Feb 2009
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PostPosted: Sat Mar 08, 2014 4:15 pm    Post subject: Reply with quote

also, if 300 and 270 are not statistically different, it means there's a big standard deviation. im not sure 10 samples of each is enough.

moreover, a t test is a parametric test and to be able to compare 2 means it needs to assume the 2 populations are coming from normal distributions, to be able to assume that (central limit theorem) you need _AT LEAST_ 30 samples (if not more ) to be able to use the test.

they should have used a non-parametric test with such small samples, i wonder why they didnt!
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john kanca



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PostPosted: Mon Mar 10, 2014 6:52 am    Post subject: Reply with quote

What I take away from this study is that were I to place a bridge made of eMax I would not sandblast the connectors.

(I would not make a bridge out of eMax, BTW)
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john kanca



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PostPosted: Mon Mar 10, 2014 6:55 am    Post subject: Reply with quote

priior wrote:
also, if 300 and 270 are not statistically different, it means there's a big standard deviation. im not sure 10 samples of each is enough.

moreover, a t test is a parametric test and to be able to compare 2 means it needs to assume the 2 populations are coming from normal distributions, to be able to assume that (central limit theorem) you need _AT LEAST_ 30 samples (if not more ) to be able to use the test.

they should have used a non-parametric test with such small samples, i wonder why they didnt!


Strikes me as odd that 2 min of HF would result in a higher FS than 20 seconds.
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ilikecoffee



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PostPosted: Wed Mar 12, 2014 12:43 pm    Post subject: Reply with quote

Blasting weakens crowns is a logical conclusion. Further testing needed to confirm amount. Wheter or not clinically significant is dependent on may variables not possible to be included in test.
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scottie



Joined: 21 May 2005
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Location: Albuquerque NM

PostPosted: Wed Mar 12, 2014 10:40 pm    Post subject: Reply with quote

John, I note you say you would not make a bridge out of Emax. I made a maxillary one replacing the first bicuspid, if I'm remembering it correctly. Lab was okay with it too, but they would not make an Emax bridge replacing a molar. So far no problems
I do very few zirconium crowns. Initially it was Emax for bicuspids forward and zirconium for molars. Now I do Emax for all single units and occasionally I'll go zirconium for a molar where the patient is a heavy bruxer.
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vjau



Joined: 08 Jul 2009
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PostPosted: Thu Mar 13, 2014 5:06 pm    Post subject: Reply with quote

I think the main advantage of HF versus Sandblasting is control.
You must sandblast not too close, not too far, with the proper pressure, during the appropriate time.... HF 20 seconds is easy. I don't think Ivoclar is making millions selling the HF.
Btw i'm using both HF and Interface (i like the idea of an always fresh silane).
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Ekrause



Joined: 11 May 2005
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PostPosted: Fri Mar 14, 2014 11:56 am    Post subject: Reply with quote

ilikecoffee wrote:
Blasting weakens crowns is a logical conclusion. Further testing needed to confirm amount. Wheter or not clinically significant is dependent on may variables not possible to be included in test.


Ditto for HF etching. Wink
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john kanca



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PostPosted: Sun Mar 16, 2014 3:16 pm    Post subject: Reply with quote

ilikecoffee wrote:
Blasting weakens crowns is a logical conclusion. Further testing needed to confirm amount. Wheter or not clinically significant is dependent on may variables not possible to be included in test.


I disagree. A three point bending test is not clinically relevant for a single crown. Compressive strength is more appropriate. Three point bending is more appropriate for connectors on a bridge.
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john kanca



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PostPosted: Sun Mar 16, 2014 3:19 pm    Post subject: Reply with quote

scottie wrote:
John, I note you say you would not make a bridge out of Emax. I made a maxillary one replacing the first bicuspid, if I'm remembering it correctly. Lab was okay with it too, but they would not make an Emax bridge replacing a molar. So far no problems
I do very few zirconium crowns. Initially it was Emax for bicuspids forward and zirconium for molars. Now I do Emax for all single units and occasionally I'll go zirconium for a molar where the patient is a heavy bruxer.


I'm glad it's working for you, Scottie. How long has it been in the mouth and are we talking about a cuspid to bicuspid bridge?
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Ekrause



Joined: 11 May 2005
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PostPosted: Sun Mar 16, 2014 8:26 pm    Post subject: Reply with quote

john kanca wrote:
ilikecoffee wrote:
Blasting weakens crowns is a logical conclusion. Further testing needed to confirm amount. Wheter or not clinically significant is dependent on may variables not possible to be included in test.


I disagree. A three point bending test is not clinically relevant for a single crown. Compressive strength is more appropriate. Three point bending is more appropriate for connectors on a bridge.


Don't sandblast or HF etch the underside of bridge connectors!!!
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priior



Joined: 10 Feb 2009
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PostPosted: Mon Mar 17, 2014 5:40 am    Post subject: Reply with quote

the point remains, the performed statistical test is not appropriate for this dataset.

those numbers mean nothing.

i'm concerned tho that the SD is so high, those blocks are supposed to be pretty standard? why is there so much variation among them? is a lithium disilicate crown a hit and miss procedure?

or does the technique of applying HF or sandblasting have such a big effect?

both are concerning!
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ilikecoffee



Joined: 02 Mar 2010
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PostPosted: Tue Mar 18, 2014 11:27 am    Post subject: Reply with quote

I am still not sure what you disagreed with.
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scottie



Joined: 21 May 2005
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Location: Albuquerque NM

PostPosted: Wed Mar 19, 2014 10:38 pm    Post subject: Reply with quote

John
I am out of the office at the moment in Uganda.
I will check my records when I get back on the details of the E-max bridge.
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