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Roughness and porcelain IMPORTANT
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john kanca



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PostPosted: Mon Jan 05, 2009 1:40 pm    Post subject: Roughness and porcelain IMPORTANT Reply with quote

Roughness weakens porcelain.


That includes sandblasting, burs and HF etching. It affects low fusing porcelains more than high fusing porcelain.

I am headed home, and I'll post these articles when I get home. They're very interesting.
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Mark J Fleming DDS



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PostPosted: Mon Jan 05, 2009 2:53 pm    Post subject: Reply with quote

Im curious how this affects the sandblasting before Interface. Thanks Cool
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Pav



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PostPosted: Mon Jan 05, 2009 3:52 pm    Post subject: Reply with quote

Mark J Fleming DDS wrote:
Im curious how this affects the sandblasting before Interface. Thanks Cool


Echo that! Waiting for updated protocol Cool
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Howardmg



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PostPosted: Mon Jan 05, 2009 5:53 pm    Post subject: Reply with quote

Does the increase in bond strength due to sandblasting offset the weakening of the porcelain? Or in other words does the bonding increase the strength?
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john kanca



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PostPosted: Mon Jan 05, 2009 7:20 pm    Post subject: Reply with quote

Dent Mater. 2000 Nov;16(6):381-8.
The influence of surface roughness on porcelain strength.
de Jager N, Feilzer AJ, Davidson CL.
ACTA, Department of Dental Materials Science, Louwesweg 1, 1066 EA Amsterdam, The Netherlands.
OBJECTIVES: In order to adjust occlusion, the functional surfaces of porcelain restorations are often ground and mechanical machining is even an essential part of the CAD-CAM process for these restorations. The aim of this study was to investigate the influence of the finishing procedures on the biaxial flexure strength of four commercial porcelains. METHODS: Four commercial porcelains of which two are used for metal-ceramic restorations (Flexo Ceram Dentine and Vita VM K68) and two for veneers and inlays (Duceram LFC Dentine and Cerinate BODY) are used in this study. For each porcelain, sixty discs (ě = 22 mm, h = +/- 2.0 mm) were produced using twelve different finishing procedures. Twenty discs were left untreated, twenty discs were milled, using a high-speed diamond disc, and twenty discs were machined in a high-speed grinding/polishing device. Half of the samples were glazed. In each of these six groups, half of the samples were stored for 16 h at 80 degrees C in a 4% acetic acid solution. The biaxial flexure strength was determined using the ball-on-ring method. In each group the roughness of the surface was determined and examined via SEM. RESULTS: With the exception of Flexo Ceram Dentine, a significant correlation was found between the roughness of the surface and the biaxial strength: the smoother the surface, the stronger the sample. The differences in biaxial strength may be attributed to the stress concentration of an applied load due to the roughness of the surface caused by mechanical finishing or chemical action. The fact that the strength of Flexo Ceram Dentine was not affected by the different surface treatments is probably due to the size of the leucite particles, which apparently induce more stress concentration than the surface flaws and the roughness of the surface. SIGNIFICANCE: It was concluded that surface roughness determines the strength of a porcelain material, except where the inner structure of the material causes greater stress concentration than that caused by the combination of surface roughness and surface flaws.
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john kanca



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PostPosted: Mon Jan 05, 2009 7:21 pm    Post subject: Reply with quote

J Dent. 2004 Feb;32(2):91-9. Links
Effect of sandblasting, grinding, polishing and glazing on the flexural strength of two pressable all-ceramic dental materials.
Albakry M, Guazzato M, Swain MV.
Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, Suite G11, National Innovation Centre, Australian Technology Park, 1430, Eveleigh, NSW, Australia. albakrym@hotmail.com
OBJECTIVES: During laboratory fabrication procedures and/or clinical adjustments, pressable materials: IPS Empress and Empress 2, may be ground, polished or sandblasted. These treatments may affect their strength by introducing microscopic flaws and defects. This study investigates the effect of these procedures on the mean flexural strength of these materials. METHODS: One hundred and forty disc specimens (14mmx1 mm) of IPS Empress and Empress 2 were prepared, and divided into seven groups of 20 specimens for each material. Groups were untreated, polished, polished and glazed, ground, ground and glazed, sandblasted, sandblasted and glazed. Surface roughness, mean biaxial flexural strength and Weibull modulus were appraised, and a scanning electron microscope was used to describe surface features. Statistical significance among groups of population was analysed using one-way Anova and Tukey's multiple comparison tests. RESULTS: Untreated and sandblasted groups showed significantly the highest roughness values, and polished the lowest for each material (p<0.05). Ground groups showed significantly lower roughness values than the sandblasted groups, and significantly higher roughness than the polished groups for each material (p<0.05). Polished groups for each material demonstrated significantly the highest mean flexural strength values (p<0.05). No significant difference in the mean strength values was found between untreated, sandblasted and ground groups for each material (p>0.05). Heat treatment had no effect on roughness or strength values of all treated groups of both materials. The Weibull modulus values for both materials varied with different treatments. They showed higher values for polished and untreated groups, and lower values for ground and sandblasted groups. CONCLUSIONS: Surface roughness may not be the only feature that determines strength. Other issues such as porosity, microstructural residual stresses, surface and bulk defects may also be pertinent.
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john kanca



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PostPosted: Mon Jan 05, 2009 7:21 pm    Post subject: Reply with quote

Dent Mater. 2007 Nov;23(11):1332-41. Epub 2006 Dec 27. Links
The impact of modifying alumina air abrasion parameters on the fracture strength of a porcelain laminate restorative material.
Addison O, Marquis PM, Fleming GJ.
Biomaterials Unit, University of Birmingham School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK. owen.addison@virgin.net
OBJECTIVES: The modification of the "fit" surface of porcelain laminate veneer restorations in order to improve adhesion prior to cementation is often indiscriminate. As a consequence, the surface flaw distribution which is implicated in the probability of failure of the restoration is likely to be dramatically modified. The purpose of the current study was to examine the impact of different air abrasion surface treatments on the bi-axial flexure strength and surface roughness of a porcelain restorative material. METHODS: Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were alumina abraded with three different grades of alumina particle (25, 50 and 110 microm), utilizing two different air stream pressures (35 and 70 psi) and two distinct angles of incidence of particle delivery (45 degrees and 90 degrees ). Mean bi-axial flexure strengths, standard deviations, the associated Weibull moduli (m) and characteristic stress were determined using bi-axial flexure (ball on ring). RESULTS: A univariate general linear analysis of means revealed a significant difference between the mean bi-axial flexure strength values of the control group and those of groups subjected to alumina particle air abrasion. Further significance (P<0.05) was discovered with the impact of alumina particle size and the interaction between particle size and angle of incidence of particle delivery. The reliability of the fracture strength data generally improved when 50 micron alumina particles were used whereas discontinuities existed at lower strength values when 25 and 110 microm alumina particles were employed. CONCLUSIONS: Alumina particle air abrasion has a significant degradative effect on the bi-axial flexure strength of the porcelain disc-shaped specimens. Variation of alumina size, delivery pressure and angle of particle delivery all impacted on the degree of strength reduction and the shape of the survival probability distributions. It is suggested that alumina particle air abrasion acts to remove/modify the initial flaw distribution replacing it with flaws of differing geometry and stability. The premature failure of porcelain laminate restorations may be markedly influenced by alumina particle air abrasion depending upon the size and distribution of the crystalline phase present in different dentine porcelains materials used in construction of the restoration.
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john kanca



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PostPosted: Mon Jan 05, 2009 7:23 pm    Post subject: Reply with quote

Dent Mater. 2007 Apr;23(4):461-8. Epub 2006 Apr 18. Links
The impact of hydrofluoric acid surface treatments on the performance of a porcelain laminate restorative material.
Addison O, Marquis PM, Fleming GJ.
Biomaterials Unit, University of Birmingham, School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK. owen.addison@virgin.net
OBJECTIVES: Hydrofluoric (HF) acid etching increases the bond strength between composite resin and porcelain surfaces and has been advocated as a pre-cementation technique for ceramic restorations. The internal surface flaw distribution which is implicated in the premature failure of ceramic restorations is modified by the etching process and little agreement exists amongst researchers as to the appropriate etching regime. The purpose of the current study was to examine the impact of HF acid concentration and etching time on the performance of a low fusing feldspathic porcelain. METHODS: Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were etched with HF acid of three different concentrations (5, 10 and 20%) and for three different etching periods (45, 90 and 180s). Mean flexure strengths, standard deviations and the associated Weibull moduli (m) and characteristic stress (sigma(0)) were determined using bi-axial flexure (ball on ring). Contact profilometry was utilised to characterise the roughness of the etched porcelain surfaces. RESULTS: A univariate general linear analysis of means revealed a significant reduction in the mean strength values of the as-fired control compared with groups subjected to HF acid etching. Further significance (P<0.05) was discovered with the impact of acid concentration. Altering etching time also resulted in changes in the reliability of the fracture strength data. Contact profilometry demonstrated an increase in surface roughness following HF acid etching and an increase in roughness associated with increasing HF concentration. CONCLUSIONS: Etching of feldspathic porcelain is a dynamic process and the impact is dependent on substrate constitution, surface topography, acid concentration and etching time. A significant reduction of the flexural strength of a low fusing feldspathic porcelain has been demonstrated to result from etching and clear evidence exists that the nature of surface flaw modification is a function of etching time and HF acid concentration. Favourable combinations of HF acid concentration and etching time have been identified which enhance the reliability of the porcelain utilised although variability in clinical technique will result in the reduced reliability of porcelain laminate restorations in function.
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john kanca



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PostPosted: Mon Jan 05, 2009 7:24 pm    Post subject: Reply with quote

Howardmg wrote:
Does the increase in bond strength due to sandblasting offset the weakening of the porcelain? Or in other words does the bonding increase the strength?


To a degree, but it depends on the porcelain. The lower the flexural strength, the greater the compromise.
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john kanca



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PostPosted: Mon Jan 05, 2009 7:29 pm    Post subject: Reply with quote

Here's my take:

The lower the flexural strength, the greater the compromise.

Smooth is better than rough.

For porcelain veneers, don't allow the lab to do ANY etching. They tend to do ten minute etch periods. If you insist on etching, don't use more than 5% for two minutes or 9.6% for one minute.

Sandblast with no more than 27 micron, consider using bicarb for cleaning the inner surfaces of ceramics.

Use INTERFACE, now more than ever. Surpass 3 is better with Interface than Simplicity 2.
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Pav



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PostPosted: Tue Jan 06, 2009 5:03 am    Post subject: Reply with quote

Bicarb instead of aluminium oxide? Would it be best to not sandblast at all?
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jasonl



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PostPosted: Tue Jan 06, 2009 7:20 am    Post subject: Reply with quote

So we are/were sandblasting to roughen to improve the bond?!
and we were etching for the same reason but also to help remove any residue from fabrication or tryin??!

Assuming the lab did not etch - will we want to just scrub with isopropyl alcohol? Sandblast with fairy dust?
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john kanca



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PostPosted: Tue Jan 06, 2009 8:12 am    Post subject: Reply with quote

Pav wrote:
Bicarb instead of aluminium oxide? Would it be best to not sandblast at all?


With low fusing ceramics, one could make that argument.

It makes me wonder if this is related to the occasional crack that develops in low-fusing veneers after placement. Labs tend to etch everything for ten minutes and that could be consequential, especially if thin.
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Pav



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PostPosted: Tue Jan 06, 2009 8:51 am    Post subject: Reply with quote

What is classified as a low fusing porcelain?

Thanks!
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john kanca



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PostPosted: Tue Jan 06, 2009 9:03 am    Post subject: Reply with quote

jasonl wrote:
So we are/were sandblasting to roughen to improve the bond?!
and we were etching for the same reason but also to help remove any residue from fabrication or tryin??!

Assuming the lab did not etch - will we want to just scrub with isopropyl alcohol? Sandblast with fairy dust?


Sandblasting also cleans up. Both improve retention, yet both can compromise strength. The lower the flexural strength, the greater the compromise.
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