Help with micro porosity in ceramic

[paulg100]

Finally found the time to post about something ive been having problems with for a while.

im getting issues with mico porosity in my ceramic at the minute and i cant for the life of me get it sussed.



Here you see the issue, the little pits.

Seems to be more of a problem with emax ceram and when doing a 2 stage build technique. If i fire a crown in one bake its not an issue.

So things ive tried so far:

Things that dont help
Condensing - didnt help
Drying technique, ie blotting with tissue or using warm air - didnt help
Build liquid vs distilled water - didnt make any difference
different build liquids - didnt make any difference
painting stain liquid onto the first build before doing the enamel layer - didnt help
mixing a drop of stain liquid into the ceramic - didnt help
checked furnace ie vacuum etc - all working fine.
reduce temp of vacuum cut off - didnt help.

Things that do help
mixing 5-10% low fusing into the enamel ceramic - Helps but is a pain in the butt to do this when a crown has several different enamels.
Increase firing temp - helps but then rounds detail out (firing at 740 at the minute)
using a 1 stage build technique - did help... but crazy difficult and inconsistent with complex builds

The annoying thing is that some crowns come out great and others not so, and i cant nail down whats causing the variable.



Here is the adjacent lateral, built and fired at the same time with same technique and same parameters, but is much denser.

Al - I noticed some of your units are real nice and dense but then others have the same micro pitting also so whats the secret to getting consistency...

Phew think thats about it. Im kinda out of s now so would be great if anyone has a suggestion for improving density?

Oh yeah, and tried using a square brush instead of a round one.. didnt help (this last ones a joke, its what a rep told us to do once after consulting their expert, to solve another ceramic issue we had years back )

 

[martintay]

Paul, have a look under 10X or 20X magnification and see if crown is full of minute air bubbles !

 

[paulg100]

OK martin will check tomorrow and report back...ta

 

[Al.]

I havent been getting it lately. Im firing my first bake higher.

I dont know, I suspect it is the firing temp. At least for me.
There seems to be a real fine line for emax ceram where you get porisity or it is just right or it is over fired.
I tend to over fire the first bake for sure and it is crystal clear. No hold time.
2nd bake I drop the temp 5 degree F, if I fire it a third time I drop it another 5 degrees.
I glaze lower to keep the sharpness.

 

[user name]

Furnace to furnace numbers comparison might not be too much help, but my ceram high temp is 750 with a 1 minute hold. I cut the vacuum at heat up so the hold is in air. Doesnt look like weak vacuum. Id be guessing a little contamination in the glaze? water? Possibly from the tissue youre using? Must be no scents or lotions.

 

[REJ]

Usually it can be helped with lowering ramping, unfortunately I think I lost my prentation on this from midwinter 2009. The air must drawn out prior to the outside vitrifying or this I'd the effect. Make sure it takes long enough to reach glass transition temp on the outside so that the inside is fully dry. Dry time and ramp rate.

 

[DMC]

Rough surface texture/wrong type or too wet with de-bubblizer may cause a thin layer of weak investment? Maybe too much vibration during pouring of investment? Something to do with debris getting caught in in material during pressing? Maybe crap in yo'wax pot even?

Just a random thought. chit, I don't even press anything. What am I talking about? LOL

I use to give a hard puff into the rings before I cast them. My though was to get out any loose pieces of investment?

 

[Alistar]

I was getting this with my e.max ceram off and on too. I bumped up my first wash fire and lowered my heat rate on all dentine/enamel fires to 45c a minute.

Are you placing some units on the outside of the tray, and some on the inside?

I'm almost certain it's under fired like everyone else is saying.




Sent from my DROID RAZR using Tapatalk 2

 

[REJ]

It's in my opinion not so simple as under fired it is more like differentially fired the outside is firing first trapping air micro bubbles.

 

[desertfox384]

I get a rough firing when doing emax but almost exclusively on veneers ???? I asked Ivoclar techs about it and the only suggestion they gave me was to make sure I fired the crowns elevated on the firing peg or else raise temp a bit. Im using ep5000... you would think the temps would spot on... guess not.

 

[DMC]

This material is naturally porous? When pressing I mean.

Why have to release air bubbles with vacuum and special temp?

This is normal procedure? Sorry, I don't play with emax.

 

[REJ]

Scott it's bubbles in the veneering emax ceram, pressing is usually quite low on porosity as the pressure forces bubbles out, think of the investment as a coffee filter that keeps the ceramic trapped but let's air escape.

 

[user name]

Time to fire up a few clear tabs to dial in the perfect temp. Wouldnt hurt to give everything a once over and wipe the seal on the platform/muffle, check that vacuum lines are a snug fit. Dont cross contaminate with any component from another system. Clean water, separate tissue, e.max-only glaze brush.

Are you saying that everything looks good up to the glaze...then the pits show up? And its a natural glaze or paste? Possible youre suffering from inconsistant voltage? That can really throw off your numbers. How are you cleaning the surface between anatomy and glaze? No, No, No steam cleaner!

 

[Bumfrey]

You pointed out the main factor in what i think the problem is. You fired 2 crowns that were manufactured to exactly the same parameters, but one has these 'micro bubbles'. I am fairly sure its the placement in your furnace. Even at equal distances from the edge of the crown stand, differing areas of the muffle can make a difference. I have a definite 'hot spot' in my e700 ivoclar furnace. All my crowns fired perfectly around 300 degrees of the furnace except the last 60 degrees. (front right of muffle as you look at it). Crowns here are ALWAYS very slightly over fired. Not to a large degree but its there. I'm guessing this 'could' be an influence.
Hope that helps
Word.

 

[charles007]

Paul, do you always use the same brand of tissue ? (I think the problem is your techniques, a very slight inconsistency moisture difference in blotting, drying, dry brushing, etc.. I like to give a slight tap on the die to see a slight sheen/wetness appear, then blot and place on peg,,,, and never blot on the facial surface )
Do you give a light tap or two before blotting. Have you tried a fan brush.
I always fire porcelain/bisbakes on the high side with the slightest texture and highly glazed, drop 5 C on each additional firing like Al, glaze at 723.. 2 degrees below program on my ep 5000../p500
Just read your post again,, You said it happens more often on 2 stage firing..I bet your porcelain is dryer than your first bake when it goes on the peg, and not as dense as the first bake since you use a little condensing in some fashion. Your working the porcelain with your brush and bloting often in your single bake, and your porcelain is thicker, more wet, and condenced more. Your add on/second bake is probably done quick using a thin layers and it dries quickly, this = less dense porcelain and pits appear. (I mix Z liner liquid with my dentin/enamel porcelain for my wash bake only,, no tapping or blotting needed, and comes out very dense..)
Paul, on your next case try keeping your porcelain a little more moist as your doing the second buildup add-on and give a tap once off your model, contacts added, and still on your die. May want to try a touch of z liner liq mixed in with your modeling liq. I've never tried that ! As we all know the newer porcelains are fine grain and don't need all the condensing we grew up doing, actually can create problems sometimes using old school techniques.
Paul, we all get pits from time to time.. a pinch of dentin mixed with glaze liquid when glazing works great to hide flaws.. Polish with wheels after glazing and pits disappear..

 

[paulg100]

Wow some great help and ideas here thanks.

wont have time to post and cover all the comments until i get home tonight...

 

[Al.]

I get a rough firing when doing emax but almost exclusively on veneers ???? I asked Ivoclar techs about it and the only suggestion they gave me was to make sure I fired the crowns elevated on the firing peg or else raise temp a bit. Im using ep5000... you would think the temps would spot on... guess not.

That's exactly what I had to do !
Fire veneers separately from full crowns and fire them 10 F higher to get clarity in the porc. But I also have to fire all crowns I place directly on the tray At a higher temp. So I have a separate program for crowns on raised pegs vs crowns put directly on the honey comb tray.

For me I find if I fire emax crowns to a slightly grainy surface they will for sure have small pitts through out. If I fire to a slightly shinny surface it's clear.
I don't have that same problem with metal ceramics.

 

[bonded]

Paulg100 like other said, But i agree with charles007( try keeping your porcelain a little more moist as your doing the second buildup add-on and give a tap once off your model )
Not too moist, When i did course with Oliver Brix he mention about not to dry it a lot that cause micro porosity !!

Bye the way nice lateral

 

[charles007]

Think of porcelain like sand on the beach.. Waves wash in an totally saturate the sand, then the hot sun bakes the sand uniformly and you end up with very dense sand you can walk on. Take beach water and rewet different spots here and there, you will have large pits, and sink down in spots
I will name it the 007 Sandcastle Theory.. lol

 

[bonded]

Could be charles007 ,
Because paulg100 said he fired two crown at the same time so either one of them was too dry OR
what Bumfrey said ( the placement in your furnace. Even at equal distances from the edge of the crown stand, differing areas of the muffle can make a difference) But that very rarely happened .and whey not happened on PFM because of the high temp.