Help with micro porosity in ceramic

[Bobby Orr ceramics]

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.

Very important point !! start entry temp at 325C so ceramic is completely sucked dry of air before initial vitrification.

 

[paulg100]

OK thanks for all the suggestions, Sorry for the slow response, got a little pre-xmas rush on at the minute and needed time to write a considered reply..
just to follow up on some of these:

"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. "

Its strange because this is the complete opposite to what Brix was teaching at idea but i think it goes to show that what works in one persons hand is not the same as another.

"Id be guessing a little contamination in the glaze? water?"

The porosity is in the ceramic, before any glaze firing. Even then ive tried with pure distilled water, pure build liquid (different types) and a mix of the two, and none seemed to have any improvement on the random porosity.

"Possibly from the tissue youre using?"

Have tried drying with tissue, and without using tissue - using warm air (hair dryer),neither made any improvement to random porosity.


"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."

Currently using Brix's parameters, including 450c dry and ramp rate of 50c for first bake and 60c for second. But will look into this suggestion.

"Rough surface texture/wrong type or too wet with de-bubblizer may cause a thin layer of weak investment?"

issues are related to emax ceram not the pressed core , all me anterior work is fully layered on the buccal

"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?"

Seems odd that the density of the first bake would case bubbles to form in the second bake layer, but second suggestion for heat rate so maybe something there.
Units are randomly placed yes. Im using an ivoclar P700 with their new muffle technology which i thought was meant to create even temperature distributing through out the chamber but maybe its not that effective, so will look into that

"make sure I fired the crowns elevated on the firing peg or else raise temp a bit."

Yep all my units including veneers are fired on ZR pins with a small blob of peg putty to tack em in place. If i HAVE to fire direct on a tray id bump a good 10c or double stack 2 honeycomb trays)

"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!"

Firing tabs to dial in exact temp is problematic as your firing on a tray which is not where you fire the crowns. prefer to fire clear onto a coping if im doing that. However P700 has very accurate auto calibration with mercury switch, which i run every 6 months. Have run vacuum check program and vacuum reading is great. Have thoroughly tested the liquid issues and have eliminated that as a factor. tissue issue eliminated as problem even without using tissue at all. The porosity is in the ceramic not the glaze, is present in ceramic after 2nd bake/enamel layer.

"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
I have a definite 'hot spot' in my e700 ivoclar furnace"

Yes i think placement /temp variable may well be the cause, will look into that. Did you mean P700 or e700? the muffle tech in the P700 i use is supposed to eliminate the hot spot issues but maybe its not THAT great after all

"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 )
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.."

Charles, yep i think your right about the thin second layer drying out more. To be clear i never condense apart from a little tap at the end like you mention. I build pretty wet on the second layer though. Re mixing in Z liner, i was adivised something similar to mix in 1/3 stain liquid, but this has not helped. re the pinch of dentine with glaze liquid, sounds like good idea but i think that will likely cause problems with the surface texture ive carefully put on before glazing. In the past when ive tried rubbing powder into the surface of the crown before painting glaze on, it create a horrible gritty surface on the glaze crown. When you polish it back to how you want it, the surface texture is ruined.

"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."

Al same here, dont seem to have the issue with Inline just emax ceram. Will check the grain thing. and see about bumping temp back up. As for different temps for veneers/crowns as above im firing all restos on pins with peg putty. using the peg putty also allows me to angle the unit so that when the ceramic goes molten, and pulls towards the biggest bulk, i can control where the incisal edge ends up, ie not flopping forward or leaning back, but right where i want it.

"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"


Yep i think i need to look at that more, thanks.

"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.. lo"

I like that theory, think i might have to nick it for a presentation some time

"and whey not happened on PFM because of the high temp."

Inline has a wider temperature band and is not as sensitive as emax ceram

"Very important point !! start entry temp at 325C so ceramic is completely sucked dry of air before initial vitrification."

Noted thanks


So! in summary ill take a further look at ramp rates/dry times, final temp , furnace placement and dry/wet state of build. I think ive already eliminated all the other possibilities. Ill have to go through all this as thoroughly and methodically as i can, which is going to take some time, but hopefully i can solve this issue and start getting to a consistent result.

It really does ruin your work when you take alot of time on creating fine details (the little scratches on the second central there are intentional) and then some micro blows ruin it. Ive also seen this issue on published work from some of the best ceramists in the world so its not a problem limited to us mere mortals. But then there are other ceramists whos work is always super dense so there must be a key here somewhere.

So back to R&D Ill post back when i get to the bottom of it.

Oh and heres some info i came across whilst researching this problem that might be of interest to you:

http://randwick.sydneyinstitute.wikispaces.net/file/view/cms+Firing+Dental+Ceramics.pdf

Needless to say ive tried changing the vacuum cut off but didnt help.

Although i have plenty of books on ceramic, none of them seems to go into the real science of firing ceramic, if anyone has a book that does then please let me know. Maybe the Yamamoto one i asked about in another thread?

and sorry about the wall of text tried to make it as readable as possible.

 

[charles007]

Paul, on my ep5000 and p500 I haven't changed the low temp.. 450 or dry times..For those that don't own a Ivoclar oven, the temp drops very low once you place in oven and push Start.. There's a setting so you can change to hold the low temp as its drying !! Did you change this setting ? I thought this was wierd the way the temp drops as its drying , but maybe helped in firing dsign porcelain and emax ceram..
Anyone with Ivoclar ovens changed this hold the low temp setting while drying ? if you did ,what changes did you see in your porcelain ?

 

[paulg100]

i havnt messed with the start temp or dry times yet either. the first thing ill do next week is probably eliminate the possibility of hot spots in the chamber as its a black and white test, and go from there.

 

[rkm rdt]

Paul I fire each bake ,usually 3 in total, on my 1st bake program.
Emax is a low fusing porcelain, so I prefer to slow cook instaed of high bake.

By the 3rd bake, I find the complete build up has matured and the colours remain stable.

Les shrinkage too!

No bubbles,no troubles.

 

[Bumfrey]

yeah it was p700. i was tired. i am always tired. Building a business from scratch and have 3 small kids. Tired and frustrated. I will stop there.

 

[paulg100]

OK! been a while but just wanted to follow this up and say thanks for everyone's suggestions.

heres the consistent results im getting now:



These are not finished yet, just two builds (+ one low temp internal stain fix),and smoothed off with rubber wheels ready for glaze firing (glaze liquid only).

If it wasnt for the few little adds that need doing to the contacts, id probably just buff these with diamond paste and not even bother with a glaze cycle.

The density im getting now is probably better than ever so it was worth the last month of pain.

Most of the problem was that i was putting me build ups in too wet, so at the end of my build im back to blotting plenty and drying out quite a bit with tissue before placing in the muffle. Yes i know on alot of courses you will be told NOT to blot with tissue, well.. i say do what works for you dont think anyone would argue with the above results.
I also changed my firing parameters quite a bit, longer dry, slower climb and higher temp.

So there you have it, hopefully no more problems until the next issue comes along

 

[user name]

That looks first class! Just a question though...why use a glaze liquid if no powder?

 

[paulg100]

Liquid will be used as a carrier for some subtle external staining.

 

[JohnWilson]

Looks awesome, love to see the surface texture after you glaze them, I bet the contours will pop compared to the rubber wheeled look now.

Very nice work!

 

[bonded]

Very nice paulg100 looks Natural !!

 

[Scotts studio]

Great job on the laterals, I use a small amount of glaze powder mixed in for my 2nd bake, seem to help me. someone mentioned no steamer ! Can I ask why not? I soft sandblast steam clean - air dry - rockin roll !

 

[Ryan Gottlieb]

I have not read all of the post on this thread, so I'm sorry if this has already been suggested.
When you do your seconded build up, do not let it dry out. This can happen very fast since it is so thin. Every time I fire thin emax ceram that has been alowed to dry out, I get this porosity.
Hope that helps.
Ryan

 

[Gav]

Not sure if this is what Ryan is talking about but these problems can occur when the porcelain on the slab, not the tooth, dries out and is rewetted.

 

[Scotts studio]

Good thought Gav, Iv'e been using the tropical trays for years, but most of the masters I see use a slab - does anybody understand why? I can't stand re-wetting my porcelain, I like to see the color of the different powders so I can mix them together by eye. I bought a MPF ceramic tray ,used it once and now it holds down paper pretty well.

 

[paulg100]

thanks guys,

I use a wet tray (smile line) so no problems with dry out on slab.

Im pretty sure i have the issue sorted out now, seems i was putting the build in to wet. Im back to drying them slightly with a tissue now and given em a quick brush over with a dusting brush and this has sorted the problems out.

Its a tough one though, if you over dry with tissue etc then this can effect the vitality.

 

[Al.]

Good thought Gav, Iv'e been using the tropical trays for years, but most of the masters I see use a slab - does anybody understand why? I can't stand re-wetting my porcelain, I like to see the color of the different powders so I can mix them together by eye. I bought a MPF ceramic tray ,used it once and now it holds down paper pretty well.

I think it is way too unproductive to use a slab.
I think you always see them using the slab because they are not showing their real production work but a single anterior with 15 different powders and mixes.

IMO it's great for show but not practical for 95% of techs ESP if you want to make money.

I have the Tropicana tray too with 19 separate compartments.
I could not imagine custom mixing several different powders for each crown except for single anteriors.
But for single anteriors I use a lot of stains on emax cores.

 

[paulg100]

i remember the Brix course i took a couple of years back at IDEA, Oliver was using a slab but im sure he said he uses a wet tray at the lab, he just didnt wanna cart it around with him.

 

[Al.]

i remember the Brix course i took a couple of years back at IDEA, Oliver was using a slab but im sure he said he uses a wet tray at the lab, he just didnt wanna cart it around with him.

That makes sense. Also putting out the powders they are explaining what they are using and why.
Mostly for teaching purposes ?
A slab or one open tray and your throwing lots of money every time you wipe it off and put out new powders
Not to mention the time of constantly remixing.

I really like those MPF wet trays but they are useless to me with one open tray and not individual compartments to put out all my body shades A-D and all my different incisals. I also have compartments I always keep Intensive White and Occ dentin orange and brown always premixed.
I never have to mix 80% of my powders. Just add to what is already there and let them get wet from underneath
plus a couple of drops of liquid and I'm working lickity split.

 

[karabear]

I use Emax-just started stacking about a month ago and wrote the pitting off as something in my technique. I just fired an 8 unit anterior bridge with the centrals in the middle of the tray. The cuspids and bi's which were near the edges of the tray were pit-free, but the lats and centrals had pitting.