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Dental lab tests printing teeth, lost wax investing/burnout/gold casting and lithium disilicate glass pressing

Mark Strohbehn
posted this on August 06, 2013 10:12 PM

Hi Form fans,

 

I own and operate a small dental lab and purchased the Form 1 printer with hopes of printing CAD-designed dental restorations for lost wax casting of metal, and lithium disilicate (Emax) glass pressing processes.  Today I made a few prints of dental prosthetic restorations, invested one of them, burned it out and pressed it in lithium disilicate (Emax by Ivoclar) using a specialized glass-pressing oven.  It worked!

 

Here are the specifics:

- Printed several crowns (teeth) on a small corner of the platform.

- .05 mm Grey material setting  (Decent surface texture when completed).

- One hour total print time.

- Cleaned the teeth in alcohol and light cured them using a Dentsply "Triad 2000" curing unit (5 minutes).

- Checked the crown fit to the master die and sealed the margin using margin wax to achieve a perfect fit.

- Invested one crown using Microstar HS Investment.  14 minute bench set time, then straight into an oven preheated to 1562 degrees F.

- 1 hour burnout.

- Pressed 1 Emax (lithium disilicate) ingot in a Zubler 300e pressing furnace.

- Sand blasted the tooth out of the investment after 30 minutes cooling time.

- Cheered loudly!

 

Check out the results.  I'm very encouraged by this first test.  My normal investing, burnout, pressing procedure seemed to work perfectly.  This process is picky about ash residue left in the investment during burnout as it leaves dark speckles in the glass.  There doesn't appear to be any discoloration of the glass. I use this same investment for my metal castings, so there should be no problems there.  There was a lot of dark smoke as the resin ignited and burned and hopefully this will not contaminate my oven over time.  There was no residue left on the floor of the oven after burnout.

The big question is dimensional accuracy.  The crowns seemed to fit the dies similarly to others I've had printed on expensive 3D printers.  They need to be waxed at the margins for perfect fit, but that is acceptable for now.  Hopefully the accuracy will improve as the Form software/hardware improves.

 

 

Comments

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Jesse Taylor

Impressive : )

August 06, 2013 11:38 PM
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Jesse Taylor

Just wondering...is your more expensive machine an envisionTEC per chance?

August 06, 2013 11:39 PM
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Douw Grobler

Mark, I am also planning to use my Form1 in my dental Lab. I will only get mine in later in the year since I am in the FORM ABROAD group. Thanks for posting your results, it gives me some hope.

 

August 07, 2013 08:42 AM
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Mark Strohbehn

Jesse, in the past I've sent my digital CAD files to a dental milling/printing center for production.  I don't know what 3D printers they use, but your envisionTEC guess is probably accurate.  Their material is an opaque orange wax/resin and is excellent for seeing contours.

 

Douw, it's good to see other prospective dental lab users for the Form 1.  After reading all of the jewelry lost wax casting threads on this forum I was a bit discouraged before my test, but am much more hopeful now that it could be a very productive tool in the lab.  What I really want is a wax-based, dimensionally stable resin with good color properties for seeing contours.  That's asking a lot.   Hopefully the clear resin will work acceptably until new resins are available.

August 07, 2013 10:36 AM
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Mark Strohbehn

Here's a lost wax casting test of a Form 1, clear resin print.  This time I tried casting a gold crown (45% gold, 6% palladium, 39.5% silver) from a Form 1 print of a CAD tooth.  Investing protocol and procedures were the same as my original post, except for using a lower burnout temp of 1152 degrees F, and casting with a gold alloy instead of pressing with lithium disilicate glass. 

 

The results were as good as when I use wax to build a crown.  There does not appear to be any problem with clean burnout of the clear resin using Microstar HS investment at the two temps I've tested so far.  Surface texture of the casting is good, but the surface of the printed crown is a bit rough (printed at .05mm).  Because there is finishing of the metal involved anyway, this isn't really a big problem.  Any areas of the print that are too rough can be very quickly  smotthed with a thin coating of wax.

 

Please keep in mind that the resin produces a lot of black smoke during burnout and a vent hood is necessary so you don't breathe the fumes. 

 

Hopefully this is helpful information.

August 10, 2013 10:05 AM
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Douw Grobler

Thanks Mark, I agree that it would be best to have a wax-based resin like the red one from B9. The clear does make it difficult to see detail but for now it is very good to know that we would be able to use the resin that come with the Form1 for dental castings and pressings. How did the fitting surfaces of the crowns come out, can you see the print layers after sandblasting? Was there any porosity present in your gold crown after polishing?

August 11, 2013 01:36 PM
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Douw Grobler

Mark, what do you use for your scanning and CAD? I'm using 3Shape.

August 11, 2013 04:54 PM
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Mark Strohbehn

Douw,  zoom in on the photos I posted and you will see some slight layering evident on the occlusal surface.  It's minimal and will easily polish out.  I will spend a minute or two flowing a thin layer of wax on rough areas prior to investing to improve surface smoothness. There were no porosity issues in the casting.  The crowns I chose to print were difficult test pieces because the margins were thin and irregular.  The fits straight out of the alcohol bath were not great, but I wasn't super careful with the cleanup procedure.  By rewaxing the margin to the die you will be able to acheive a perfect fit.  You mentioned the B9 red resin.... I'd love to give that a try and may order some to test.

 

The scans I used are from an Origin Intelligence (white light) scanner with Exocad that I used for awhile but no longer own.  I will likely buy a Medit Identica SE scanner with Exocad in the near future unless a better option comes along.

August 11, 2013 06:32 PM
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Derek L

hii.. what kind of sandblaster do you use to remove the investment?  do you use special type of sand grains?

August 19, 2013 11:56 AM
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Dave Stitt

Curious to know if you have printed any full arch models and the time/accuracy outcome. I'm looking at the form1 for a small lab that receives almost all cases in a digital format.

August 19, 2013 12:59 PM
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Douw Grobler

Mark,  unfortunately I am not familiar with the scanners or software that you mentioned, I am sure it also gives good results. Do you think the marginal integrity would be better if the margins are thicker, say a minimum of 0.4 mm? have you done any other cases with your printer?

 

Mark, I took the liberty and answered some questions, hope you don't mind. 

 

Derek, I use 50 micron glass-beads at 3.5 bar to remove the investment. Then 100 micron aluminium oxide at 2 bar to remove the reaction layer on the surface of the crown. The sandblaster I use is a Renfert Basic quatro IS, http://www.renfert.com/24185/Fineblastingunits/BasicquattroIS/20673/catalog.aspx

 

Dave, you can find dental models in this post https://formlabs.zendesk.com/entries/25241023-Thanks-to-John-Sterbonic-of-Santa-Maria-CA-I-have-some-excellent-prints-to-demo- It doesn't look promising but they had a problem with their printer, hopefully it would come out better. What software do you use and from which oral scanners do you get data. I would like to get scan data from Cerec dentist but there is so much red tape/ license fees to get the correct format for my 3shape and most of the time the sales people do not know how it works. Any help or advice would be much appreciated

 

 

August 19, 2013 03:19 PM
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Mark Strohbehn

Derek, here's the sand blaster I use: http://www.sterngold.com/Sterngold/equipment/product.aspx?pId=2102246.  And as Douw mentioned, 50 micron glass beads are used to remove investment from the casting/pressing.

 

Dave, I haven't tried printing any full arch models because I do all modelwork using stone in traditional impressions.  I'd bet it could work for single-unit cases, but I'd be skeptical about any bridge work or implant cases.  Until Formlabs makes a good colored resin it wouldn't make sense either.  When I get another scanner I'll have more flexibility to test full arch printing.

 

Douw, I think you're correct that a thicker margin would print more reliably.  I printed several veneers with cervical margins that were very thin and nothing less than about .3mm (300 microns) thick printed, which is exactly what the Formlabs specs indicate.  Since I'll be waxing the margins anyway this may still be acceptable.  I haven't done any other cases with the printer. Until I get another scanner, I'm stuck for awhile.

August 19, 2013 10:53 PM
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Jens Neubarth
Hi, I also have a small dental Lab in Germany and I will try later on in october the Same as you did with the Form One. Your results are very impressiv. I Hope to get the Same Print and Casting results as you. I will use both, 3 Shape and exocad, Systems. We may Stay in Contact!
August 21, 2013 03:14 PM
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Mark Strohbehn

Hi Jens, glad to have another dental lab tech around to help test out the Form 1!  I'll be watching for more dental lab-related posts from your guys in the coming months.  Hopefully I'll get my new scanner soon so I can start printing and posting more results.

August 24, 2013 09:11 PM
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Michael Braian

Yes 

 

This is great stuff I love to see technicians embracing this great technology. Im a dentist and a dental technician, currently I have a private practice and a dental laboratory i Sweden. I´m also a phD student at one of the faculties here in Sweden, I´m currently doing research on additive manufacturing methods. Stereolithography seems to bee one of the methods in my research that has the capability to change our line of work. Mr Charls Hull (inventor of STL) and 3D systems has been protecting their patent sins the 80ties, so I was really amazed when Formlabs announced the printer. My current research is on the Objet (30 and Eden) and printjet systems, the machines are amazing and really expensive. So yesterday I decided to by the Form 1, when I receive it I´m going to test it  and compare the data. I promise to let you know how it goes, ohhhh I might be abel to help you guys with some dental related cad problems in the future. :) 

September 19, 2013 05:57 PM
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Douw Grobler

Michael, I would like to import Cerec files into my 3Shape. Can you maybe tell my what I need and if it can be done successfully? 

 

Has anyone tried to burnout the Grey resin? 

October 07, 2013 04:09 PM
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Michael Braian

Ok so there is no easy or cheap way to do this, to my knowledge. I know that Patmo141 made a blender plugin that might be helpful it´s on youtube [YOUTUBE]a8cT0oy1XWQ[/YOUTUBE] 

 

Cross manager should be abel to do it but I have not tried this software

 

The whole Cerec, 3shape,DCM etc thing is quite difficult to convert without paying for expensive software or dongle licences.  

October 07, 2013 05:42 PM
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Douw Grobler

Thanks Michael, do you think it would be worth the effort to try and get the Cerec files into 3Shape, would I be able to use it for good quality restorations. I will look into the blender software. The dongle licences are very expensive, about $10 000( in South Africa) to do models, crowns and STL’s.

 

I've downloaded Cross Manager and will give it a try as soon as I can get my hands on some Cerec data

October 09, 2013 12:05 AM
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Mark Strohbehn

After more testing, it turns out that the Form1 resin does NOT burn out completely, as people in other threads have already mentioned.  I think my early success with casting and pressing using  the Form1 resin was luck, based on having a large pattern with no intricate lobes (like prongs and settings on a ring) and oriented in such a way that the residue ash fell out of the investment through the sprue prior to casting. 

 

I'm going to keep trying to use the Form1 resin for casting and pressing dental crowns, but there will likely be a significant failure rate due to ash residue remaining in the invested pattern.  We definitely need an ash-free resin!

 

November 12, 2013 05:04 PM