Pouring dies & working models - Argh!

[aphistis]

We're working on a #5 gold onlay, and I'm seriously stuck. I have the prep and impressions just fine, but I'm having a doozy of a time pouring casts that aren't riddled with bubbles. I'm vacuum mixing, spraying with debubbleizer, and holding against the vibrator plate as I fill the impressions with stone. In short, I don't have any idea what I'm doing wrong, but I've done it wrong three consecutive times now, and I don't want to fall behind. Any upperclassmen want to share your tricks for getting these things right?

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[PERFECT3435]

reminds me of the time when i started trying to make night guards at work.

it took me afew times pouring cast before i got one without the stupid bubbles. i was soooo frustrated and annoyed. i finally got it. i think i was just making the cast to liquidy.



good luck Bill.

 

[anamod]

make sure the vacu-mix machine has a good vacum, a trick I learned is vibrate a layer into the impression, then invert the impression and vibrate out that layer, this should leave you with a thin film of stone on the occlusal that you can inspect for bubbles, than just vibrate the rest in. This works real well with alginate, but not as well with VPS.

 

[gryffindor]

Here are some troubleshooting pointers:

1) Do you have too much debubblizer in your impresssion? Your impression shouldn't be super wet from debubblizer, just misted over.

2) When you are using the vacuum mix, are you sure it is actually being mixed under vacuum? Make sure that the little needle in the gage flips over to the side that indicates that you are mixing under vacuum when you turn the Vac-U-Spat on.

3) Along the lines of vacuum mixing, make sure that your tubing is functioning properly. When you put your finger on the end of the tubing that attaches to the mixing bowl, do you feel that vacuum suction on your finger tip? If not, the little piece of cotton inside the tubing may need to be changed.

4) When you finally have your stone mixed under vacuum and are vibrating it in, make sure the vibrator isn't on super high. Too much vibration can cause bubbles.

5) Also, when you are vibrating the stone into the impression, use a small instrument like a #7 wax spatula to vibrate small quantities of stone into the teeth adjacent to your prep. Have the small quantities flow from the adjacent teeth into the prep while you have the impression on the vibrator plate. When your prep is filled with stone, then switch to a larger instrument (like your mixing spatula) to vibrate in larger amounts of stone into the rest of the impression.

Hope one of these solutions work. I had the same problem last year with one of my cases and learned how important #2 and 3 are at that time. Since then, I have yet to repour any of my cases senior year due to bubbles in the model when I use the vacuum mixer.

BTW, are you allowed to use a Pindex machine to put pins into your cast to make the removable dies? We are allowed to pindex as juniors and seniors and the other day I was just thinking what a lifesaver that pindex machine is when it comes time to do fixed lab work!

 

[aphistis]

Originally posted by anamod
make sure the vacu-mix machine has a good vacum, a trick I learned is vibrate a layer into the impression, then invert the impression and vibrate out that layer, this should leave you with a thin film of stone on the occlusal that you can inspect for bubbles, than just vibrate the rest in. This works real well with alginate, but not as well with VPS.

Unfortunately, we're using VPS for our impressions, but I'll give it a shot anyway. My only concern will be with working time. I don't want the stuff to harden before I have a chance to vibrate it. Thanks!

 

[aphistis]

Originally posted by griffin04
Here are some troubleshooting pointers:

1) Do you have too much debubblizer in your impresssion? Your impression shouldn't be super wet from debubblizer, just misted over.

2) When you are using the vacuum mix, are you sure it is actually being mixed under vacuum? Make sure that the little needle in the gage flips over to the side that indicates that you are mixing under vacuum when you turn the Vac-U-Spat on.

3) Along the lines of vacuum mixing, make sure that your tubing is functioning properly. When you put your finger on the end of the tubing that attaches to the mixing bowl, do you feel that vacuum suction on your finger tip? If not, the little piece of cotton inside the tubing may need to be changed.

4) When you finally have your stone mixed under vacuum and are vibrating it in, make sure the vibrator isn't on super high. Too much vibration can cause bubbles.

5) Also, when you are vibrating the stone into the impression, use a small instrument like a #7 wax spatula to vibrate small quantities of stone into the teeth adjacent to your prep. Have the small quantities flow from the adjacent teeth into the prep while you have the impression on the vibraton.

Hope one of these solutions work. I had the same problem last year with one of my cases and learned how important #2 and 3 are at that time. Since then, I have yet to repour any of my cases senior year due to bubbles in the model when I use the vacuum mixer.

BTW, are you allowed to use a Pindex machine to put pins into your cast to make the removable dies? We are allowed to pindex as juniors and seniors and the other day I was just thinking what a lifesaver that pindex machine is when it comes time to do fixed lab work!

I'm pretty sure the equipment itself is fine, since other people have poured their casts without trouble. I'll check my vacuum line to be sure, though. I'll be sure to pay attention to the amount of debubblizer I use and not to get too carried away on the vibrating. Also, we don't get to use a Pindex. We have to pour full casts and then lathe & trim them down to get our dies. C'est la vie. Thanks for the suggestions!

 

[no2thdk999]

Bill, welcome to the art part of the art and science of dentistry. This is just one of those things you learn from experience. Figure out what combination works for you and stick with it.

All of the things people mentioned above can help but you can get a void free model with no surfactant, no vibrator, and no vac-u-spat just mixing in a bowl and then tapping the tray on the table to shake it around.

I think the main thing I watch for is after you've mixed the stone, get about as much as you would use to make a peanut butter sandwhich on the lab knife and start at one end of the arch and vibrate it around slowly enough that you can watch it go into each tooth.

My only other tip that I use is set the vibrator on medium and then hold the tray such that your finger is between the tray and the vibrator. It seems to dampen it enough that it doesn't splatter the stone around. Just my style, and I've been in your shoes with my 9th pour of an impression to get a good one. Chin up, you'll be teaching your assistants how to do it before you know it.

This is one of the many things in dentistry you just have to do enough to find how it works for you.


JMHO
Rob

 

[booshwa]

Originally posted by aphistis
I don't want the stuff to harden before I have a chance to vibrate it.

i usually wait for mine to harden before i start vibrating it...much easier that way

 

[trypmo]

Originally posted by booshwa
i usually wait for mine to harden before i start vibrating it...much easier that way

Taken entirely out of context, that sounded baaaad....

 

[trypmo]

Oh, and about the TOPIC...

Needless to say, as a pre-dent I haven't done any of the stuff you're talking about, but I have done a whole lot of work with two-part silicones, and I've found the vacuum to be my best friend in the world when it comes to getting the air bubbles out of a material you pour and let harden, so I'd focus on the vacuum part.

Best of luck!

 

[UBTom]

to Bill:

Make sure you are not using so much debubblelizer that it's pooling in the impression. That will actually have the opposite effect and create bubbles (!) in your cast.

I've never had much trouble pouring up dies with PVS impressions (at least not with the Aquasil polyvinylsiloxane my school uses). The two critical points in the procedure for me seems to be:

- Mixing up Jade Stone with the prescribed 15.5ml H2O in a rubber bowl and spatula. Jade Stone is easy to mix and does not tend to form bubbles unless you REALLY disturb the mix with too much vibration or excess movement pouring it from the Vac-U-Spat after the vacuum is broken.

- Flowing only a little at a time into the depressions of the impression. Flow in too much at a time and the Jade Stone will roll over the impression with air pockets still trapped in the depressions.

Personally I've never had to use debubblelizer or the Vac-U-Spat, and my dies still come out picture-perfect 95% of the time.

My patented tip: In the rare event whenever I get a minor void, it's easily repaired with a mixture of Crazy Glue and a bit of dry Jade Stone powder, applied using a pinhead.

HTH!

 

[Midoc]

Thats an interesting idea with the crazy glue Tom, unfortunately for me I seem to be crazy glue impaired. I swear every time I try to use the stuff I get more on my fingers and hands than what I'm actually trying to glue together!

 

[booshwa]

Originally posted by trypmo
Taken entirely out of context, that sounded baaaad....

hey, at least somebody got my humor...good to see that there is some semblance of life on these boards

 

[DcS]

I'll just mirror what tom and griffen did a great job in posting. Make sure not to use too much surfactant because they can create pores on the surface. I think the biggest thing which will avoid bubbles is to pour it slowly, as tom and griffen said. The way we were taught, tilt the impression on the vibrator so the mandibular incisors are sitting on the vibrator or over your finger on the vibrator. The posterior portions will be up in the air. Take little increments of stone and pour it in from the most posterior tooth and let it vibrate down into the impressions of each tooth. Watch as the stone slowly poors into the impressions of each tooth. Make sure to do this carefully and keep adding small increments until all of the teeth are filled (you will have to eventually flatten it out to get the post). Then just add big amounts to get the base. Patience is the key, this should do the trick. Hang in there, like everything in dental school, it's a learned skill with a varying learning curve and once you get the hang of it you will wonder how you ever had trouble.

Good luck with it

You guys have to trim the dies yet? That's quite possibly the most annoying process to me (except for setting teeth in dentures...argghh). If you are trimming a die and you nick the margin, we have to start from square 1 and retake the impression and pour the stone, place dowel pins, cut dies and trim etc. Not as fun the 2nd time around.

 

[JesseBrad3]

Another thing that might help is to run water over the impression and shake out as much as you can before you pour the stone. Sometimes bubbles hide in the little crevases, but giving it a good shake usually gets them out. Like DcS and others said, pour slowly from the posterior to the anterior so that the mix gently spills over from well to well. I'm sure it'll all work out for you.

 

[DcS]

JB i sent you a long overdue PM

 

[DcS]

JB i sent you a long overdue PM

 

[DcS]

JB i sent you a long overdue PM

 

[gryffindor]

Originally posted by DcS
You guys have to trim the dies yet? That's quite possibly the most annoying process to me (except for setting teeth in dentures...argghh). If you are trimming a die and you nick the margin, we have to start from square 1 and retake the impression and pour the stone, place dowel pins, cut dies and trim etc. Not as fun the 2nd time around.

Don't nick the margin. I know it's easier said than done. Are you using PVS impressions? Like Tom said, the Aquasil PVS is what we've been using all 4 years and it can usually withstand a few pour ups before it starts looking really tattered. Unless your school has a standard way of ditching dies and won't accept any other methods, ask your clinical faculty if they have any pointers in ditching dies. It's hard to explain how to ditch them without being able to show you. My dies looked ugly (I was trimming them to look like an "island in the sea" - the way described in our lectures) until a faculty member showed me to trim the die so the base of the die ends right up at the margin of your prep.

I completely agree about the frustration in setting denture teeth.

Bill, it just takes some time till you figure out what works for you. I won't pour green stone without using the Vac-U-Spat to mix it first. Other classmates swear the Vac-U-Spat is crap and makes no difference and prefer to just hand mix the stone and vibrate it in. Some people pick it up quicker, but it took me three years to get it right and not mess up so much when pouring up impressions for fixed.

 

[aphistis]

Update: After two disastrous days trying to pour dies last week, today everything came off like a champ. I poured five dies in three hours (this is approaching world-record speed in my dental universe), and they were all 100% bubble-free. Mangling one of them on a lathe didn't help, but all things considered today definitely ended up in black ink.

I don't feel like I did anything dramatically different, but I was careful with the debubblizer and made sure to let the stone vibrate into the impression rather and not let it pour directly in. I guess the third day is the charm, eh? Thanks to everyone for all the helpful suggestions.

 

[trypmo]

 

[PERFECT3435]

congrats Bill.


now, this may be a dumb questions, but do you have to constatntly buy lab supplies (ie gloves, stone, impression material etc etc) or does the lab fees that you pay cover all that stuff throughout the semester?