Polyvinyl Model Pouring help

mshiss

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File_000.jpeg Hi!
I have one dentist account that always sends me polyvinyl impressions. Not only are they missing landmarks sometimes, but no matter how I pour them, the teeth always break off in the impression if they are bulbous. I am so frustrated and want to request a different method. Most of my other accounts send models that are poured in office or alginate impressions. This account ships cases to me. I always spray the polyvinyl with model release. It doesn't matter if I use die stone or let the stone harden all damn day. Is it me and something I'm doing? I just want to make the best appliance I can for them and if I can't get this impression situation under control I may have to quit doing their work. It's not worth the headache. HELP!
 
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2thm8kr

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What stone are you using to pour them up? Is the impression material heavy body?
Don't invert the impression, probably wont help with breakage but will help with better accuracy.
On teeth that have major under cuts you can use a scalpel blade to make slits in the impression material
this provides relief for the stone as it is removed from the impression and most times is imperceivable
in the set cast.
 
TheLabGuy

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That polyvinyl (pink) one is fine, if you have undercut teeth and it's not going to hurt the appliance, slice the interproximals before pouring. The bottom one looks like polyether (gray) to me, which is much more viscous and tough. I'd suggest the same but with this one, let the stone harden up half a day, and place it in some very hot water (this will soften up the impression material) for 5 mins for an easier removal. Try to remember your draw on those anterior. If you try just removing them by the posterior, you'll break it every time. Be Gentle!!! :)
 
CatamountRob

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Tried reinforcing the teeth with pins? Stainless siding nails work great. They are small diameter and ring shanked, I cut them in half. I don't have much trouble with PVS, but PVE (Impregum) is a bear.
 
mshiss

mshiss

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What stone are you using to pour them up? Is the impression material heavy body?
Don't invert the impression, probably wont help with breakage but will help with better accuracy.
On teeth that have major under cuts you can use a scalpel blade to make slits in the impression material
this provides relief for the stone as it is removed from the impression and most times is imperceivable
in the set cast.


I am not sure of the heavy body. Most of my accounts only use alginate or accu-gel. I am not very experienced in polyvinyl impressions. I am using a Type III lab stone. Should I ask for them to use the pink polyvinyl strictly? I have noticed it being more flexible. Great idea on the hot water. Thanks
 
mshiss

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What stone are you using to pour them up? Is the impression material heavy body?
Don't invert the impression, probably wont help with breakage but will help with better accuracy.
On teeth that have major under cuts you can use a scalpel blade to make slits in the impression material
this provides relief for the stone as it is removed from the impression and most times is imperceivable
in the set cast.


Good Idea on the slits.
 
CoolHandLuke

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that yellow stone is not good. easy to bubble and foam.

suggest two things. 1. find a supplier of blue labstone or fujirock. 2. once the pour has dried let it harden in a pail of water for half an hour. open the impression underwater.

dont use a lubricant. most stone just absorbs it into the surface and you get bubbles.
 
JKraver

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This is for dentures? I don't see any preps. If they are for immediates who cares lol as long as you can get the bite from the remaining.
Edit: I didn't not realize this was in removable section when I wrote this.
 
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JMN

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View attachment 26603 Hi!
I have one dentist account that always sends me polyvinyl impressions. Not only are they missing landmarks sometimes, but no matter how I pour them, the teeth always break off in the impression if they are bulbous. I am so frustrated and want to request a different method. Most of my other accounts send models that are poured in office or alginate impressions. This account ships cases to me. I always spray the polyvinyl with model release. It doesn't matter if I use die stone or let the stone harden all damn day. Is it me and something I'm doing? I just want to make the best appliance I can for them and if I can't get this impression situation under control I may have to quit doing their work. It's not worth the headache. HELP!
Hang in there. It's a learning curve, not a learning point.

Check your stone IFU, initial setting time, and if listed total setting time. Most stones will continue to get harder and harder over about 3 days. Leaving it for 3 hours vs 45 minutes though will make wonders for how well it can take the stress.

Before trying to separate the model from the impression with any force or torque, take your labknife around the entire buccal and labial where the impressino material and tray touch or overlap. You are not going to keep all that stone when/if you make a border cuff land area. Gently press the knife into the joint and find exactly where to stop. The grey area is roughly this.

Think path of insertion. Between the purple palatal surface line's angle and the green labial surface angle is the angle of that path. Generally about where the red line is.

When removing on that path, keep the impression tray and the model on the same plane as they began relative to each other. Don't tilt the tray on the model or you will have fractures every time. Go slow. Always turn your knife so that the blade portion going into the tray is rotating towards the anterior to help that path of insertion idea. The Yellow area is what would be revealed by the tray's removal during the process, it is an even amount. Work around and around and around until it moves uniformly.

If you have a spot that wants to move fast and freely, that's a danger zone. Don't be tempted to go with it. It will cause a rotation of the tray relative to the model and will certainly break something.
20170615_103710.jpg
 
JKraver

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Spend the money get a vacuum mixer. It will make your model work better. Denser less likely to break. That stone does look like it isn't very good.
 
JKraver

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Hang in there. It's a learning curve, not a learning point.

Before trying to separate the model from the impression with any force or torque, take your labknife around the entire buccal and labial where the impressino material and tray touch or overlap. You are not going to keep all that stone when/if you make a border cuff land area. Gently press the knife into the joint and find exactly where to stop. The grey area is roughly this.

Think path of insertion. Between the purple palatal surface line's angle and the green labial surface angle is the angle of that path. Generally about where the red line is.

When removing on that path, keep the impression tray and the model on the same plane as they began relative to each other. Don't tilt the tray on the model or you will have fractures every time. Go slow. Always turn your knife so that the blade portion going into the tray is rotating towards the anterior to help that path of insertion idea. The Yellow area is what would be revealed by the tray's removal during the process, it is an even amount. Work around and around and around until it moves uniformly.

If you have a spot that wants to move fast and freely, that's a danger zone. Don't be tempted to go with it. It will cause a rotation of the tray relative to the model and will certainly break something.
View attachment 26604
That grey one doesn't seem to care about insertion angle.
 
Gru

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The obvious, but basics:
Make sure your water/ powder ratio and mixing time is correct to maximize stone properties. Manufacturers sometimes change the ratio and unless we adjust the stone will not reach correct expansion and harden to it's potential. Also, use pins and slice interproximals in likely weak preps where possible as stated above. We use extra brass pins that we roughen at need.

JMN,
I hope I'm done with this business long before we see a 27% growth in the denture market!
 
JMN

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That grey one doesn't seem to care about insertion angle.
Thats a poor drawing in Paint and grey is not the angle lines, but the breakjfree thin/loose stone before you get to solid 'real' model
 
JMN

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The obvious, but basics:
Make sure your water/ powder ratio and mixing time is correct to maximize stone properties. Manufacturers sometimes change the ratio and unless we adjust the stone will not reach correct expansion and harden to it's potential. Also, use pins and slice interproximals in likely weak preps where possible as stated above. We use extra brass pins that we roughen at need.


JMN,
I hope I'm done with this business long before we see a 27% growth in the denture market!
Just a marketing card I had handy for a window light block. IDT is having a digital denture symposium in October at Baltimore MD is what that was all about.
 
M

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I would use die stone let it harden as per instructions, soak in hot water for a few minutes then separate, this has usually worked for me. Another option if the previous one did not work is to section plastic tray and remove then remove the impression material from model by sectioning with a scalpel.
 
mshiss

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Luckily this is an immediate and I can move forward. I seriously can not wait to get another one to pour and use everyone's suggestions.
 
JMN

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Luckily this is an immediate and I can move forward. I seriously can not wait to get another one to pour and use everyone's suggestions.
If you still have that case, you can also repour the impressions and see what difference it makes with a side by side comparison.
 
Bumfrey

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Putting pins in the teeth can help.
 

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