Cast frame partials not fitting.

[Coleson]

Hello all, thanks for taking the time to read. My lab is currently experiencing issues with cast frame rpd's not fitting at final stage and is obviously making doctors and patients very upset. They fit just fine at frame try-in and aesthetic try-in but after they are processed and finalized they don't fit the models or patients. My first inclination is packing them in too much pressure with a press? I would love it if anyone else has gone through this and has some ideas as to what the issue may. Thanks for any suggestions.

 

[denturist-student]

If they are fitting at try in and at fully waxed try in then something is going awry with your processing. Or perhaps the dentist is being forthcoming with you.....like that ever happens..... I do my fully waxed try in with the framework try in at the same time. Make sure your tissue stops are fully engaged at the processing....Also ensure that no thin film of acrylic is covering the abutment surfaces of the guide plates....that can be difficult to spot....I am sure that a large number of things to check during processing is needed and especially taking care when breaking it out....Partials are easy to bend....I have seen very few lingual plates that did not rock to a certain extent....Most of my problems were solved when I started dong the final impressions with a good die stone. Personally I like to use fuji rock and follow the instructions regarding water powder ratio very well and use a vaccuspat to ensure that dimensional stability is optimized even when you are doing your final impressions...hope these few suggestions help....keep well and take care.

 

[2000markpeters]

Maybe you are warping frame during devesting stage with plaster snips.

 

[JMN]

are you using a duplicate and able to verify seating on a model prior to delivery?

Can you see if there is any stress fractures in the plaster around the covered clasps and frame edges after processing? Any loose plaster bits in your acrylic? This would tell you the metal was being greatly forced during closure.

How long is the period between design model fabrication and delivery? Shift happens.

 

[Coleson]

We actually duplicate and process on that to fit the rpd to the master model at finish. At finish and quality control we are usually good at catching whether or not all rests, clasps, etc. are clear of acrylic. The reason I was thinking it might be at packing is because we got a new press machine in the lab and the problems seemed to be accruing around then. How much pressure should normally be applied to a cast frame at the packing stage? I also was thinking it could be our duplicates are way off from the original models but the frame normally fits fine on both models before processing. Thanks for all the replies everyone!

 

[Coleson]

Also in response to the delivery question JMN, our deliveries are random. Some get delivered locally by drivers the same day while some are delivered by shipment which is about 2 to 3 days. This complaint is unfortunately consistent from either methods of delivery so I would rule that out.

 

[CoolHandLuke]

if the frame fits, but not once teeth are set, you are processing wrong.

simple as that.

go back and figure out at what point the fit becomes off. i'll bet its where the frame and the acrylic are met. what is cold cure you might be packing in an oven. or what needs an oven you might be leaving out too long.

 

[JMN]

Also in response to the delivery question JMN, our deliveries are random. Some get delivered locally by drivers the same day while some are delivered by shipment which is about 2 to 3 days. This complaint is unfortunately consistent from either methods of delivery so I would rule that out.

Where I was headed was the teeth shift over time if not retained by some device. If this is only happening with one office, their protocol may allow enough time that the teeth shift between when the impression for the definitive model is impressed and the time that the prosthetic is delivered.

If it fits the models, after processing acrylic, it should fit the mouth - if the mouth and models are no longer the same, it won't.

Is it with only one office?

If it's with all offices:
are you putting them in the press too long after the acrylic is mixed? It will have less give.
Does your press go over sufficiently more of the flash than the knockout disc? If not, the disc may be receiving and applying unintended pressure.
Some of the cheaper made presses do not prevent the screwshaft from contacting the flask before the press paddle, causing issues.

You mention a new machine/process, can you do a few with the old one and take special attention to the differences and what may have changed in how things are accomplished differently?

If your old setup doesn't give errors, there's yer clue.

 

[kcdt]

Maybe you are warping frame during devesting stage with plaster snips.

This is your most likely culprit in the processing chain

 

[Bumfrey]

If you process on dups i would be a little wary. Id process on master myself. All other comments are probably just as if not more valid. I just cringed when you said it though.
For your problem i would.
Process on master after checking the fit on master AND dup.
Be more careful devesting jobs.
Id poor or inject as its more accurate.

 

[nunomrts]

Try to frame them upside down and without the model. They will end up exactly equal to the wax up.

Enviado do meu ALE-L21 através de Tapatalk

 

[MasterCeramist]

If after processing it doesn't fit master model I would remove teeth and acrylic and see how the frame fits to the master model then you would at least know if it's a framework issue or acrylic issue.

 

[kcdt]

If you process on dups i would be a little wary. Id process on master myself. All other comments are probably just as if not more valid. I just cringed when you said it though.
For your problem i would.
Process on master after checking the fit on master AND dup.
Be more careful devesting jobs.
Id poor or inject as its more accurate.

You make a valid point in terms of trouble shooting; but the wisdom of processing on the dupe depends on the dupe.
If the frame seats accurately on both, then I'd rule it out as the problem.

 

[kcdt]

Where I was headed was the teeth shift over time if not retained by some device. If this is only happening with one office, their protocol may allow enough time that the teeth shift between when the impression for the definitive model is impressed and the time that the prosthetic is delivered.

If it fits the models, after processing acrylic, it should fit the mouth - if the mouth and models are no longer the same, it won't.

Is it with only one office?

If it's with all offices:
are you putting them in the press too long after the acrylic is mixed? It will have less give.
Does your press go over sufficiently more of the flash than the knockout disc? If not, the disc may be receiving and applying unintended pressure.
Some of the cheaper made presses do not prevent the screwshaft from contacting the flask before the press paddle, causing issues.

You mention a new machine/process, can you do a few with the old one and take special attention to the differences and what may have changed in how things are accomplished differently?

If your old setup doesn't give errors, there's yer clue.

I too find it odd that the problems started with new equipment entering the mix.
It is possible to overload a frame in a press.

 

[kcdt]

Try to frame them upside down and without the model. They will end up exactly equal to the wax up.

Enviado do meu ALE-L21 através de Tapatalk

Only issue that I have with this is it places the accuracy of the intaglio directly on the adaptation of the waxup, and I suspect insuring that a layer that achieves this under the retention saddles may easily wind up keeping the frame from fully seating.

 

[JohnWilson]

Doc, here are the knowns as you state them

1) you dup your master model, "How" what material, are you using same stone for both master and dup?I know a lot of people that use buff stone for dups, I don't

2) Compression packing, nothing wrong with this at all. if you are covering the frame on the first pour with plaster you can not warp it on processing very easily. I don't care what new press you have.

3) Divesting, yeah you can bend frames here if you are SUPER carless but you have to be exceedingly carless to make this happen. Plaster snips when used correctly and you are smart enough to divest with the force away from the frame you will be just fine. Pneumatic is a different story for sure and has a higher learning curve and a higher chance of failure.

4) tooth born cases, super easy to know if you waxed up correctly as you will see your rest seats are either seated or not.

5) free end with tissue stops much harder. When you boil out the flask, look at your frame and see if its in contact on the stop when its boiled out. if it is you should be just fine. If its up yeah you could potentially be off but again really really hard to warp a frame here.

If I was a betting man I bet your duplicates are not super accurate. If you are having great fits with a try in wax up but fits like crap after you process and you are processing on a dupe, what is that telling you.

Last thing, experience fitting appliances back to duplicates for partials is not just grind and go, a tech has to be able to look at the model see the issue areas and have experience to know when the tissue will give/flex and when its rigid bone. Adjusting the acrylic in these situations is an art form and based on YEARS of service and constant communication with clients. Scrapping a tissue undercut is not something I advocate but I do do it on certain case, I am much more likely to process on a slightly relieved "blocked out" dup model that will allow me not to have to touch the intaglio.

The reason most partials have issues with fit is like most removable appliances the borders are exceedingly over extended and muscle trim/ relieve is not accomplished

Thats my 30 years of knowledge in a few blanket statements, trying not to preach here, just share

 

[denturist-student]

I always place a double thickness layer of relief wax over the gingival tissues. I have had a few patients whose appliance doesn't fit on insertion because the gingival tissues were inflamed and a bit swollen....Another thing to consider might be the time between framework tryin and processing. Teeth can drift a bit without support....Try and limit your time to less than three weeks from start to finish....and again use a good diestone....vacuspated for the models.

 

[JKraver]

What kind of press? If its a big boy unless you are the hulk I wouldn't worry about too much pressure. A push button machine clamps down with 3000lbs? That could cause issue if your stone isn't strong enough to withstand the pressure. I think most likely a dupe model issue, or divesting errors.

 

[kcdt]

Doc, here are the knowns as you state them

1) you dup your master model, "How" what material, are you using same stone for both master and dup?I know a lot of people that use buff stone for dups, I don't

2) Compression packing, nothing wrong with this at all. if you are covering the frame on the first pour with plaster you can not warp it on processing very easily. I don't care what new press you have.

3) Divesting, yeah you can bend frames here if you are SUPER carless but you have to be exceedingly carless to make this happen. Plaster snips when used correctly and you are smart enough to divest with the force away from the frame you will be just fine. Pneumatic is a different story for sure and has a higher learning curve and a higher chance of failure.

4) tooth born cases, super easy to know if you waxed up correctly as you will see your rest seats are either seated or not.

5) free end with tissue stops much harder. When you boil out the flask, look at your frame and see if its in contact on the stop when its boiled out. if it is you should be just fine. If its up yeah you could potentially be off but again really really hard to warp a frame here.

If I was a betting man I bet your duplicates are not super accurate. If you are having great fits with a try in wax up but fits like crap after you process and you are processing on a dupe, what is that telling you.

Last thing, experience fitting appliances back to duplicates for partials is not just grind and go, a tech has to be able to look at the model see the issue areas and have experience to know when the tissue will give/flex and when its rigid bone. Adjusting the acrylic in these situations is an art form and based on YEARS of service and constant communication with clients. Scrapping a tissue undercut is not something I advocate but I do do it on certain case, I am much more likely to process on a slightly relieved "blocked out" dup model that will allow me not to have to touchtone intaglio.

The reason most partials have issues with fit is like most removable appliances the borders are exceedingly over extended and muscle trim/ relieve is not accomplished

Thats my 30 years of knowledge in a few blanket statements, trying not to preach here, just share

#5 was what I was thinking about press overload.
If you perform a altered cast, it's advisable to salt and pepper a button of autocure to regain the lost contact. A unsupported freeend saddle can definitely get sprung.

 

[denturist-student]

Why don't you send a few cases out for ivocap or ivobase processing to see if the situation changes....If so then stop press packing....