Final model pouring

[Didley]

Hi every one, I'm from Australia and have just found your great site.

I have a question regarding the pouring of final impressions for denture work. In teaching institutions over here it's taught that finals should poured and allowed to set in a position in which gravity is pushing down on the stone and into the impression. Either boxed in with wax or by a two part pour, first pouring the impression, allowing to set then a second pour to base it.

I've always inverted the filled impression onto a mound of stone. I believe the recommended method is a fool proof method for unskilled operators. Can anyone enlighten me on any science either way on this.

Sorry if my technique description is hard to follow.

 

[rkm rdt]

Rule #1

No cow pattys!

 

[Clear Precision Dental]

Rule #2
Gravity.
When you invert, gravity is pulling on they stone and the impression. It is most notible with anterior teeth, you see some thin teeth (they look like the patient has bulemia). I learned to NEVER flip an impression. There's a very fast technique to box using alginate and a magnetic boxing strip.

 

[Kreyer]

Alginate with Magnetic Strip

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[CYNOSURER]

Didley, I tend to agree with you. To many newbies mix stone too thin...how they can mix it so thin and still get air bubbles is beyond me.

The possibility that inverting the impression may cause the stone to 'drop' and create a void may be possible with a runny mix and a slooooow hand. But with a good mix any drop will simply create a slight vacuum till the 'dropping' pressure is relieved by the upward force created when placing it on the 'cow patty' and pushing down.

The other concern non-inverters worry about is the gravity induced migration of air and, even worse, water to the surface. Air causing obvious bubbles and water creating a chalky or micro bubble surface as it later evaporates. I haven't found that to be a problem. I usually invert, though I'm in no hurry to. If I'm pour up a master and an opposing I usually pour the master first the opposing second then invert the opposing first and the master last.

I haven't seen any of the problems that one would find with a porous or chalky impression when I process.

I wonder if 'box and pour' is a technique that is no longer necessary with today's materials. All my duplicate models are poured without inverting them as the flask makes inverting, not just unnecessary, but silly. That I can see no difference in the two methods doesn't mean there isn't. The real question is simply: Is there enough difference to warrant the time and trouble to box and pour?

Of course, some of the impressions I've gotten lately weren't worth the time and trouble to pour using any method.

 

[CYNOSURER]

So Rob,

Are you boxing to create land nice areas or to prevent model distortion.

Distortion from weight of the stone (especially in lower lingual extension areas) if left uninverted or distortion from the migration of stone if inverted?

I can see the benefit on some lowers...would rarely see the benefit on many uppers.

Land areas are nice but, for me, not that necessary and often annoying. They are like docks, if you're docking a big ship you may appreciate the comfort a nice big dock gives you but the reality is that the ship comes along side of the dock and not onto the dock. And if you have a little dingy like mine, then the big docks are impressively annoying. The denture doesn't extend onto the land areas. I also find land areas hamper my Ten Minute Denture Waxing Technique as it can hinder the proper angle of the brush and will have to be trimmed.

 

[Flipperlady]

I agree with Tim. I invert most of mine. I'll put down a layer of paper towels on table and plop down my bases. The paper towels soak up a little excess water if any while i'm pouring models to avoid "cow patties". This is for mostly edentulous models though. If I pour up models for frameworks then I don't invert and make a base after first stage has set up.

Michelle

 

[hydent]

here's how I do it, similar to Rob K , little different contraption but same idea with the alginate. It actually doesn't take much time at all.

 

[CYNOSURER]

Oh great, now I got an ashtray to trim....A little time here...a little money there and soon we're talking big time and big money.

All the money and time aside. Why do you do it?

 

[kcdt]

I personally am a magnetic strip box and pour kind of guy. I use alginat or a 50/50 mix of plaster and pumice.
That said, in the past I used to suspend my impressions and invert them afterwards. However, I stopped that practice after I read a study that demonstrated it didn't matter.
Tim's point about proper stone mix and pouring technique are where I'd put my efforts.
But truth is, I don't get alginates unpoured, and it's easier to box a polymeric...

 

[hydent]

Alginate with Magnetic Strip

[ View attachment 788

View attachment 789

Where do you get the magnetic strips from? I live in bfe so if you can't get them at wall mart where can you order them?

 

[Didley]

Well thanks for your replies, it seems its a common practice in the US. I worked in a university dental school for 6 years and I can see where it is beneficial in that environment, cow pads every where!
If a correct water powder ratio is used and the impression is not "flipped" to early, I can't see the advantage. If bubbles of air are migrating (floating) to the surface or you've got puddles of water on the surface of your setting stone, I'd suggest you take a good look at your technique, your mix is way to liquid. However, to my thinking, this is the purpose of the system, and as I stated, it's a foolproof method for the in experienced operator, that has been unquestioned and continued by some experienced operators.

Thanks Again

 

[hydent]

Where do you get the magnetic strips from? I live in bfe so if you can't get them at wall mart where can you order them?

Evidently no one cares to anwser my ? about the magnetic boxing strips.

 

[hydent]

Is it like a trade secret that you don't want to share or something?

 

[CYNOSURER]

you can get magnet sheets at office depot or office max. They have a sticky back for mounting paper notices to metal. I suppose you could use those. I don't know if they are using something else or not.

Meanwhile...why don't you know/learn the secret handshake so that all will be revealed?

 

[Kreyer]

Evidently no one cares to anwser my ? about the magnetic boxing strips.

I was out of the lab or would of answered sooner..

The magnetic strips in my photos were purchased from Renfert years ago..

You can also get them from a sign shop that makes magnetic signs.. Just cut them into 3 X 8 inch strips..

The main reason I box a border molded impression is to preserve the horizontal and vertical dimension of peripheral borders.. Gravity is a factor but not as much as preservation of borders.

Rob

 

[Didley]

Perhaps being in the southern hemisphere, gravity is less of an influence, Yes that is a joke

 

[rkm rdt]

I use 3 inch wide masking tape to box my impressions, and a wet ball of paper towel to fill the lingual aspect of the md.

 

[hydent]

Thx Rob

 

[Clear Precision Dental]

That

Where do you get the magnetic strips from? I live in bfe so if you can't get them at wall mart where can you order them?

I get mine from Almore International @ almore.com. Go to shoponline/lab products /magnetic boxing strips. They are $17.95 for 2. They sell a set with a base but it is just a cheap tile.

I almost always agree with Tim ('cause he's given me some real jewels),but I don't in this case. There are a multitude of errors that can occur..
Why not try to do (and teach) the very best at every step?