Shooting acrylic

[RetainerDesigner]

How do you guys shoot acrylic on your lower appliances?
Do you do it in three parts: Right side, Left side, middle (that order?)
Do you do it in 2 parts: Right half, then Left half?

I have been still having random shrinkage of the acrylic away from the posterior teeth 6's and 7's. I have changed my pour up method (per labdude) which did lessen the instances of shrinkage.
I mentioned this to one of my doctors and he asked if I was pouring in 3 stages or not. and I couldn't answer him, i didn't know. He thinks that is why you pour up in 3 stages to eliminate lingual shrinkage..
I paid attention the next time I poured up and it looks like I was pouring in halves, I guess as a result of me trying speeding up the acrylic process and/or pouring up in patterns. I have been consciously pouring up in three stages since then like I was taught in lab school and it looks like it solved the problem. What do you guys think?

 

[labdude]

Time is a problem here, for the answer. LInda says for me to tape the procees I use for everything, then post the movie.
Will do...in time.
For now, to answer the question on what I do. Not that it is written in stone as the only way.
Upper or lower.
Being right handed, reverse for left handed.
I start at the most posterior point on the part that is closest to me. Say it's a lower, I start at the LR 6.5. 6.5 as I always start beyond where the appliance will be finished to. In this case, finished to the 6.
I will lay powder first, 6.5 to the 4, at most. Sometimes less. I consentrate on the acrylic on the gingival and tooth surface mostly. The areas down on the tissue almost are always filled corectly. Unusual shape of the structure of the bone on some requires more attention. On the average case, no.
Then I work forward to the 3 or 2, not more. Then I go to the let 3, at most.(remember this is a lower I'm describing)
Then form that left 3 to maybe half of the left 6. Then a final to do to the left 6.5 area.
Uppers are then same/ I start at the Ul 6.5. And do it exactly the same. It only varies due to bone shape. Some almost have a shelf reaching to the gingival, takes more time and I cover less ground at a time.
I do this and set the first aside. I do a second, set it aside. Then a third. Then on the pot.
Before I set a case aside, I cover it with a layer of clear powder to prevent slumping. Also, slumping is not a problem if you lay on the correct amount of acrylic.
To thick, you may experience the problem of distortion you are describing. To thin, well, is just to thin. You will have to fix that with a build up. Repair the thin if you catch it, before you remove it from the model.
I hate to bring it up, but, the only time I got a complaint about the shrinkage is when I was just crusing along for a few months, and missed the fact that I was making them to thick. Easy to do as you get faster. You can only go so fast. To fast is just as bad as to slow. It's like pumicing, it takes what it takes, time wise, to achieve a good result. Pumice is to coarse you get scratches, to fine takes to long.
Sorry, I know my posts are sometimes long, but, It ain't really simple.

 

[RetainerDesigner]

I agree with Linda about the movie. I plan on doing that more when I get a chance.

I see what your saying you start with the LR6 and work counter-clockwise to the other 6. I think I am real sporadic with the thickness too, that might be the culprit. Im gonna try that counter-clockwise method next ive never done it that way before.
The upper I just shoot half of the model then turn the model around and shoot the other side, I just have to make sure to to fill in the seam.

I absolutely despise the lowers where all the posterior teeth lean in (lingual)!
Undercut city!

Also lower Tori! They always cause weak (thin spots) in the acrylic if im not careful.

 

[labdude]

Undercuts can get ugly. I know what you mean.
In those Tori cases, extreme or not. I always have wire overlap. Even on a modle with no tori.
On a lower, it's usually the rest I extend. It goes anterior all the way under the labial bow by about 3 or 4 mm. Sometimes I do it with the clasp involved. Makes a lower a little stronger. Done carfully it doesn't increase thickness of acrylic. It also gives you a depth guide for lay on acrylic.
On uppere I don't have such overlap of wires. I do loop the ends of all wires that are in acrylic. They need that, or at least a few zig zag bends. Wires will twist in acrylic and work loose otherwise.
If you place acrylic starting on one side of an upper, and work to the other side, rather than doing halves. Your acrylic might come out less thick and require less grinding time.
I find it's not so much the use of extra acrylic that causes a cost problem, it's having to spend extra time grinding excessive acrylic thickness.
Linda will have to record me working, still, time is the issue. I wish I could do it right now, it just might help a lot of younger labs. Movies of everything, from a ball clasp to a crozat.

 

[trisha]

I usually do the acrylic in 2 steps, depending on the anatomy of the lower arch. Some times I do it in 3 steps, post.R, then post. L, then anterior section. I have noticed that if I do make the lower too thick when I go to hone it down with an egg burr i& pumice it can make the acrylic pull away slightly from the model. So I have made adj. in my acrylicing to avoid putting on too much acrylic to begin with. I hate to admit this but, when I first started, I used to put the monomer on 1st then the polymer and not the other way around. I later realized the importance of using polymer 1st on the model. Crazy little tricks I have missed out on not working in a large ortho lab.
t

 

[RetainerDesigner]

I used to put the monomer on 1st then the polymer and not the other way around. I later realized the importance of using polymer 1st on the model.

I have heard to do it both ways never have realy found a good reason. Do you soak you models completly or do a wash before seperator, like Labdue?

I have noticed that if I do make the lower too thick when I go to hone it down with an egg burr i& pumice it can make the acrylic pull away slightly from the model.

I was thinking this was the cause too for a while , like when I used the acrylic knock down wheel for bulk trim, that the acrylic was getting too hot and distorting. I guess with the combination of this acrylic this i might not be good. Looks like thick acrylic is the culprit, I have been monitoring that the pas couple of days and no shrinkage.

Cade

 

[RetainerDesigner]

Undercuts can get ugly. I know what you mean.
In those Tori cases, extreme or not. I always have wire overlap. Even on a modle with no tori.

An Orthodontist and I were talking about this, wants me to try both ways. Either wire overlap or very short wires in the acrylic. He feels that if it the wire is in the acrylic is long but with not over lap it makes the acrylic break where there is no overlap. Mainly because the acrylic cant flex where there is a wire and can flex where there isn't, so they break every time at the junction of flexability and non-flexibility. Kinda like all the flexing force is concentrated at that one point.

He wants me to try making the "tags" (the embedded part of the wire) short so that the flexibility is distributed over the whole retainer. Kinda straight down with a little bend for retention.

Should make quick work of bending wires

 

[labdude]

When I mention overlap, I don't mean on top of. More like stacked, so there is no increase in acrylic thickness. Like this=, not like this+. Clear??? as mud?
Nice theory on fracture strength. A patient who is rough on an appliance, is rough on an appliance.
I have so little breakage and repair work, it is about 0.00001 percent. Probably less. Wires and acrylic.
Wire does re-enforce the acrylic. Maybe makes it stiffer, still it bends also with the acrylic. Seems a fracture at least stays together if it has wire in it. A lot of breakage happening requires a look at acrylic thickness, undercut block outs. Also a good look at what type (maker) of acrylic you use, or combination of liquid and powder.
My lack of breakage comes form a lot of time spent on various acrylic monomer and polymer combinations. Also the way it handles when layed on the model, how fast it cures etc.
I use Hygenic repair resin liquid in all polymers. I use only JBC colors. They grind in the colors. And for clear I use GL Super fine polymer.

 

[trisha]

I have heard to do it both ways never have realy found a good reason. Do you soak you models completly or do a wash before seperator, like Labdue?

If I put the liquid on the model first and then add the polymer the liquid jumps to where the polymer is and can pull away from the model (and wires) causing a whitish color around the wires where the liquid pulled away towards the powder. It is not a clean or professional look and probably compromises the integrity of the wires imbedding in acrylic.
I do not soak models. I use seperator that I get from GL that is a thin clear liquid. I like it alot better then the pink jelly stuff.

Looks like thick acrylic is the culprit, I have been monitoring that the pas couple of days and no shrinkage

If I spend too much time on one area it can warp the acrylic, so I am constantly moving my burr around the acrylic in different spots, so as not to get the acrylic too heated.

Nice theory on fracture strength. A patient who is rough on an appliance, is rough on an appliance

Amen.

 

[labdude]

I do wax out of undercuts. Then a quick rinse under the faucet.
Next comes the separator. I use the Masel blue stuff. Get it from OSE. I brush it on and blot of excess with a tissue. Excess is generally on the wax, and won't go away otherwise.
By the time they are all painted, The first ones have no visible moisture anywhere. Then I glue on wires.
Very true Trisha, any droplet anywhere and it will soak right into the polymer, making for a real fun time to fix. Or just plain make over.
I never soak models.
Just enough moisture to keep the separator alive fro an hour or so while I lay up acrylic.
Now/....if you like totally dry way....use separator from JBC. It is silicone based and must be put on a dry model. 2 coats. It will last for week without being touched, and still function as a separator. Neat stuff, I used it for a while. I just like the damp method, simpler.