Partial Dentures Created Using Selective Laser Melting (SLM) Technology

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This laboratory technical update will revolve around partial dentures. Partial dentures have changed dramatically in the past 15 years, but especially in the last couple of years with what’s called selective laser melting of how we make these partial frames. Put this kind of funny picture on here because partial frames for the modern dental laboratory are a monster. But there was a period maybe three years ago, four years ago, where at least 40% of our partials when they were cast were rejected for miscast or misfits, just errors. There was a whole generation of technicians who were great at casting, waxing, casting, investing, screwing, des, spewing, all that, and that that’s kind of an art that’s just becoming lost. They probably still teach it in the few remaining dental technology institutions, but for the most part, it’s laboratories who do their own training. And training now is digital.So when we had this problem, you can imagine if 40 out of a hundred partials were remade internally, there were also external issues too. So that was a real difficult challenge for our laboratory for the longest time for years. In fact, casting, this is what a casting looks like when it’s done. Traditionally, somebody, some technician has to go and take this case and grind off all of that surface carbon, all of the surface material, try to smooth it. I mean, just look at the inside of this clasp and underneath this rest seat and just imagine taking a burr or any kind of grinding or tool and try to make that ideal to fit that crown. I mean it’s, it’s obviously not impossible. We did it for decades, but that’s what a partial looks like when it comes out of investment. And so you compare that with what we’re doing today with S SLM technology.

It’s selective laser melting. We’ll go through a little bit of the process of how that works, but compare those two. All right, traditional with this. So this is how it comes out of the bath of lasered particles, and it’s the inside of it barely needs to be adjusted. It just needs to be smooth a little bit and polished. And there’s actually equipment that we have a very expensive, I don’t know, it’s a hundred and a hundred some thousand dollars piece of equipment that does essentially what a Val Mons machine used to do, which is it’s a vat of basically ceramic beads and the machine. I have a little video of it coming up, but the machine basically massages the metal instead of adjusting it. And so it just smooths out the surface, but doesn’t remove anything. And that what really adds to the efficiencies of, I mean, the accuracies of it. So with a typical case, we’ve been using digital technology for maybe 15 years where we digitally design all of our partials, a hundred percent of them.

Historically, what we’ve done is…Hit pause on that. Historically, what we’ve done is design the partial digitally with a software. We’ve been through about four different softwares, but they all do the same type of basic thing. And that is they survey the model. They allow you to adjust. It’s kind of, it’s computer aided design. So you rotate the partial digitally until you, I idealize the path of insertion. So instead of using a traditional nay surveyor and older technology that worked, we do it digitally. So as you manually oscillate the model, the software will tell you essentially where to stop so that the undercuts are indicated. And then you can design your partial with the both a perfect draw, perfect path of occlusion. So we did that for years, and we would print it in wax for a while, which was a challenge trying to print wax and then cast it.

And then we started printing resins. But resin, cross arch resin and resin that extends out from the pallet to the clasp and the rest seats and so forth, had a tendency to shrink and warp during the printing process. So we would cast it, and then of course the casting would come out and it would have problems, and it was a perfect digital file. And then sometimes a perfect printed file. And then the traditional casting is what messed up the process. So when they invented this S SLM technology, then it was a true digital to digital. So the file would go into a software after we designed it, go into a software, it would get nested on this platform, and then this laser would

Essentially hit the surface of this vat of chrome cobalt particles, and it would design a platform and then a partial. And so the platform would slowly sync, and so the next layer of particles get zapped by the laser, and then incrementally at the micron level, a partial gets designed or it gets built. And that is a true one-to-one. So what we design is literally what we get when we print these partials. And this is what the plate looks like right here. So all these partials are lined up on the plate. They’re all perfectly supported with these little struts underneath each part of the partial. There is no expansion, there’s no warping, there’s no heat, hot and cold elements of it that all the elements that you have with traditional casting. And then once it’s finished, it essentially goes into this machine. So this machine has eight little clasps on it, and you bolt, basically screw in a partial on these eight little, these eight little arms.

And this thing just goes around in a circle for an hour or so, and it polishes the partial until it’s just about as smooth as can be. So this is how they go in with a little bit of human adjustment on these before they go in the vat, and then when they come out, they’re just perfect. And so you can imagine that going from a 40% internal remake down to nearly zero, it’s really rare when a partial comes out of this machine and it doesn’t fit perfectly to the model. Sometimes you have to do a little bit of adjustment, but investing in this expensive technology was totally worth it to have this kind of accuracy. So for the most part, laboratories in America, if they’ve adopted this technology, they’re printing. There is, since this is a technical update, there are methods of milling frames from chrome cobalt.

So this is a plate of solid chrome cobalt that goes into a milling machine, and then just the machine uses a burr and it basically grinds out a partial denture. Historically, I mean, we’ve been involved in printing and milling for years and years and years, and the milling is usually the least efficient. There’s bur costs, you know, have to replace all the burs. These machines are very expensive, and you can only make seven or eight at a time. That’s all that’s available on the build plate. So economically, it’s not feasible to mill these out. I’m told they’re developing new mills, they’re going to be more efficient, but you’re still grinding on chrome cobalt, and there’s just a huge cost involved in doing that. Most partials that we make are still on traditional stone casts. The impressions of the cast come in, we scan them, we turn ’em into an STL file, pull ’em into the software, and then design the partial frame with a two set up.

We do both at the same time, but we have a lot of doctors, obviously with digital impressions. And if you can scan, in this case, if you can scan a pallet perfectly and you can scan a full arch with your scanner, then we can make a partial frame. We have quite a bit of experience with this at this point and very good success. One issue is the models. When we make the partial frame, we can send it out on the resin model, but when the partial comes back and we have to set teeth and then process acrylic to it, this model has to be duplicated in stone. So there’s always a little bit of an extra cost in the stone, but still you have the opportunity to use a digital impression for partial dentures. So that’s the program on partial dentures. Anybody have any questions on this technology?

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