Innovation is rampant in orthodontics—to the point that we’re seeing innovation within innovation. Take 3D printing, for example. The 3D printer alone—just the printer itself—has been revolutionary. It has allowed the orthodontic practice to take control and fabricate aligners in-office, on their own schedule. But it wasn’t the 3D printer alone that facilitated this. Along the way, additional innovations were needed—chief among them the thermoforming plastic material. And now, these materials are further evolving with a new material that allows for direct 3D-printed aligners. 

Orthodontic Products Chief Editor Alison Werner spoke to Ki Beom Kim, DDS, PhD, the Dr Lysle Johnston Endowed Chair in Orthodontics, and the program director in the orthodontic department at the Center for Advanced Dental Education at Saint Louis University, on a recent podcast episode about a new material that allows for direct 3D-printed aligners.

Dr Ki Beom Kim

Kim and his colleagues have spent the last 3 years testing the Direct Aligner photopolymer material from the South Korean 3D printing material company Graphy. Their findings were recently published in Progress in Orthodontics. The team found that controlling material dimensions, structure, and properties of aligners directly—compared to thermoforming plastic sheets—has the potential to make the process of tooth movement faster, less wasteful, and more precise.

  • “If you have a 3D printer, you can now directly print this aligner without having [a] model, without going through the thermoforming process,” said Kim, adding that, with this new FDA approved material, the in-office lab can skip several steps in the current manufacturing workflow, including cutting out the aligners and polishing before delivery to the patient.
  • What’s more, according to Kim, with a direct printed aligner, the clinician can more precisely control the thickness and insert bumps as needed. Kim shared that he and his team found that when the orthodontist can control the thickness they can “control the geometric inside of the aligner.” That, and the ability to add bumps, creates a huge opportunity for the orthodontist because it helps reduce the need for attachments, he said.

For Kim, the shape memory polymer used to make the material is very interesting.

  • He says it somewhat mimics the behavior of NiTi wire. The difference being that a NiTi wire can be exposed to cold temperature to become more flexible, while this Direct Aligner material becomes totally flexible when placed in warm/hot water. The advantage of this shape memory, according to Kim, is that the patient can maintain the shape—and thus the forces—of the aligner at home. Kim points out that patients remove their aligner up to 10 to 20 times a day to eat. “So think about the plastic deformation” every time they remove the aligner, said Kim. But with this material and some warm water, the shape can be restored. Kim uses the analogy of a deformed plastic Coke bottle. Once it’s deformed, it’s not going back to its original shape. But with this material, he can advise patients to put their aligner in warm water at the end of the day if they notice it’s not tight enough. “It will go back to the original shape so they can maintain [a better fit] every day,” he added.

Now when it comes to forces, Kim shares he has been able to apply bigger activations per aligner, thus saving time in treatment and decreasing the number of aligners over the course of treatment. With traditional thermoforming plastics, Kim points out, something like a .5 mm activation per aligner can create a force level that causes the patient too much discomfort and even pain. But with this material, he can avoid that discomfort and pain.

  • “I’m constantly putting .5 mm activations and even 5° rotation per aligner, and then have patients wear [the aligner] just a little bit longer—maybe 2 weeks. Sometimes we go longer,” said Kim, adding that with a standard activation of .25 mm per aligner, to move 1 mm you need four aligners. “But if I can put .5 mm activation per aligner [and] have them wear [it] for 2 weeks, then I need only two aligners.”

In this episode, Kim also talks about the hardware requirements, including 3D printer compatibility with the material needed, and the need for a specific type of curing machine. He also talks about the staging software needed to plan cases using direct 3D-printed aligners. What’s more, he talks about retention and his plans to test an on-site retainer-bending machine from YOAT, a medical technology manufacturer based in Seattle. OP

Podcast Transcript

Alison Werner 0:00
Hi, this is Alison Werner host of the Orthodontic Products podcast. Before we get started with this episode, I wanted to welcome you to our new season and to let you know that if you previously subscribed to the Medqor Podcast Network to keep up with the latest episodes of this podcast, you can now find us and subscribe to this podcast on our standalone channel simply Orthodontic Products. And now let’s get to the episode.

Hello, I’m Alison Werner and this is the orthodontic products podcast today I have with me Dr. Ki Beom Kim, who is the Dr. Lyle Johnston Endowed Chair of orthodontics and program director in the orthodontic department at the Center for Advanced Dental education at the St. Louis University. For the last three years, Dr. Kim has led a research project testing direct 3d printed aligners, the findings of which were recently published in progress in orthodontics under the title forced profile assessment of direct printed aligners versus thermoformed aligners and the effects of non engaged surface patterns. Here’s my conversation with Dr. Kim. Dr. Kim, thanks for joining me today.

Dr. Ki Beom Kim 1:09
Thank you. Thanks for having me.

Alison Werner 1:11
Great, well, so you and your team found that controlling material dimension structure and properties of aligners directly compared to thermoforming plastic sheets can make a difference when it comes to treatment. The first can you talk about the difference between the types, different types of aligner materials that you were dealing with when you were working on this study.

Dr. Ki Beom Kim 1:30
So traditionally, whether you send in your aligners to the big companies or you make in your own in house, or in office aligners, all the aligner has to be made to thermoforming process, you have to make the model first you have to print the model first, and then you suck down with the clear plastics and then cut it out to make the aligners. So we’ve been asking this question for a long time can we directly printed, print the aligners, but in order to do this, this material has to be clear, transparent, that material has to be flexible, and also they have to be durable. And then most importantly, they have to be biocompatible. So these conditions are not very easy to meet. So many companies, they have tried to develop this type of material for a long time. And finally, about three years ago, one of the South Korean company named Graphy, they first introduced this material. So if you have a 3d printer, you can now directly print this aligner without having model without going through the thermoforming process. So if you think about, okay, what could be the most benefit, easily think about the benefit is probably you can save time and money because you don’t or you or your assistant or lab person, they don’t need to print the model. And they don’t need to go to the thermoforming process. And then cut it out the aligners and polishing and deliver it to the patients, if you can directly print an aligner, or you can skip a lot of those unnecessary manufacturing process. So that could be a one big benefit. And the second benefit would be you can save a lot of plastic waste. Because you don’t need to throw those model. And think about all those plastic sheets after you’re cutting out the aligners. Those are has to be thrown away and so you can save a lot of plastic waste. However, the biggest advantage is, is a biomechanical advantage, which that we presented to this progress in orthodontics. Because when you make the thermoforming aligner, you cannot really control the thickness even though your thermoforming plastic sheet is the one uniform thickness. But after you go into the thermoforming process, the thickness of the aligner is different from the incisal edge to the gingival margin. So depending on the patient’s crown lengths and longer crown versus short clinical crown, that dimension is going to be all different. But the printed aligner you can precisely control the thickness, wherever you want. You can make it thicker one side thin on the other side. You can put patterns or you can make the bump inside so that’s the huge biomechanical advantage. So this study we will like to test if we make it thicker to the specified area, can we can we apply more force or optimizing amount of force and also the minimizing the unwanted side effects? That’s the concept we had. And then that’s we we did the test With this material, so it turned out depending on whether you make it thicker or or adding more thickness one way to the other side you can optimizing the force level that we would like to have and also minimizing unwanted side effects. For example, biomechanical rules for fixed braces, if I want to bring the canine down high canine on the upper canine down, if you’re running the small niti wires then as a canine coming down extrude adjacent lateral incisor or first premolar will naturally tipping off they will feel intrusive force because action and counter actions. But whether this is going to happen in the clear aligner, this is we didn’t know actually. But it turned out we using very sophisticated the multi axis the real time three axis force and moment sensor to measure the force. When we apply the aligner with direction of force and then moment not just amount direction as well. We’re going to how the patient’s is going to feel. So it turned out is the clear aligner of biomechanics is a much more complex or complicated than regular fixed braces case. That that was the one of the other findings. So because of the you can control the thickness, you can control the geometric inside of the aligner that will open up the huge opportunity for the orthodontist, because of one aspect is a lot of people especially patients, they don’t like attachment, orthodontics, we don’t like attachment to put it on, right? Nobody likes attachment because a patient’s expecting there’s nothing, they just want a clear plastic, they expect absolutely nothing. But that’s not the reality you put attachment in order to achieve certain types of movement. So the ultimate question is, how can we not using attachment or can we at least minimize of using attachment that was the ultimate goal. So by designing the aligner, instead of putting attachment, if you can make the internal bump, or a lot of people understand is a precious spot like Invisalign, I don’t want to mention the specific name with the company, but there was a something is sticking out inside of the aligner. If I can make it designed as a pressure bump or spot or pressure column shaping into certain direction, we might be able to reduce the number of usage of attachment. For example, if I want to rotate, if I make a bump one side and a slightly different angle to the apogee side, maybe we can create the rotation a moment in order to rotate those canines or premolar. So that was one huge advantage. On top of it. If you think about the removal of plants that were there, class two functional appliances, you can design something on top of this printed aligner occlusal surfaces, you can make the twin block types of pattern, you can print them out, while patients wearing them. They can correct a little bit of class two while they removed some of the crowding or closed spaces. So I think this opened up the huge opportunity and has a big biomechanical advantage for I guess the the scope of the clear aligner therapy. That’s a super exciting about Yeah,

Alison Werner 8:44
yeah. Well, and how Okay, so what are your thoughts on how close we are to orthodontists being able to do implement this in their practice? How far away do you think we are from there?

Dr. Ki Beom Kim 8:57
So in terms of the government regulations, they have FDA approved approval, yeah, this year. So if you want to use it for your patient, you can use it for safe and there are a couple of studies they tested about the size of cytotoxic or safety about this material, they all turned out, it’s a pretty safe to use. And the European market there were a little bit ahead of us. So there are multiple practitioner, they’re actively using this material for patients but in the United States, as far as I know, I’m the only person in the university setting and using it and I have over 100 cases either in treatment or finished treatment now.

Alison Werner 9:47
Okay. And then into so what are you seeing in terms of treatment, how has it impacted your cases and your outcomes?

Dr. Ki Beom Kim 9:56
This particular material has a very interesting properties is because they have is made out of shape memory polymer. It almost act like an niti wire. But the difference is in the niti wire you put it into the cold temperature it become flexible, or that saw, and they heat it up to the body temperature is steepen. So that’s how we use an niti wire, but this material has an opposite direction. So if you put it into the warm water or hot water, it becomes totally flexible. And then it goes temperature goes down, it becomes hardened, so move the teeth. So the how we can take advantage this characteristic is if you have adult patients, a lot of gingival recessions, a lot of undercuts, or patients have a long clinical crown, adult patient, they want to clear aligner therapy then, they’re having a hard time to take the aligner in and out. I mean, that’s very common. So that’s the reason they give out with a little plastic kind of hook to grab it to remove the plastic. So from that aspect, when they heat it up, put like a coffee temperature water it become very flexible, so they put it into your mouth, and then slowly increase the forces so they have more and more comfortable level of force. And also, every time when we eat, we have to remove the aligners. So think about the plastic deformation, how many times patients will remove the aligner per day, probably 10 times 20 times or maybe even more, every time they do they will introduce possible deformation of the aligners. But as you see the plastic cup Coke bottle water bottle basically once once you deform, they’re not going back to the original shape. But this particular material if they feel like they are they’re not tightening or at the end of the day before they go to bed, I recommend to put it into the hot water warm water it will go back to the original shape so they can maintain the better fitting for every day. And then the fourth level also the difference. So we tested the force level. The ideal orthodontic force level should be around 100 to 250 grams of force and some of the tipping intrusive force should be less than 100 grams of force. So when we tested with this, there is another study we published in the progress in orthodontics. thermoforming aligner, has way bigger almost 10 times higher force and printed aligner force. So for example, point three millimeter activation trying to simulate extrusive movement, thermoforming a line or was 1500 grams of force 1500 which is 10 times bigger than ideal level of force, but the aligner was 10 times smaller. So it’s about 150 grams of force. So the force level is much more favorable close to the physiological level of force based on this our study. So from that aspect, this has a gentler or gentle force for the patients and then lasts longer, and it’s much more suitable for the patient’s comfort

Alison Werner 13:28
in terms of printing these these aligns with this material does does the printer make a difference? Or are we talking about kind of the standard printers that most orthodontists would have in their practice at this point? Or is there a different type of technology that’s needed?

Dr. Ki Beom Kim 13:42
I think though these this material has a photocurable so all those different types of printers supposedly they are they should be able to print but if you if they want to have an optimum result obviously you know the car you have you know there are a variety of differences right? So right for us as a university we have three different types of printer SprintRay Pro, which is we started for it works just fine. And then we have Asiga Max, which working fine and then recently, about six months ago we bought another 3d printer unis NV, which is slightly more expensive but it’s much faster three times faster than existing printer. So we are using three and if you already have a 3d printer, and if you want to test it out, I would recommend to reach out to the manufacturer company Graphy, Ask them whether they are existing printer is a compatible. They tested multiple printer they are listed on their website but something very popular here is SprintRay. I think that one is compatible you can you can use that 3d printer. But I do like to mention you have to buy the separate curing machine because this particular material when they need to cure, they have to block the oxygen. So we have a sprintray Pro printer, we have a sprintray Pro Curing box, I tried to use that, because I don’t want to buy the new one, but it did not work because the oxygen presence in the atmospheric oxygen they will combine to this molecule they will penetrate into the into the structure, they will have different types of mechanical property. And also they will loosen up the cross networking structure they will allow the water can absorb easier. So when they when you cure it looks clear from the beginning. But if you’re not blocking the oxygen couple of days after the water gets in, it become cloudy and looks ugly. So you’re not getting the same like the shape memory effect. So I will recommend to buy if you want to use this one in your office, you have to use the oxygen generated the specific curing boxes from there from Graphy.

Alison Werner 16:26
In terms of with the patients you’re treating, have you changed your appointment intervals in any way with this material, or have you seen a change in kind of that treatment progress and how those appointments are structured?

Dr. Ki Beom Kim 16:39
Yes, the, the, the ideal. If I go back to the fixed braces, we put an offer for 14 night I put it in there, we want to leave it for 10 weeks or sometimes 12 weeks, hoping the canine is coming down and the tears are aligned right. But if you if I apply to the clear aligners, we will like to put a bigger activation per aligner. Some companies say you want to have one degree rotation per aligners or point two millimeter activation per aligners, I would like to have a much bigger activation per aligner that will save us time and you can decrease the number of aligners. But the reason why we cannot do that part is if I put for example, point five millimeter activation per aligner, the force level is just too much and patient cannot handle the pain and discomfort. That’s the that’s the problem. So it almost compared to like a stainless steel wire you can put 1925 stainless steel wire from the initial bonding day you had to use a flexible wire right. So the biggest difference of this material is I can put much bigger activation per aligner without creating the huge amount of activation force. So I’m constantly putting point five millimeter activations and even five degree rotation per aligner and then have patients wear just a little bit longer time maybe two weeks, or sometimes go a little longer. So that’s a that’s a big differences. For example, if you want to use a standardized activation amount is point two five millimeter activation. If you want to move one millimeter you need four aligners, but if I can put point five millimeter activation per liner, have them wear for two weeks, then I need only two aligners, so there will cause you know cut half of the aligners. So that’s another advantage. Yes.

Alison Werner 18:45
In terms of doing the setup, when you’re treatment planning, is there anything different from kind of your, from the clinicians perspective in terms of setting up the case on the computer, or in the software to get it to the printer?

Dr. Ki Beom Kim 18:58
This is the most challenging area right now. Because most of the staging software, they’re not designed for printed aligner, or they’re designed for thermoforming process. So I don’t know exactly how far I can push the limit is point five millimeter activation is enough. Can I go a little bit further? And what would be the ideal thickness of this aligner I would like to make it thicker one side, you know, to the other side, I like to make the pressure bump, what dimensions should I do all these things are not 100% clear at this point. And none of the software had this older dysfunction. So I’m using ulab and the ulab they made a special software for us I can make the shell but their their their software is designed for thermoforming process. So if somebody come out with this direct printed aligner module for their staging software, if we can test it more more streamline it, it will be much easier. But at this point, none of the software, so in the European side they have a couple of software they’re already developed. So onyx, onyx sap from Germany, they have this functionality and then delta phase and the other company company, they have those kinds of functionality. But at this point, if you want to use that, you may have to contact a Graphy, they have their own software. So you make the stage model first ulab archforms or any other like a 3shape software, create the arch stage model, and then you import those file into the Graphy software, then you should be able to create the shell because you need to create the shell in order to print.

Alison Werner 20:51
So how do you think direct 3d printed aligners will change the industry and treatment in the next five years? 10 years,

Dr. Ki Beom Kim 21:00
I think it’s going to change our entire industry, because right now we have only one material. But I’m sure a lot of different companies working on it as we have a better material. And we actually optimize amount of activations and dimensions and shape and things like that. It has so much benefit compared to the thermoforming aligners. So I think in five years, maybe I’m just too bold but probably 50% of the clear aligner patients will be using this sometimes these types of technology.

Alison Werner 21:42
Excellent. Well, another area of interest for you is retention. And you’ve been working with a medical technology manufacturer to test an on site retainer bending machine. And you published early results in a study in the angle orthodontist in January 2022. What was your experience with this machine? And what did you find?

Dr. Ki Beom Kim 22:01
So different country they have a different preference in terms of the retainers. I know the European countrie, they really like to use fixed retainer, and I am from South Korea, South Korea, all the orthodontist they like to use a fixed retainer. But in the United States fixed retainer is not very probably preferable because maybe it’s a technique sensitive. And also, maybe the oral hygiene could be an issue. So it’s not as popular as the other country. But the typical process of the fixed retainer from the other country is they take the impression or they do the scan and then send that file to the lab and they have the lab person bend the wire and then deliver it to the orthodontic office and they will deliver it to the patients. Obviously, it’s a time consuming and then also the expensive. So in the United States, a lot of people using just chairside very flimsy and flexible wire to put it on using the dental floss. But there are a lot of actually the case report about unwanted activation. We torqued the wire unwanted activation. So patients ended up having the severe consequences the canine root is coming up from the alveolar bone or something like that. There are lots of case reports. So many orthodontists just pray they will like to use it but they just don’t want something active wire would glue to the patient you are ultimately reliable, right? So this technology is they bend the wire precisely. But if I manually bend, fixed retainer as a manual, I like to bend it in the same plane but that’s not possible because I’m using my finger you’re going to end introducing some of the torque so if that activation is too heavy, eventually couple of years after kids start to move and that you’re going to see the side effects. So this machine is you know, taken away those headaches they will do it for us passively bend the wire in the one plane so you’re not introducing torque at all. So it’s a previous I will say the convenient appointment come to an appointment because before that you take the braces off and you clean everything and then you try and try to fit the wire using the dental floss or holding if i hold it too much you activate the wire right. So there will you have some activate, you will have this active form they will possibly can choose some of the tooth movement but this one is you can bend it in the chair side within five minutes. So typical our process is, before we confirm, I’m going to take this bracket off these patients, we scan with the braces on, and then we put that file into their software, then we can confirm what level I would like to make the fixed retainer. So make sure the lower teeth is not touching the upper incisor and things like that, then we prebended the wire which will take about five minutes less than five minutes. So before we take the braces off, patients come back with a debond appointment, we glue them in first, and then remove the older braces. So it’s a very simple process. And it’s really, really precise and has a big benefit compared to you know, chairside you whether you you’re passively bending or not. But the one very exciting feature with this company right now is we are developing finishing wire bending machine. So you know the suresmile if you want to back in the individual bonded wire, you scan the patient’s teeth and then send it to the company, you have to wait until they deliver the wire. But if you have, the idea is you won’t like to have an in house machine. You scan the teeth when you look at it patients, you know, as an orthodontist, I’m looking at the teeth or I like to bring this bicuspid down half a millimeter I like to put the seven degree tip I’d like to put 10 degree torque even the very seasoned orthodontist how we there is no way we know precisely I can bend those wires precisely. So this machine, hopefully they can accurately bend it for wire for us. In chairside. So it’s why now in works, and I’m expecting to receive the prototype by this fall. And then we’re going to work on that to make it easier for the orthodontist.

Alison Werner 27:02
Well, it seems like so much of your research focuses on digital innovations and how they’re kind of simplifying things for orthodontists but also customizing treatment for the patient. So why do you think this customization is so important today:

Dr. Ki Beom Kim 27:19
You know, the, the, the clinical scale for orthodontist used to be how precisely or fast you can bend the wire from the beginning, then it is move on to how precisely I can put the bracket into the tooth. However, everybody is a different their tooth is different, different shapes, even the right and left side is different. So even the 3d printed customized bracket you still have to bend the wires, because everybody’s different. And we are not just you know, you go to the the mall and buying a suit versus you have a customized a tailor may suit there are totally different. So as our patients wanting to more, they will like to have a more precise and more better than just, you know average treatment. So I think in order to reach the highest treatment goal to make the patients happy and we’d like to make the highest quality of the orthodontic treatment result. I think the customization has to be done. And all the digital technology make us job easier. I don’t think they’re going to replace orthodontist but they will make us job easier for I can precisely prescribe this dimension where how much force I think is going to be the future.

Alison Werner 28:47
Yeah, what excites you about the future of digital orthodontics

Dr. Ki Beom Kim 28:51
a lot of people can or scared about AI. But I can tell you AI is not going to replace orthodontics because AI cannot make the judgment they can make it average judgment they can make us the setup much easier however, is a subtle differences and also the aesthetic part they we will not be replaced by AI. But from the other hand, all the things maybe some tedious setup process or putting the bracket is going to make us so much comfortable and easier for us all those things will technology. So we can see patients less potentially with the remote, you know, the monitoring the tools and things like that, but still maintain the highest quality of orthodontic results. So I think the future of orthodontics is bright and many, many young especially I have a lot of residents. Wow, this is a saturated market and all things like that. But when when we look at the population of the United States, how many people they’re getting braces we are just scratching the surface only and patients want to have better or more as they have a treatment in adolescent adult patient they want to also the treatment. So yeah, future orthodontics, I believe is bright.

Alison Werner 30:16
Well, Dr. Ken, thank you so much for sharing your research and your thoughts on this. It’ll be an exciting future, especially with all these new developments. Thank you.

Dr. Ki Beom Kim 30:24
Thank you so much. Thank you so much.

Alison Werner 30:27
As always, thank you for joining us. Be sure to subscribe to the orthodontic products podcast to keep up with the latest episodes. And be sure to check out orthodontic products to keep up with the latest industry news. Until next time, take care.