Dr. Daniel Noorthoek: Hello and welcome to another episode of Beyond the Arches. I'm the host, Dr. Daniel Noorthoek. With me today, I have Robert Odom. Hello. Welcome back, Robert.

Robert Odom: Thank you.

Dr. Daniel Noorthoek: Today we have a very exciting topic. We're going to be talking through all the different materials that you can make hybrid dentures out of, what we've used before, and how we see it in the future. Today we're going to do it a little bit differently. We have in front of us a couple of materials. We're going to kind of go off of sourced information in terms of specific numbers and such. Typically we're more off the cuff and a little bit more informal, but I felt like today, especially as I work with you, that we should probably go through something that's a little bit more historic and linear in terms of what we've used in the past and what the problems were. I'll throw in a bunch of stuff here and there, and your two cents as well, but I thought it would be interesting to kind of walk through some stuff.

Ultimately, we're going to talk about the history of how we got to this briefly, and then the material that kickstarted everything, which was the denture teeth on top of some sort of bar or denture teeth-based prosthesis, and then kind of go into some of the weird ones that we delved into for a while: nano-ceramics on titanium bars. Peak is a material that we used to use a little bit, and then we'll end up on Zirconia and different ways that you can put it on a bar and compare some strengths. Hopefully, we'll have a little bit of fun with it.

Robert Odom: Yeah, love it. As a patient, I think this is one of the most talked-about categories in this whole thing: materials and how they compare to each other and why people choose what they choose.

Dr. Daniel Noorthoek: It's very understandable and relatable that when you're making a purchase that's this big, it's like going out and buying a car. You don't want to buy the latest XYZ that might have more chances of breaking just because it's the latest. You want something that's tried and true, has a track record, but also something that's on the cutting edge. It's hard to balance that, especially when you're trying to explain these things to patients. Hopefully, we can dispel some stuff in terms of materials and just experience what that looks like.

Robert Odom: I think everything has its pros and its cons. You absolutely weigh those options and figure out what's best for each individual.

Dr. Daniel Noorthoek: Every podcast or every lecture that's ever been given on materials always starts with the Egyptians and the gold wire wrapped around a tooth, and then there's the one that's carved out of a seashell, and then there's a joke about George Washington having wooden teeth. So the take-home that I want to give as the history lesson is humans have been messing around with trying to replace teeth that have been missing for a really long time. Finally, after many different attempts, we are at a position where we can talk about specific different materials rather than just "let's try this new thing and see if this works." Now we can actually make a comparison and say, "Is this better or is this better?" rather than just "Does it even work?"

We're not going to go through that part of the history because I feel like it's a really overdone trope, but if somebody would like us to go through all of that, we could do one specifically on ancient restorations.

The story starts with cast bars that had denture teeth put on top. There were some other things that came along before this, like the advent of material called Vitalium and Palladium that gave us the ability to make denture bases for partial dentures. When you make a full denture, it can be made out of plastic because it doesn't need to hold on to anything but gum tissue; the force you can put on is only as good as your gum tissue. But when you're going to attach it to other teeth, it needs some sort of wiring and reinforcement to grab onto other teeth. That was probably the original drive to start adding tooth-like plasticky materials to metal.

Fast forward to when dental implants started being used. We refer to them as endosseous dental implants, meaning "within the bone." In the 80s and 90s, they started to figure out how to attach these to metal reinforcement. That lasted quite a while. We were still producing those when I first started on the full arch scene between 2010 and 2013.

Robert Odom: I don't know anything about the process of making a cast bar. I've got so many questions.

Dr. Daniel Noorthoek: To make a cast anything, you have to make a duplicate version out of material like Durlon. You put it in a furnace and you melt the gold or whatever metal alloy you're using and it spins it into the cast in a huge spinning furnace. Back then, we didn't have milling machines or the computer power. We had to go through long procedures to get good impressions so the lab could build, wax, and mold your custom bar to hold onto your implants. It took artistic hand skills on both the dentist and the lab side.

Back in the day, we had to make sure those implants were exactly in the right position. We used a "verification jig." We would take analogs and glue them together in the mouth with a thick worm of material, then cut them in between the implants. Stone model material shrinks and deforms when it hardens, so I can't take an impression, pour it in stone, and have it be an exact replica enough to put metal in your head. We would try in the segmented parts, glue them back together, and that would accommodate for the shift. If it wouldn't fit, you'd have to cut the stone model apart and refix it.

Once that part was done, you would create a model in wax of where you wanted the teeth, very similar to a denture. You’d shape it to push the lip out properly and get the vertical dimension right. Then you would mark the midline. We're now four or five visits in and the patient is ready to go crazy on your office.

The lab would put the teeth in wax and send it back. If something was slightly off, you could push the tooth because it was in wax. But generally, by then, they've incorporated the bar. The made metal bar with the wax teeth would often end up in a place that was so bizarre relative to the teeth that we ended up with a lot of speech problems and complaints that the temporary was better because it wasn't as bulky.

The funniest and worst thing was if it was in the patient's mouth too long—like if they had to go to the waiting room to get approval from a spouse—the body heat would start to melt the wax and the teeth would start mushing off to the side. You had to keep a bowl of ice to the side. After that was done, the lab would process it by replacing that wax with acrylic plastic under vacuum pressure.

Besides being clunky, long-term these didn't hold up past 10 to 20 years because plastic really wasn't intended to hold the weight of smashing sets of teeth together against metal. You got a lot of fracturing and debonding. Biomaterials is all about the sweet spot between rigidity and flexure. If you have too much flex on top of something that doesn't flex, it breaks. We saw that all the time.

We still see these occasionally from the 90s. I think we did one a year or two ago for a lady who had worn hers for 30 years. They held up well for her, so you can't talk too bad about them—they were what this whole niche of dentistry was built on.

Dr. Daniel Noorthoek: Then we got milled bars. We could take a stone model and convert it digitally using a tabletop scanner. That turned into a digital record. We would digitally create or replicate the bar. They were milled out of one piece of metal. It was always really fun to watch the milling machine cut that metal.

Then what we put on top changed. We started putting PMMA (polymethyl methacrylate) on top of titanium bars. The idea was that the patient would get a "retread," meaning they would get a new set of teeth cemented on top of the bar after a few years. But these weren't that strong because you're dealing with unlike materials against each other with different flexural strengths. Long term, you had problems with bacteria collection and porosity. These materials can stink and stain.

So we switched to nano-ceramic. My business partner at the time was sold on how nano-ceramic was the newest and greatest thing. It was plastic filled with chunks of micro-ceramic. The pitch was that it was stronger, less porous, and "repairable chairside."

Robert Odom: That's great, but I'd rather have something that didn't need to be repaired in the first place. I don't want "Fix-a-Flat" in my car; I just want a car that doesn't break down.

Dr. Daniel Noorthoek: Nano-ceramics were not strong enough to be their own piece; they needed a bar underneath. At that time, we were able to design a fit between the bar and the prosthesis at around 20 microns. That was the first time we could remember putting teeth in and having almost no bite issues. But according to preparation for this, there were a lot of failures reported at the 2-to-5-year mark.

When we started to see failures, we scrambled to figure out why. The industry theory was that the titanium bar had no flexibility, which was causing the brittle nano-ceramic to break. So the industry switched the bar material to Trilor or Peak, which are fiber-reinforced plastics. The theory was they would flex as nicely as the nano-ceramic. The problem was those fiber-reinforced bars take up so much room for strength that the nano-ceramic is now just a thin little shell on top. When they fractured, it was a devastating explosion.

Also, if you skip the titanium bases that hold onto the implants to save a step, the material would commonly strip out over time when you put the screw in. Peak is a very rubbery plastic material.

Robert Odom: You could feel it when you started to screw in; it would give a little bit.

Dr. Daniel Noorthoek: Personally, we ended up having to replace all of these at our cost because they were under warranty. I believe it was somewhere between $250,000 and $500,000 that came out of my pocket to replace those failed nano-ceramic teeth. If anyone hates nano-ceramic on this planet, I'm the guy. It was supposed to be vetted, but when the problems accumulated, the material company didn't stand behind anything.

Robert Odom: I had my procedure done when you were using nano-ceramics. I research stuff, and my biases were confirmed by reading that it was the best material ever. When I started having problems, I thought it was my fault. I thought, "What am I doing wrong?" I omitted any kind of hard food. But even my second set started staining before the 12-month mark. I don't know how anybody continues to use it. I was in nano-ceramics for a total of three years before transitioning to Zirconia.

Dr. Daniel Noorthoek: We’ve been in Zirconia full-time since about 2019. Early Zirconia looked like a piece of chalk—very opaque and lifeless. But as the smartphone market exploded, attention went to screen tech; similarly, as Zirconia became a hot trend, manufacturers started making pucks thick enough with built-in translucency at the bottom. Now you get strength, look, and performance in one piece.

There is a restoration in vogue right now with a titanium bar underneath a Zirconia overlay. That scares the bejesus out of me because I was so burned on the nano-ceramic world. You’re back to relying on cement and materials that flex at different rates.

Robert Odom: If monolithic works so well, what is the alleged benefit of combining two materials?

Dr. Daniel Noorthoek: My theory is that the industry likes the titanium bar because you can get away with some inaccuracies—they are all hooked together, so it doesn't transfer as much force into the Zirconia and fracture it. But we take care of that with our scanners.

One of the first Zirconias we ever put in around 2016 was for a traveling nurse going to Hawaii. As we put it in, something must have been tweaked off, and when we torqued it in, the thing shattered. It feels like what I imagine breaking a bone feels like—that sinking gut feeling. Monolithic Zirconia doesn't tolerate being anything other than perfect. That’s why we use scanners to get perfect data for a passive fit.

Let's look at flexural strength:

• Nano-ceramic on Titanium bar: Low hundreds of megapascals.
• Peak framework with nano-ceramic veneer: 200 megapascals.
• Titanium bar with individual Zirconia crowns: 900 to 1,200 megapascals.
• Monolithic Zirconia: 850 to 1,100 megapascals.

If the strength of monolithic is comparable to individual crowns, but man-hours are diminished and the look is better, it improves predictability, efficiency, and price for the patient.

Dr. Daniel Noorthoek: The future is probably printing. Milling is subtractive; printing is additive. They are polar opposites. Milling starts with a solid puck and removes material; printing builds it. milling has waste; printing has virtually zero.

Even if you don't care about the planet, less waste means more efficiency and speed. I'm very excited about that future. If I don't have to hire as many ceramists, we can focus more on polishing. Currently, printable material is still plastic-based, so porosity and staining are still issues. But in 5 to 10 years, when it's accurate and beautiful, it'll be sweet.

Imagine a subscription model. Every time you come in for a cleaning, you get a new set of teeth. If you want something changed, we just change it on the computer and have brand new teeth in two hours. You could think of the teeth as a little more disposable if they perform to our standards.

Robert Odom: There are certain shapes of teeth that represent youthfulness, like pointed canines. Over your life, you wear down your teeth into a squared look. Someone who has this done at 30 may want that youthful look, and then 20 years later, they might want a more natural, mature smile. To have that option is super cool.

Dr. Daniel Noorthoek: That is fascinating. Zirconia still has graze lines or craze lines sometimes from manufacturing, but printing will solve that. When you're milling, getting certain angles is very hard. With printing, the world is your oyster. I’m excited to see the internal lattices and shapes that will add strength and transparency inside the hybrid.

I can guarantee you we aren't even a year out from a magical print change, but when it happens, we will make it an attractive switchover for our patient base at a low cost. For now, Zirconia is the sweet spot. Robert, I appreciate your time. I nerd out on this stuff even more than surgery.

Robert Odom: Thanks for having me.

Dr. Daniel Noorthoek: We’ll see you guys next time.