The basic understanding of this is pretty easy for dentists to comprehend because we photopolymerize composites every day. The wavelengths of printers are different, but the science is very close and I've always been grateful for that because it makes teaching about 3D printing easier.
One of the things about light curing resins that all dentists are aware of is the presence of an "oxygen inhibition layer" (OIL) which happens during photopolymerization. This happens because:
- Oxygen reacts with free radicals.
- This leaves a thin oxygen-inhibited layer on the surface.
- The result can be a tacky surface, lower surface hardness, and slightly reduced mechanical properties.
The same thing happens with resins in 3D printing. The OIL makes the printed project feel a bit tacky even after final cure. That layer can be removed during polishing, but it requires a bit of extra time because even smooth areas of the 3D printed project need to be polished. Also, with clear projects like occlusal guards or clear ortho retainers it can lead to some discoloration over time.
Until now, there have been two ways to remove the OIL. Complete polishing of the completed project to remove the OIL *or* complete the post-cure process in a unit that provides a "nitrogen only" environment.
Nitrogen curing units flood the post-curing chamber with pure nitrogen before curing. The nitrogen is forced into the chamber, driving out all of the room air that contains oxygen. By curing without the presence of oxygen, the OIL does not form.
The biggest complaints about nitrogen curing have always been:
- Buying nitrogen tanks
- Maintaining regulators
- Replacing cylinders
- Or purchasing a nitrogen generator
While nitrogen post-cure units definitely work (and work well), most require a tank of nitrogen to be connected to them. The tank of nitrogen needs to be purchased and connected. There is also a need for a regulator to decrease the pressure from the nitrogen tank to the curing unit. It's not a huge deal to handle and assemble, but it does make nitrogen post-curing a bit more of a hassle. However, you can purchase a new system that can eliminate the need for nitrogen *and eliminate the OIL* using only light.
That new device is the Rodin Chroma Flash. The Chroma Flash handles things differently. Traditional post-curing devices use high powered LEDs to bathe the project in light to complete the post-cure process. The Chroma Flash uses high energy xenon flash lamps instead of conventional LEDs. Those flashes produce an extremely intense, broad spectrum pulse of approximately 280-950nm. Those flashes deliver tremendous light intensity which drives polymerization very rapidly and very deeply, producing excellent conversion without requiring a nitrogen purge. The easiest way to think about it is that LEDs deliver a lower intensity & longer exposure cure while the xenon flashlamps deliver extremely high intensity for milliseconds repeated many times. That is one of the reasons that flash curing is very common in industrial photopolymerization applications.
The other way Rodin has approached this is with their resin chemistry. Pac-Dent has also developed its materials and surface chemistry to work with this curing method. That means that using Rodin resins with the Chroma Flash unit provides optimized resin chemistry, optimized photo initiators, extremely high-intensity xenon flashes, and carefully controlled cure cycles. Putting all of these factors together makes the Chroma Flash the perfect post-cure unit for Pac-Dent's complete line of Rodin resins.
I'm pretty excited about this new device and I’m on the list to receive a unit as soon as the first ones are here in the US. However, the proof is always going to be in the results. Because of that I'm going to be doing a lot of tinkering and testing with this unit. I'll report back here with my findings and let you know what my take is. 3D printing is making tremendous strides in a lot of areas. Design, resin chemistry, and hardware are all seeing incredible progress. In a few short years we've seen the concept go from "pretty cool" to "clinically relevant" and it only continues to grow.
My prediction is that in less than 5 years, delivery of a large percentage of clinical treatment will be done using things created by 3D printing. In the adoption curve this tech has moved out of "Early Adopter" and has now moved into "Early Majority" and it is only going to keep growing.
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