Experiments with 3-D printing technology and denture design software bring fully-automated production processes a step closer to reality.
By Dennis Lanier, CDT
How dental laboratories produce the products they make has changed dramatically in the last few years. But now with the ability to integrate technologies, their production capabilities are shifting into overdrive.
Crown and bridge laboratories have had access to digitally-produced, machine-milled end products for more than 25 years, starting with the CEREC inLab® system (Sirona, www.sirona.com). In contrast, the removable side of the business has lagged behind, forced to fabricate full and partial dentures conventionally. However, that all has changed with the new 3-D scanners and denture design software modules recently introduced to the market and integrated with 3-D printing technology.
Sensable Technologies (www.sensable.com) first led the way in the production of digitally designed removable partial dentures, which were printed in wax then cast and fabricated conventionally. But laboratories may soon have many more options for taking denture fabrication to the next level, with the introduction of design software offered by Dental Wings and 3Shape. These open-architecture scanners with powerful new denture design software capabilities will open the door for laboratories to create a fully digital, machine-produced partial-denture product (Figure 1 and Figure 2 ).
Scan, Print, Mill
At The Lab 2000, the new research and design department has been experimenting with integrating these two software modules with 3-D printing and milling technologies as well as new materials to create a direct, digitally manufactured final denture product. The R&D department embarked on a challenge to produce a finished partial denture using 3-D printing and milling technologies with either a rigid or semi-rigid frame, soft or hard tissue (pink), and complete with denture teeth in 24 hours or less.
The first experiments combined digital and conventional fabrication methods. The model was scanned on the 5 series (5-S) Dental Wings scanner (Zahn Dental, www.zahndental.com), and the data file was uploaded to the unit’s partial denture design software module. Next, a unilateral partial that had two clasps and two teeth was designed. The framework data file was sent to the EnvisionTEC Perfactory 3-D printer (Zahn Dental) for printing the partial framework design in wax. The printed wax partial was then scanned and the two teeth that would fit that partial were digitally designed. The tooth design data file was also sent to the 3-D printer to print two full-contour teeth in wax. The partial framework was cast out of metal and using conventional press technology, the two teeth were fabricated with IPS e.max Press ingots (Ivoclar Vivadent, www.ivoclarvivadent.com). Soon users will have the capability to split the files to design the framework and teeth simultaneously.
There was nothing revolutionary with this process so the lab took it a step further to speed production and to eliminate the investing, casting, and pressing processes. This time the same data files were used, but the framework STL file was sent to a Viper SLA (3D Systems, www.3D systems.com) 3-D printing machine and the STL file of the teeth was sent to a CEREC inLab milling machine. (Note: The inLab now accepts data files from 3Shape and Dental Wings scanners.) The framework was 3-D printed, milled, crystallized, and the IPS e.max crown was glazed and attached to the framework (Figure 3 and Figure 4).
The initial trial went so smoothly that the lab decided to produce full-mouth frameworks, upper and lower, from different types of material on four different types of machines using four different technologies: FDM, SLA, DLP, and Polyjet (Figure 5).
Taking It to Another Level
The next experiment involved creating a flexible partial. For this case, denture teeth were placed into the spaces where teeth were missing. The model was scanned and a wax pattern was designed, leaving holes for the natural teeth and denture teeth. The wax pattern was finished, placed back on the model, and the denture teeth put in place. When flasked, the denture teeth stayed in the opposing side when the flask was opened. The wax pattern was then removed, the flask closed and placed into an injection machine.
Thus far, the experimentation still required conventional fabrication techniques. To take production to the next automated production level, the EnvisionTEC Perfactory printer was loaded with the company’s eshell310 tissue-colored material. Designed specifically for use in the hearing aid industry and not yet available for dental use, this CE-certified and Class-IIa material is biocompatible, tough, and water-resistant. Using this material makes it possible to go directly from the CAD partial design to the EnvisionTEC printer for 3-D printing a final product, which eliminates the need for manual flasking, injecting, and finishing.
The final experiment involved creating a rigid or semi-rigid partial framework complete with teeth, using only digital technologies to create the final product. The model was scanned and the file was sent to the software, where the design was completed for the rigid or semi-rigid (controlled by which material is used) partial framework. The file was saved as an STL file. Using that same model file, the tissue portion of the partial was designed, and also saved as a separate STL file. The third component of the partial was the teeth. They can be created in different ways. One way is to set the printed partial framework on the model, set the denture teeth on the model in the correct position, and scan the model, isolating the teeth into sections and saving them as separate STL files. Another way is to make the teeth in the crown and bridge software and import the finished file to the partial software, where it can be manipulated and saved as part of the finished partial.
This time, all three STL file types were sent to the Objet Connex (Objet Geometries, www.objet.com) Polyjet printing machine, which can print different materials simultaneously in a single build. It combines the files and prints the partial framework, the tissue, and the teeth in whatever material the technician chooses in a single-build process. The finished product was certainly acceptable for a temporary (or better) partial denture.
For a more finished final product, the designed denture tooth file scans can be transmitted to a milling machine and full-contour IPS e.max teeth milled to attach to the partial framework using mechanical retention, dual-cure cements, or light-cure Eclipse, depending on which materials are chosen. An alternative method would be to print the denture teeth in wax and conventionally press them, attaching them to the partial in the same way (Figure 6, Figure 7 and Figure 8).
Integrating 3-D printing technology with these new software modules provides incredible flexibility and new services that laboratories can offer their clients. For example, a dentist contacted The Lab 2000 about a patient who did not want to give up his partial while a crown was made under it. The dentist sent the partial to the laboratory while the patient waited. The lab scanned the partial and returned it to the practice for the patient. Next, the scan file was sent to a Stratasys uPrint Plus Fused Deposition Modeling personal printer (Dimension, www.dimensionprinting.com). The complete partial was printed in less than an hour for $1.62. Although this FDM printed partial was not smooth enough for a finished part, it was accurate enough to produce the prescribed crown (Figure 9).
An additional advantage of a digitally produced removable partial or full denture is that the machines can reproduce the exact same product again from a file stored on the lab’s server. This is especially helpful for the elderly or for Alzheimer patients who frequently tend to lose or misplace their removable prostheses.
Adding new products to the lab’s existing offerings is a great way to increase business and make customers happier. The Lab 2000’s latest project from the R&D department is making removable oral prosthetics that have GPS tracking devices that it plans to sell to the military, police, and fire departments.
Now that it is possible to make a removable partial or full denture by machine, the next goal is to make them faster and cheaper.
About the Author
Dennis Lanier, CDT, has been a dental technician for 39 years and is currently general manager of The Lab 2000, Inc. in Columbus, Georgia.