PolyJet Monolithic High-Fidelity Polychromatic Printed Prosthetics

By Robert Kreyer, CDT

It has always been the desire in prosthodontic literature to copy the color, contour, and texture of a patient’s oral soft tissue and dentition when creating complete denture prosthetics. The problem with traditional dentures is clinical data such as impressions, master casts, and relationship records are destroyed during the technical fabrication process. Traditionally, technicians create one-of-a-kind customized dentures but cannot exactly replicate the same fit, function, and esthetics over and over. With progressive CAD/CAM technologies, removable prosthodontics has fulfilled this desire, creating true natural dentures using high dimensional data that is retained for future prosthetics while providing high-fidelity fit and function. This high-fidelity match is accomplished through collected clinical data combined with CAD and CAM using Stratasys PolyJet technology. TrueDent is the first complete denture using a PolyJet additive manufacturing process. TrueDent is an FDA cleared (Class II) resin developed for 3D printing of complete denture prosthetics. TrueDent complete dentures are a full-color, single continuous print of both denture base and teeth, providing the patient with a monolithic polychromatic printed prosthesis.

What is PolyJet?

The key advantage of PolyJet printing is its ability to create monolithic prosthetics using multiple colors and materials with a high-fidelity fit and function on the same build tray (Figure 1). PolyJet additive manufacturing is an amazing technology. PolyJet printers work very similarly to a household inkjet 2D paper printer. Instead of ink, tiny droplets of a UV reactive photopolymer are precisely placed one layer at a time and cured to build a 3D part. The unique way PolyJet printers lay down material allows for blending of base materials into digital materials. An inkjet-type head deposits multiple droplets of a photopolymer onto a build tray. A UV light source immediately cures this layer, and the process is repeated until the part is complete. PolyJet printers have the ability to create more than 500,000 distinguishable color combinations.

In Polyjet 3D printing, the print head is suspended above a build platform. The print head contains several nozzles, as well as a UV lamp. During printing, the print head sweeps over the build tray, ejecting tiny drops of a light-curing polymer onto the printing plate and almost immediately curing it with UV light.

Another CAM differentiator is that PolyJet printing can combine multiple material colors that replicate desired tooth shade, incisal translucency, and gingival base. TrueDent material colors include Cyan, Magenta, Yellow, White, and Clear, along with the TrueDent Support material, which is a hydrophilic plasticized photopolymer.

The remarkable properties of Polyjet technology combined with TrueDent polymer material characteristics, such as the capacity to print a monolithic denture prosthesis; the higher strength of the monolithic structure; and the ability to create internal layered esthetics, position the Stratasys system for success.

Improved Technical Experience

With this capability to print a monolithic pink base and white teeth, conventional manual assembly and bonding for teeth and base are eliminated. Esthetics such as layered shades, base veins or capillaries, opacity, and translucency are determined in software. With future software updates, TrueDent will optimize its capabilities such as multi-layered shades to replicate carded teeth. Imagine having the ability in design to place base colors and tooth shades where desired and then replicating these colors and contours in the PolyJet printing process. “This is just the beginning; dental technicians will have the capability of customizing their own teeth and base shades,” says Stratasys Product Manager Daniel Bahar.

This fast and economical printing is capable of manufacturing an average of approximately 30 full dentures simultaneously, depending on geometry.

A high-fidelity match—down to 18.75-μm layer height and tight tolerances—between design and print ensures repeatable, constant production of accurate, well-fitting dentures. This consistency and predictability in fit and function means less clinical chair-time adjusting dentures, which is a win-win for patients, dentists, and laboratories. Having a high-fidelity match between collected clinical data, design data, and the PolyJet printed TrueDent prosthesis results in an improved denture wearer experience.

In the dental profession, traditional impressions and creating master casts of a patient’s teeth, soft tissue, and edentulous arch has been a costly and labor-intensive process. Fabricating reliable, detailed, and accurate models, diagnostic dentures, and definitive prosthetics is quick and easy with this 3D printing technology. PolyJet dental printers can help reduce costs, streamline workflows, and create dental parts faster and with greater accuracy.

Additive Manufacturing 2023 and Beyond

Until now, printed definitive dentures had to be designed and manufactured in multiple parts and bonded together, such as teeth and denture base. This bonding process introduces variables into the workflow that can contribute to improper relationship of teeth to base pockets and potential de-bonding of teeth. Our goal in prosthodontics is to eliminate variables for successful solutions.

Simultaneous printing of polychromatic parts simplifies the prosthetic production process while increasing efficiency and expanding the prosthetic service offering. With PolyJet printing, the need to change trays for a different tooth or base shade is eliminated. The need to stock liters of material in various denture base and tooth shades will be eliminated as well.

John Madden, CDT, a color consultant in the development of TrueDent, says, “TrueDent is a truly extraordinary product that throws us head-first into the world of full-color dental prosthetics in one print. The denture and temporary crown applications will forever change our industry for the better by pushing digital workflows forward and bending definitions. I am excited to be present for yet another major disruption in dental technology: the full-color revolution.”

These CAD/CAM workflows produce large batches of mixed multi-color parts in a single, unattended print. Shade selection is exported from 3Shape Dental System via 3MF file format to GrabCAD Print and assigned automatically to the printed prosthetic part (Figure 3). With PolyJet, the support structure is created in GrabCAD automatically. Human error of support structure placement is eliminated when using GrabCAD Support software. The gel-like support material (a hydrophilic plasticized photopolymer) is easily removed from the printed denture using a water jet process. Because this gel support material encapsulates the intaglio and cameo denture surface, a true high-fidelity fit is created (Figure 3 and Figure 4).

With this PolyJet technology, we will eventually be able to create characterized complete denture prosthetics that replicate natural dentition, soft tissue colors, and contours. Once this design and color data are in the software, a TrueDent file will be retained so a characterized denture can be replicated exactly, over and over, while not changing the patient’s tooth or base colors, or overall esthetic appearance. The ability to provide a compromised edentulous patient with the same personalized esthetics, function, and fit during their denture-wearing days is truly a game-changer in removable prosthodontic treatment.