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Digital Denture Technology Ready for Widespread Use
Laboratories need to understand the various options on the market
Alexander Wünsche, CDT
Digital dentures offer numerous benefits that often include a high level of consistency, economic efficiency, and cleanliness for both laboratories and dental practices. Digitization can be applied to one, several, or all of the steps involved in the process, including scanning, designing, printing try-ins, and milling the final prosthesis. 3D printing can be utilized for various parts of the process and some solution providers offer a complete 3D printed long-term final digital denture option; multiple 3D printer manufacturers and 3D printing material vendors offer their solutions in collaboration with various CAD software providers. Partial denture framework and implant-retained denture producers are among the earlier adopters of digital workflows in the removable space, significantly due to the inherent benefits and indications that digital technology can provide.
Despite this advanced technology, fewer than 15% of dental laboratories in the US produce any digitally manufactured full dentures, according to the National Association of Dental Laboratories. This is not because the technology is inadequate. While there is room for improvement, the slow rate of adoption can be attributed to a need for more education on the wide variety of design and fabrication possibilities, just as in the early days of CAD/CAM for fixed restorations.
Various workflows exist, and the process of selecting the best one(s) for your business can be tedious, especially for small or medium-sized laboratories. Implementing digital processes just because they are available is not a prudent business decision; laboratories must evaluate whether a process is really beneficial in order to adopt, leading to greater efficiency and effectiveness compared with existing analog workflows.
Degrees of Digitization
The various digital denture workflows include different degrees of digitization. Some systems are fully digital, from the patient's first visit to the laboratory procedures to the finished product. For example, the Baltic Denture System (BDS) from Merz Dental entails scanning an impression using their specialized technique and tray, and fabricating a milled denture from a pink and white monoblock that only requires polishing and adjustments at the end. No model is necessary. It is a truly digital workflow in the laboratory.
AvaDent Digital Dental Solutions and Dentsply Sirona Digital Dentures offer digital outsourcing solutions, ranging from CAD services to fabrication of the try-in and/or final denture by AvaDent. For laboratories wishing to mill in-house, AvaDent and Dentsply Sirona provide materials.
Custom Milling Center also has introduced a new printed digital denture solution that the company says makes it easy and affordable for every laboratory to offer a digital denture.
Hybrid systems such as Amann Girrbach's Ceramill FDS (Full Denture System) and Kulzer's Pala Digital Dentures utilize CAD/CAM for the try-in phase but have the option of analog fabrication for the final denture.
The Ceramill FDS process allows for the dentist to take either analog or digital records and for the final denture to be fabricated traditionally. However, in between those steps, a model is scanned and the try-in is digitally designed and milled. The Ceramill system offers the ability to use VITA stock teeth and mill the intaglio side to fit seamlessly into the milled denture base. It also can be used in conjunction with Merz's BDS.
Ivoclar Vivadent's system is similar to Amann Girrbach's in that analog records can be combined with a digital try-in. Ivoclar Vivadent also provides proprietary pucks from which the laboratory can mill a denture base and denture teeth. The teeth can be milled as individuals or whole tooth segments, which is preferred for ease of post-process bonding to the IvoBase CAD disc.
Kulzer's Pala system, meanwhile, utilizes a 3D printed try-in and now offers the option of a Pala 3D Printed Denture with FDA-cleared materials for the denture base and denture teeth.
Besides full dentures, the digital world also offers solutions for partials and implant-retained dentures. Partial modules from all of the major CAD software systems are already available and being utilized for printing resin partials to cast in chrome cobalt. A newer method to fabricate digital partials is to mill the framework with high-performance polymers, such as Solvay Dental 360's Ultaire AKP, anaxdent North America's Pekkton, or JUVORA Dental's PEEK-OPTIMA. These materials promise longevity for partials that extends far longer than a temporary phase. The main concern is to create a long-lasting bond between the denture teeth and the polymers, so certain techniques are crucial to fabricating a successful digital partial denture.
Implant-retained digital solutions offer strong possibilities. Hybrid solutions allow the analog processing of the digital denture after the try-in phase, so components such as implant bars or attachments can be processed into the acrylic. The implant side of dentures can benefit significantly from digital processes because of the ability to start with digital implant planning and a surgical guide before transferring the data into the digital denture design. The most significant advantage is that the workflow for immediate-load cases is becoming very smooth, and many parts of the restoration can be fabricated prior to surgery.
While these solutions have become somewhat established, manufacturers continue to innovate.
Kulzer recently made its proprietary jig tool available for in-house denture fabrication after utilizing it for several years as part of the Pala system and also introduced new FDA-cleared 3D print base shades. If basal reduction is necessary after a case has been designed, the tooth jig or reduction coping for the ridge can be fabricated, the teeth can be placed in there, and they can then be removed to be processed in whatever format is desired.
AvaDent has introduced the AccelerSet solution for fixed hybrid dentures. This solution comprises individually milled lithium disilicate or zirconia crowns, a milled titanium bar, and a milled pink acrylic base that are all designed and fabricated simultaneously.
Merz offers the BDKEY Set as part of the Baltic Denture System. The patient-specific size of the PMMA BDKEY is determined by using the PEEK Upper- and LowerKEY. The PMMA Upper- and LowerKEY and the BDKEY Lock are then used for the functional impression by applying BDImpress to check the esthetics of the try-in and to determine the correct position of the occlusal plane.
To drive and develop digital dentures and make workflows better, companies are partnering together for better results in many instances. For example, Carbon offers its 3D printed denture solution in conjunction with 3Shape's digital denture module; EnvisionTEC and 3DSystems, too, offer a 3D printed digital denture output workflow. Additionally, certain third-party design companies offer CAD services for dentures, whereby the laboratory simply digitizes (scans) the case and sends the files. After reviewing the design, the laboratory can download it and fabricate the final dentures.
This workflow is especially helpful for immediate dentures, because it is very economical and fast. Also, the quality is relatively high, largely because the materials are validated and work together well. The bonding process of the printed teeth into the base is not based on a third-party bonder as with milled dentures; it is photo-polymerized resin, identical to the printed denture that is light-cured together, so both parts become one.
Various other 3D printers also can be used to print the denture base—designed with exocad, 3Shape, or other software—with real denture teeth or printed/milled teeth bonded into place.
One of the primary challenges to a fully digital system is the fact that intraoral impression scanning currently does not accurately capture soft tissue compression, which many believe is necessary in order for a denture to fit well. For any denture workflow that begins with a digital scan, at some point a wash impression likely will be necessary to reline the denture for soft tissue compression. Some systems capture that information when the initial impression is taken, using unique techniques, trays, and silicone materials, but an intraoral scan workflow may require that step at some point after the denture has already been processed. In the future, a more comprehensive solution likely will be available, whether via technology that captures the soft tissue compression digitally or new materials that do not require consideration of soft tissue compression.
Digital denture software options continue to improve as well. For example, it is now possible to mill the intaglio surface of a denture to make it fit in the ridge, or to print real tooth molds to fit the mold socket in a printed base.
One of the most significant challenges still to be addressed involves fabricating a digital denture for only one arch. Most edentulous or partially edentulous patients have malocclusion issues, so it is very difficult to digitally design a denture for one arch that will fit the other arch well. The teeth must be set in a certain way, and occlusion must be adjusted.
Developments in 3D printing will have the most significant impact on digital dentures because of the economic and efficiency benefits. While 3D printing is currently not as consistent as milling for dentures, wax bases, and other components, it is a much less wasteful workflow.
The primary reason for the inconsistency is the resins; the curing process takes time for a printed resin, and during that time, expansion and shrinkage occur. Additionally, printed resins are relatively porous, which creates an inconsistent workflow because of varying levels of porosity. That porosity also makes the final product less durable than a PMMA or acrylic restoration. Printed resins also are slightly more difficult to reline, and adding any type of composite or acrylic is tougher as well. If a repair or reline is necessary, achieving a bond between the materials is more difficult, so technicians need to know how to treat the surface correctly.
Achieving the highest level of esthetics from a pink monoblock will always pose a major challenge because natural gingiva is not one color. Making the gingiva appear authentic requires a significant amount of time with composites or light-cured glaze and stain kits.
However, new printing technology may address this issue, and regardless, esthetics are always a matter of personal preference. Dentures that do not meet the standards of a high-end dentist or technician may make the patient very happy. They may not be perfect, but they are still highly esthetic and the patient is able to chew again. It is always necessary to keep that in mind when weighing the advantages and disadvantages of different workflows.
CAD/CAM fabrication is likely to become as prevalent for removables as it is for fixed in the next 3 to 5 years. 3D printing will play a major role because most dentures will be, more or less, a result of mass production due to economics.
While the patient's finances typically are a primary factor, it is important that we not lose the human touch. As manufacturers continue to innovate with materials, equipment, and software, technicians must continue to develop better techniques for making these dentures as esthetic and functionally strong as possible.
About the Author
Alexander Wünsche, CDT, is the President of Zahntechnique in Miami, Florida.