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Clinicians and laboratory technicians are aware of the many issues surrounding conventional production methods for removable prosthetics. The process of manually designing and fabricating removable prosthetics is lengthy, inconsistent, and complicated,1 and most often, it is the patient who must demonstrate the greatest level of tolerance. As digital dental technology evolves, it will drive a full-mouth platform that includes full and partial dentures in a controlled digital production process.
Manually prepared prosthetic devices, by the very nature of human involvement, are prone to mistakes, and are developed with an inherent margin for error. Despite the advancements in technology, the materials involved in denture manufacturing in the existing process have inaccuracies in the natural curing of the acrylic product, which creates inexactness. To compound the issue, there is no concrete standard of good, better, or excellent in the dental laboratory industry. Each facility creates its own set of standards independent of any industry codification.
For example, multiple methods are available to clinicians for organizing their final patient records. This poses an obvious challenge to streamlining record-taking procedures to any real degree, even among the same group of practitioners, and especially among industry groups. The root of the problem lies in the current lack of an industry definition on what processes can be identified as good, better, or excellent. What is “best” for one laboratory could result in an inaccurate or ill-fitting prosthetic, and at the same time, a prosthetic delivered by another laboratory that considers the “best methodology” to be the traditional injected process could produce exactly the same results. Creating overall and coded standards in dental laboratories may be difficult to consider and execute. However, CAD/CAM software can and does standardize the process not only with an algorithmic solution to minimize functional human inaccuracy in setup, but also by establishing a standard for materials that are used in subtractive or additive processes.2
Today, digital processes for creating wax patterns for cast partial denture frameworks, milled or 3D-printed full-arch denture bases, or laser-sintered metal partial frameworks have been introduced that promise to remove the inaccuracies inherent in the manual production of removable prosthetics.3 Whether using a subtractive or additive production process, both are only as good as the acrylic material being processed and the record taking used for the design. Both processes decrease material shrinkage and use materials that are more biocompatible than conventional materials.
Clinical Protocol Business Model
Practitioners know that without a good record, any possible changes taking place in the patient's mouth could result in a low-grade denture when completed. This, along with a host of other possibilities, could spark fitting problems, nearly all of which could be resolved or even eliminated with the use of the design and preparation capabilities and processes of CAD/CAM technology (Figure 1 through Figure 3).
AvaDent® Digital Dentures (Global Dental Science, LLC, avadent.com) and Heraeus Kulzer's Pala Digital Dentures (Heraeus Kulzer, paladigitaldentures.com) are the only two digital processes on the market today with clinical inputs for creating a digitally produced full denture (Figure 4).4 Because the patient record is the control for the standard of care, both companies have developed uniform record-taking processes. AvaDent has several options to record vertical dimension and centric relation (CR). One of those devices is an anatomical measuring device (AMD) (Figure 5) and thermoplastic custom tray for duplicating the unique characteristics of the gingival surface for record taking, while Pala Digital Dentures provides maxillary and mandibular impression trays.
AvaDent's AMD captures the occlusion of vertical dimension (OVD) as well as the CR of the patient. It also has an intraoral adjusting screw to record vertical height, CR, lip support, bite plane midline, smile line, and central incisal line. The AvaDent process merges the digitized final impression with the digitized record device, which gives full control over the thermoplastic tray, and a qualified, full oral-cavity record-keeping system. This method means having an overall, calibrated edentulous report suitable for a predictable restoration.
The clinical aspect of Pala Digital Dentures is based on the maxillary and mandibular tray it uses for the impression and for record taking. The trays have an occlusal OVD screw that is hand-manipulated to capture the OVD. This screw also acts as a tracer to capture the CR movement. The standardized tray is sent to the Pala Digital Dentures production center, where the company manufactures a 3D-printed denture try-in and/or processes the final product (Figure 6).
Both companies offer laboratories the opportunity to be certified by the company. The certification includes use of proprietary interaction with the software.
The AvaDent digital workflow for the laboratory is as follows: 1) The dentist sends the laboratory the AvaDent AMD record; 2) The laboratory scans the AMD and uploads the digital file into the proprietary AvaDent CAD software, and sends the file to the AvaDent design station; 3) The file is emailed to the central design and output center in Scottsdale, AZ.
After receiving the fully digitized AvaDent design file, the in-house laboratory performs a quality control check, reconfigures the setup if necessary, and finalizes the design. Following final approval of setup from the in-house laboratory technical staff, AvaDent manufactures the final output in a modeless approach and sends it to the participating laboratory.
AvaDent offers multiple outputs for participating laboratories, including scanning and bone reduction guides, a provisional denture, a milled base with a wax-teeth try-in denture, a complete denture, an implant conversion denture, and an implant hybrid prosthetic.
The Pala Digital Dentures digital workflow in the laboratory also begins with receiving the impression record from the dentist. The impression is scanned by the laboratory, the scan file converted to STL format, and then the digital file uploaded to the Pala Digital Dentures portal for digital modeling and articulation using proprietary CAD software. A 3D printed try-in is produced and sent to the laboratory for review and then passed on to the dentist. Once the try-in is approved by the dentist-client, a final prosthesis is manufactured using a proprietary injection process and sent to the laboratory for delivery of the final prosthesis to the dentist.
As the demand for digital dentures increases, consumers, providers, and manufacturers have a laundry list of elements to consider during the planning, production, and patient placement phases. A significant note to this set of circumstances is that currently, there is no laboratory system in place with the centralized production business model that provides complete control over the workflow process.
In-House Full and Partial Denture Production
Several companies now provide laboratories with CAD software modules for partial and full-arch denture design and the output materials and processes for additive production of partial frameworks combined with conventional in-house processes for production of metal-based partial dentures or production center additive manufacture of end-use metal or flexible partial dentures and full-arch removable prosthetics. As an emerging technology, new material developments and inputs and outputs for producing the physical product are still in their infancy.5
In terms of CAD software modules for the design aspect of producing full dentures, Dental Wings is now providing an easy and efficient way to digitally design full dentures via its DWOS Full Dentures module. The CAD software module offers intuitive tools to help the dental technician execute a familiar workflow in the digital environment in less time, and take advantage of the highly esthetic automatic tooth arrangement proposal. Output is a 3D-printed or CAM-milled denture base made available to laboratories through a centralized production center.
Exocad (exocad® DentalCAD, exocad.com) offers a denture CAD module with one formal input through supported systems such as the Amann Girrbach Ceramill Mind CAD software system (Amann Girrbach, amanngirrbach.com), which is based on the traditional base plate and interior setup method and offers outputs for the final product.
The 3Shape CAD Denture Design module (3Shape Dental System™, 3shape.com) implements a traditional wax rim input with 3D printing or milling technology output.
EnvisionTEC (envisiontec.com) has demonstrated a laboratory-driven 3D printing production process and the materials to print a denture base using the company's ULTRA® or Perfactory® DDP4 printers. The denture teeth can be printed separately using the company's E-Dent composite material and bonded into the denture base.
For the production of partial denture frameworks, different digital production models exist from CAD design and traditional casting from a 3D-printed wax pattern to a fully digital process using metal laser-sintering technology.
Conclusion
The digital dentistry platform for full-mouth rehabilitation will soon be standard in the industry, and include the digital design and manufacturing of both mucosa-supported and implant-supported full dentures. Soon all modules will be able to accept standard STL files from all open-input devices, including digital intraoral impressions, scanned models, and scanned impressions. These platforms will support all relevant output devices, such as 3D rapid manufacturing printers and various milling systems.
In the future, full-mouth functional digital prosthetics will contain complete digitized denture tooth libraries from various denture teeth manufacturers.
The application will be seamlessly integrated with the screw-retained bar and bridge function. The ability to design prosthetically driven implant bars based on the simultaneous virtual denture design propositions will allow laboratory technicians to achieve an advanced degree of functionality and esthetics. This integration will enable technicians to design and fabricate dentures supported directly on locator type implant interfaces. Each of these technologies will have its own level of efficiencies and cost savings for both patient and practitioner.
That said, education will always be the most important factor for the success of a system in the clinical environment. With the rapid advances in today's rapid prototyping and milling technology and the focus of new technicians on being digital problem solvers, new advancements in this arena will be on the horizon.
This article is a brief overview of the interfaces that are currently in use and delivering proven innovations and solutions to the dental market. It is clear that full-mouth rehabilitation and processes in the removable prosthetic dental laboratory industry could definitely benefit from establishing a set of uniform standards; digital technology is the ideal method for creating those standards. Using full digital outputs, the industry can not only create better removable prosthetics but also establish a standard process that influences the method of full-mouth rehabilitation.
Further developments and advancements in workflow and software processes will help simplify and standardize these outputs in the future. Digital methods facilitate excellent communications while simplifying the denture process. The win-wins for the end-user, clinician, and dental laboratories are improved information, selection precision, efficiencies, improved esthetics, and increased patient satisfaction. One thing the industry can count on is that more changes and advancements are on the horizon.
References
1. Yuan FS, Sun YC, Wang Y, Lü PJ. Accuracy evaluation of a new three-dimensional reproduction method of edentulous dental casts, and wax occlusion rims with jaw relation. Int J Oral Sci. 2013;5(3):155-161.
2. AvaLozada JL, Garbacea A, Goodacre CJ, Kattadiyil MT. Use of a digitally planned and fabricated mandibular complete denture for easy conversion to an immediately loaded provisional fixed complete denture. Part 1. Planning and surgical phase. Int J Prosthodont. 2014;27(5):417-421.
3. Tripodakis AP, Gousias HC, Andritsakis PD, Tripodaki EA. Evaluation of alternative approaches in designing CAD/CAM frameworks for fixed partial dentures. Eur J Esthet Dent. 2013;8(4):546-556.
4. Kattadiyil MT, Goodacre CJ, Baba NZ. CAD/CAM complete dentures: a review of two commercial fabrication systems. J Calif Dent Assoc. 2013;41(6):407-416.
5. Bidra AS, Taylor TD, Agar JR. Computer-aided technology for fabricating complete dentures: systematic review of historical background, current status, and future perspectives. J Prosthet Dent. 2013;109(6):361-366.
About the authors
Andy Jakson, CDT
President
Evolution Dental Science
Buffalo, NY
Joshua Jakson
CAD/CAM Manager
Evolution Dental Science
Buffalo, NY
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