Digital Transformation of Denture Workflows
This is the third part of IDT’s ongoing digital denture series by Robert Kreyer.
Robert Kreyer, CDT
Digital workflow solutions are truly transforming clinical and technical treatment options for complete denture prosthetics. Conventional workflow processes utilizing equipment and materials that have been used in removable prosthetics for the last century are slowly being replaced by digital technology. With the dramatic increase in adoption of digital technology in dentistry, three basic workflows have emerged for complete prosthetics: conventional, digital, and integrated treatment solutions for edentulous patients.
The conventional workflow as we know it has two clinical options: a linear process or a branching process that utilizes materials, equipment, and techniques that have been used and proven over the last 100 years. Linear and branching techniques were first discussed by Earl Pound, DDS, in "Introduction to Denture Simplification" (1971).1 The linear technique follows specific steps, starting with diagnosis, then fabrication, and ending with a final complete denture. The branching technique is progressive where diagnostic information is gathered during the use of a treatment denture. The accumulated clinical denture data sets are used to further develop and create a definitive denture according to information discovered through diagnostic treatment. Conventional denture workflows do not retain collected clinical prosthetic data or information. For example, a baseplate and contoured occlusal rim have clinical information about the vertical dimension, centric relation or myocentric position, arch form, midline, high lip line, and buccal corridor. All this collected clinical information is destroyed when teeth are arranged on a baseplate unless a new baseplate is used to preserve record data or a matrix of the rim is made. With a conventional workflow when a patient loses or needs a new complete denture the clinical process starts from the beginning, unlike a digital workflow where it starts from the last archived file. Nonetheless, conventional workflows will remain in use for many years until clinicians, educated in digital workflows, demand alternative solutions using progressive technologies.
The digital workflow is the emerging technology that provides prosthetic solutions based on collected clinical data needed for the computer-aided design (CAD) phase where clinical outcomes are achieved through sophisticated computer-aided engineering (CAE) algorithms. CAE incorporates mathematical algorithms to control and assist the design and manufacturing of a dental prosthesis or digital denture. CAE is used to automate most of the work that has traditionally been done by the technician in crafting a conventional complete prosthesis, such as identification of edentulous anatomical landmarks, model trimming, registration of digital models, teeth set-up and creation of proper functional occlusion, generation of denture base and gingival contours, and preprocessing data for computer-aided manufacturing (CAM). CAE insures that the digital model follows correct clinical rules established by the profession. An advantage to a digital workflow is that a linear or branching clinical process is still used while all the collected clinical data sets are preserved and can be used throughout the design and manufacturing process. This includes transparency overlays for confirmation of registered clinical data. The archived digital denture data is used for future complete prosthetic treatment, saving hours of clinical chairtime.
Integrated workflow is used when the treatment solutions will include both conventional and digital workflows, as required based on the patient's prosthetic variables. This integrated workflow solution is used for complex restorative cases such as implant-supported prosthetics or when a patient's expectations and desires cannot be achieved with a single workflow solution. Integrated workflows have been used for years with digitally designed and milled implant bars. The advantage of an integrated workflow is creating conventional border-molded impressions, records, and try-ins, then scanning to create a digital file which records the approved tooth arrangement data as a digital design reference that will be used in the remaining digital workflow. The denture is then transitioned from conventional to digital workflow after confirmation and approval of records, esthetics, fit, and functional occlusion. The digital file of the denture then goes into the CAM phase for either a subtractive or additive workflow process. This digital file provides the clinician and edentulous patient with the data or information needed about their denture for future prosthetic needs.
The objective of denture diagnostics is to understand all the variables that exist in the patient's current prosthetic condition. After analyzing these variables, we must develop a case or treatment plan that will provide a prosthetic solution for the compromised edentulous patient.
Conventionally, dental technicians would create study casts, mount with records on a dental articulator to analyze the prosthetic space, then design a complete denture prosthesis. During this conventional analysis, the team could view the facial, buccal, posterior, and occlusal views of the mounted study casts. Laboratories would have to traditionally set and wax teeth into their proposed position to provide a diagnostic tooth arrangement to achieve a functional occlusion. These mounted study casts would then have to be shipped to a clinician for review and approval of the proposed complete prosthetic plan.
An advantage of a digital workflow for diagnostics is the ability to view terminal dentition, ridge relationship, prosthetic condition, prosthetic space, anatomical landmarks, anterior esthetics, and functional occlusion in various perspectives before treatment has begun. The digital denture design files can then be arranged in a sequential treatment plan proposal and emailed to the clinician for a collaborative discussion with the clinical team and the patient. This saves time as well as improves communication and collaboration among technician, clinician, and patient.
Traditional border-molded impressions are still the best and most time-proven way to capture all soft tissue anatomical structures within the denture space (Figure 1 through Figure 5). For conventional, digital, and integrated workflows, this border-molded impression is essential to a properly fitting and functioning complete denture.
The advantages of scanning an impression or cast into a digital workflow is the ability to zoom in on soft tissue anatomy for confirmation that the impression has captured all the necessary anatomical landmarks. If there are any questions, this file can be easily emailed to the clinician for their evaluation of the impression.
In the last few years, many prosthodontists have conducted clinical research into the potential use of intraoral scanners for capturing complete edentulous soft tissue anatomy. This research looks very promising and will be the future method to capture this anatomy in a full digital workflow for complete denture prosthetics.
Accurate maxilla-mandibular records are essential to successful outcomes for complete denture prosthetics. The clinical relationship record phase does not change for conventional or digital workflows. Since these records clinically capture a joint (centric relation) or muscle (neuromuscular) position of the patient, they have to be scanned then registered with digital file of edentulous or terminal dentate arch (Figure 6 through Figure 8). Baseplates can be made conventionally with visible light cure (VLC) composite materials, vacuum form baseplate material, auto-polymerizing PMMA acrylic resin material, and processed base heat-cured material.
To date, the options for achieving accurate records for conventional, digital, or integrated workflows are duplicate dentures with check bite, wax occlusal rim, and central bearing devices. Accurate maxilla-mandibular relationship records are dependent upon a stable and retentive baseplate.
The main differences between conventional and digital tooth arrangement are the tools—a computer mouse (Figure 9 through Figure 20) versus heated instruments and wax. With conventional tooth arrangements or set-ups, the teeth are contoured then set individually in their proper positions (Figure 21). It can be a very tedious process to position each tooth properly according to the record, then secure it in place with wax.
With a digital tooth arrangement the mold selection, set-up and gingival base contour is created by the designer's mouse tool using CAE algorithms to control and assist in CAD process on monitor. The anteriors are set to reference record; then the posteriors are set at once to the reference record as well.
The huge advantage here is the ability to visualize the tooth arrangement within a transparency of record or reference data. When designing immediate dentures, the existing terminal dentition is used as a reference. Depending on the worn or broken-down dentition, each tooth can be scaled back to its full contour for a natural biocopy, an immediate transitional digital denture.
This phase of the denture workflow is where the different processes become evident. For conventional dentures, the most common processing method is either compression, injection or pour; for digital, it's either a subtractive/milling (Figure 21) or additive/printing process. The main difference between conventional and digital processing is elimination of variables that could create errors during the polymerization process of conventionally processed dentures (Figure 22 to Figure 24). These errors can cause porosity or increased vertical dimension of occlusion; the dentures must then be repaired or remounted to be equilibrated back to proper cusp-to-fossa ratio and incisal pin contact. With a digitally processed denture using subtractive or additive CAM methods, the occlusion is created and maintained in the design CAE process while the fit or intaglio to tissue surface is created at a 1:1 ratio, thus eliminating all variables of possible distortion that can occur during conventional polymerization process.
The finishing and polishing processes are the same in conventional or digital workflow, except with the latter only minimal contouring on the external surface is necessary. This is because the thickness and contours were controlled and established in the design phase (Figure 25).
When universities adopt digital workflows in curricula for dentists, denturists, and prosthodontists, more digitally educated professionals in prosthetic dentistry will be seeking digital workflow processes for their edentulous treatment solutions. It's simple math: the more clinicians educated in digital workflows, the greater the demand for digital prosthetics. As the number of educated and experienced dental technicians decreases, this will have subsequent affect on the demand for high-tech solutions. Clinical studies have shown digital workflows are more predictive versus reactive conventional linear workflows. This digital predictability creates better communication and collaboration within the prosthetic team while providing alternative treatment solutions for a compromised edentulous patient.
The author thanks Ingeborg De Kok, DDS, and Wendy AuClair Clark, DDS, for the clinical photos; the Dentsply Sirona Digital Dentures Engineered by AvaDent team for the design files; and Yulia Gafurov, CDT, for the conventional workflow photos.
About the Author
Robert Kreyer, CDT
1. Pound E, Murrell GA. An introduction to denture simplification. Journal of Prosthetic Dentistry. 1971; 26(6): 570-580. doi: 10.1016/0022-3913(71)90081-3