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Inside Dental Technology
October 2018
Volume 9, Issue 10
Peer-Reviewed

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.

Denture Diagnostics

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.

Impressions

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.

Records

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.

Tooth Arrangement

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.

Processing

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).

Conclusion

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.

Acknowledgements

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
Dentgnostix
Danville, California
Dentgnostix.com

Reference

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

Fig 1. For conventional, digital, or integrated workflows, a border-molded impression is still the optimal solution for capturing soft tissue anatomy within the denture space.

Figure 1

Fig 2. The duplicate denture technique with a wash impression captures soft tissue anatomy while providing an excellent reference for setting teeth conventionally or digitally.

Figure 2

Fig 3. For a digital workflow, the impression is scanned to create a design file.

Figure 3

Fig 4. After scanning, the impressions are converted to an STL file ready for digital denture design.

Figure 4

Fig 5. After scanning, the impressions are converted to an STL file ready for digital denture design.

Figure 5

Fig 6. With conventional workflow, the occlusal rim records and master casts are mounted on a dental articulator for designing maxillary and mandibular tooth arrangement and occlusal scheme.

Figure 6

Fig 7. With conventional workflow, the occlusal rim records and master casts are mounted on a dental articulator for designing maxillary and mandibular tooth arrangement and occlusal scheme.

Figure 7

Fig 8. With a conventional workflow, you can visualize the interresidual or prosthetic space from the facial, buccal, posterior or lingual, and occlusal views. The digital workflow allows visualization in perspectives that we could never see before. We can now look through the superior or inferior of articulator and model base to see the relationship of ridge, intaglio, and occlusion.

Figure 8

Fig 9. In the digital workflow, the baseplates and occlusal rims with records are scanned, creating a reference record for tooth arrangement. The teeth are then set with a transparent overlay of wax occlusal rim record for verification of tooth placement.

Figure 9

Fig 10. In the digital workflow, the baseplates and occlusal rims with records are scanned, creating a reference record for tooth arrangement. The teeth are then set with a transparent overlay of wax occlusal rim record for verification of tooth placement.

Figure 10

Fig 11. In the digital workflow, anterior and posterior teeth can be analyzed utilizing a reference grid for measuring facial surface of teeth to incisive papillae. The smile line, midline, incisal edge position, and buccal corridor are also analyzed with a 1-mm grid overlay.

Figure 11

Fig 12. In the digital workflow, anterior and posterior teeth can be analyzed utilizing a reference grid for measuring facial surface of teeth to incisive papillae. The smile line, midline, incisal edge position, and buccal corridor are also analyzed with a 1-mm grid overlay.

Figure 12

Fig 13. With a digital design workflow, the inter-arch ridge relationship can be analyzed from a facial/labial and posterior perspective while manipulating the size and position with a mouse.

Figure 13

Fig 14. With a digital design workflow, the inter-arch ridge relationship can be analyzed from a facial/labial and posterior perspective while manipulating the size and position with a mouse.

Figure 14

Fig 15. After the ridge is analyzed denture teeth are digitally arranged according to reference record as in Figure 10. With a digital workflow all the anterior teeth are set at once followed by all posteriors on the arch. Tooth arrangement and occlusion can be viewed in all possible perspectives in relation to residual ridges.

Figure 15

Fig 16. After the ridge is analyzed denture teeth are digitally arranged according to reference record as in Figure 10. With a digital workflow all the anterior teeth are set at once followed by all posteriors on the arch. Tooth arrangement and occlusion can be viewed in all possible perspectives in relation to residual ridges.

Figure 16

Fig 17. After the ridge is analyzed denture teeth are digitally arranged according to reference record as in Figure 10. With a digital workflow all the anterior teeth are set at once followed by all posteriors on the arch. Tooth arrangement and occlusion can be viewed in all possible perspectives in relation to residual ridges.

Figure 17

Fig 18. With transparency overlays both maxillary and mandibular tooth arrangements can be viewed from a superior or inferior perspective showing ridge, teeth, and centric occlusion.

Figure 18

Fig 19. The completed digital design of teeth and gingival base is viewed from the facial perspective.

Figure 19

Fig 20. For a try-in with a digital or integrated workflow, a milled functional Bouma try-in was made to evaluate fit, function, and esthetics. This functional Bouma try-in enables the patient to wear it at home for a personal evaluation of speaking, eating, and smiling. With a conventional workflow this functional try-in cannot be done since the teeth are set in wax.

Figure 20

Fig 21. After the digital functional try-in is approved, the design file moves to the manufacturing process of milling.

Figure 21

Fig 22. With a conventional workflow, after try-in the waxed denture arrangement is prepared for final waxing and investing for conventional compression processing. Conventional processing methods include compression, pour, microwave, injection, and continuous injection. Shown is compression because the majority of dentures in North America are compression processed using a manual, hydraulic, or pneumatic press to close flask.

Figure 22

Fig 23. With a conventional workflow, after try-in the waxed denture arrangement is prepared for final waxing and investing for conventional compression processing. Conventional processing methods include compression, pour, microwave, injection, and continuous injection. Shown is compression because the majority of dentures in North America are compression processed using a manual, hydraulic, or pneumatic press to close flask.

Figure 23

Fig 24. With a conventional workflow, after try-in the waxed denture arrangement is prepared for final waxing and investing for conventional compression processing. Conventional processing methods include compression, pour, microwave, injection, and continuous injection. Shown is compression because the majority of dentures in North America are compression processed using a manual, hydraulic, or pneumatic press to close flask.

Figure 24

Fig 25. With a conventional, digital or integrated workflow the finishing and polishing process remains the same. There might be more or less finishing and polishing depending on processing technique although the eyes and hands of a technician make detailed finishing touches on the complete denture at the end of all workflows.

Figure 25

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