Eliminating Variables for Successful Denture Outcomes

A digital workflow for 3D printed monolithic dentures

Robert Kreyer, CDT

In removable prosthodontics, our goal is to exceed expectations while eliminating or controlling variables that could create problems during the final insertion of definitive dentures. If these variables are not understood, controlled, or eliminated, then clinically there will not be a successful outcome with the insertion of definitive dentures. In making complete denture prosthetics, clinical and technical variables include materials, procedures, techniques, or equipment that can change or affect the desired outcome.

Traditional or analog denture workflows are composed with many prosthetic procedures in which variables such as impression materials; gypsum for models; mounting and processing; and measuring, mixing, and polymerization of acrylic resin must be understood and tightly controlled. With digital denture workflows, many of these material and procedural variables have been eliminated. The variable that can affect desired outcomes with most additive manufactured (AM) or printed digital dentures is the bonding of teeth into the denture base tooth pockets during assembly of denture parts with a split-file workflow. In order to achieve predictable outcomes, this variable must be controlled or eliminated.

In this case report, a two-appointment 3D printed copy denture workflow will be discussed. The copy denture workflow uses an existing denture as reference for the design of the teeth and base. If a patient desires minimal changes to fit and function, then the patient's existing denture teeth, base, and relationship record (bite scan) are used in design as a reference. A trial denture or try-in is not necessary with a copy denture workflow. If design modifications are made to esthetics, fit, and function, then a reference denture workflow with a 3D printed trial denture would be advised instead to confirm desired esthetic expectations and relationship record (centric relation and occlusal vertical dimension [OVD]).

Clinical Report Data Collection

The 3D printed copy denture workflow starts with the clinician taking a wash impression to improve fit and stability of the existing dentures. In this case, the clinician used a light body vinyl polysiloxane (VPS) for the wash impression, scanned the intaglio and cameo surface of each denture, and took a bite scan in centric occlusion. Clinical care must be taken to ensure that dentures are not displaced during the wash impression, and that the OVD is not increased due to the viscosity of the impression material.

The optimal clinical technique for wash impressions is to use a tissue conditioner material, capturing a functional impression over a 24- to 48-hour period. After the patient has functioned with tissue conditioner for a few days, the fit and border adaptation can be evaluated by the clinician. The dentures are then scanned for clinical data collection and design analysis (Figure 1).

Technical Process

Three STL files of the scans (upper/lower denture and bite) were exported to the laboratory for data and design analysis (Figure 2 and Figure 3). The prosthetic design technician conducted a data analysis, confirming that all necessary clinical data was collected before placing the files into the design portal. Design data was analyzed for proper registration (Figure 4) by referencing existing dentures and soft tissue anatomical landmarks. To improve function and stability, the plane of occlusion was established at two-thirds height of the retromolar pad, and mandibular posteriors were set according to Pound's triangle (Figure 4 through Figure 7).

The base was then built with tooth pockets set at a zero-degree offset. The manifold relationship between teeth and pockets created a precision monolithic design of base and teeth. Since the full arch of teeth was placed into base pockets using software, variables that could affect functional occlusion, such as manually bonding teeth to base, were eliminated (Figure 8).

Denture design files were then exported into CAD software (GrabCAD, Stratasys) for nesting onto a circular print tray of a polyjet 3D printer (J5, Stratasys) (Figure 9). After the print cycle, the printed dentures (TrueDent, Stratasys) were removed with support material encapsulating the intaglio and cameo surfaces of the teeth and base (Figure 10 through Figure 13). This unique support structure design created a high-fidelity fit and function while eliminating variables of distortion due to assembly of parts during the split-file printing and bonding process.

A scan of the printed dentures and comparison of the scan to the design using color coding to indicate the level of fidelity (Figure 14 through Figure 17) demonstrated the high dimensional data accuracy of the polyjet printing. Because of this, the traditional finishing process was able to be eliminated. The printed monolithic teeth and base should not be modified since this will create a finished denture that is different than the design file. If the patient desires another set of dentures from the same design file, then denture modification during finishing will prevent duplication of the original design. The dentures are printed to replicate the design file, thus eliminating finishing and going straight to polishing (Figure 18).

Clinical Assessment of Insertion

The case was inserted at the clinician's office (Figure 19 and Figure 20). The clinician in this case had decades of experience in complete denture prosthetics and extensive clinical knowledge in both analog and digitally fabricated dentures.

The clinician stated that, as with anything new, he was initially skeptical about the monolithic 3D printed denture, but that he was pleasantly surprised. He appreciated that printing the teeth and base in the same material without bonding made the denture much stronger and more durable than traditional printed dentures. He also complimented the excellent esthetics, stating that the teeth were vibrant and lifelike, and the base material was realistic and natural-looking. The fit of the denture was also excellent, with superior initial retention. The patient reported instant comfort, and no adjustments were needed (Figure 21 and Figure 22).

Overall, the clinician was very impressed with the 3D printed monolithic denture. It is a high-quality option that offers several advantages over traditional printed dentures.

Conclusion

The clinical insertion of the denture was found to have superior retention and stability. Function was accurate with no adjustments to occlusion in excursive movements. Prosthetic professionals desire workflows that improve efficiency and predictability with consistently successful outcomes. By understanding and eliminating prosthetic variables, these desires will become reality. In searching for an optimal digital denture product, consider how high-dimensional data and high fidelity combine in additive manufacturing to create a denture with superior fit and function.

Acknowledgement

The author acknowledges the clinician on this case, Charles Tatlock, DDS, MPH, a dentist at the Wagner Denture Group in Albuquerque, New Mexico, as well as Artisan Dental in Portland, Oregon, for collaboration on design and printing.