3D fabrication workflow

Dr Les Kalman

Thu. 7. September 2023

save

Dental implants remain the gold standard for the replacement of one or more missing teeth.^1, 2 In an edentulous arch, rehabilitation with implants provides the patient a significant improvement in function, aesthetics and quality of life.³ Implant bars, where a bone-affixed bar supports and retains the denture instead of it resting on the patient’s soft tissue,⁴ are predictable and cost-effective options. Implant bars are fabricated through subtractive manufacturing, or milling,⁵ and delivered to patients through a complex clinical workflow.⁶ The milling process has numerous disadvantages in terms of cost, efficiency and environmental footprint.^7, 8

As metal additive manufacturing (AM) matures, it presents a novel opportunity for the fabrication of implant bars, offering a process that promises to reduce both the time and the cost,^{9, 10} ultimately improving treatment accessibility. Moreover, AM provides a more sustainable approach, specifically through a more conservative lattice-structured design, reducing dentistry’s environmental footprint.^{11, 12} This report explains the workflow developed for the fabrication of additively manufactured solid and lattice-structured titanium alloy dental implant overdenture bars

Methods and materials

Milled bar
A dental implant metal bar was sourced from Panthera Dental. This bar was part of a patient education model, consisting of the implant bar, a model of the patient’s lower jaw and the simulated soft tissue (Fig. 1). The implant bar was milled from medical-grade titanium alloy (Ti-6Al-4V) on a fully robotic CNC machine at an Industry 4.0 manufacturing facility. The bar was monobloc, having no welded areas or porosity, and had a very accurate and passive fit with the implants on the model. The STL file of the bar design was provided by Panthera Dental.

Design
The implant bar design file was reviewed by ADEISS to evaluate the design for AM. Review for AM determined that the design required modifications to incorporate through-holes of 2 mm in diameter for implant placement, and the overall implant bar structure needed to be thickened to account for AM post-processing where surface finishing was required.

Two implant bar designs were generated for AM; the first design was a solid structure to replicate a standard implant bar, and the second design incorporated an internal latticed pattern within the bar component. The lattice design was created using standard CAD software functions with circular cross-sectional geometry (Ansys Spaceclaim 3D modelling software, Ansys; Figs. 2 & 3). Additionally, for the lattice-designed bars, drainage holes of 0.75 mm in diameter were incorporated into the anterior walls, such that non-consolidated powder from the AM process could be cleaned from the samples in post-processing. The final designs for AM were confirmed to match the dimensions of a comparative milled bar sample.

Fig. 2: Implant bar model with internal lattice pattern. (Image courtesy of © ADEISS)

Figs. 3a–c: Implant bar design with circular cross-section internal lattice pattern. Frontal view (a). Top view (b). Cross-sectional view (c). (Image courtesy of © ADEISS)

Selective laser melting (3D printing) and post-processing
The designs for AM were prepared for printing in medical-grade titanium alloy (Ti-6Al-4V). Printing was done using selective laser melting technology with the Renishaw AM 400 system (Renishaw). The 3D printer utilises alloy powder within the range of 30–50 µm in diameter and a 400 W laser of 70 µm in diameter in a 250 × 250 × 250 mm build volume. Eighteen implant bars (12 solid and six internal lattices) were fabricated in a machine print time of 7 hours and 6 minutes.

After the printing process, the implant bars on the build plate were cleaned using compressed air. Air was cycled across the build plate and through drainage holes until no loose powder was expelled. After powder clearance, the implant bars were exposed to standard heat treatment in a vacuum furnace, removed from the build plate and their surfaces finished. All implant bars were processed to a polished mirror finish (< 1 µm R_a) using hand tooling (Fig. 4). The final processing step included cleaning of all the implant bars using ADEISS’s ultrasonic cleaning methods to remove any remaining alloy powder and polishing agents.

Discussion

The AM-fabricated implant bars were all evaluated to be clinically acceptable, based on the fit with the original patient model and subsequently the fit of a denture (Fig. 5). Based on the number of implant bars that can be fabricated on a single build plate and the total time of fabrication and cost, the AM fabrication workflow suggests meaningful advantages over conventional milling of implant bars. Further research is being conducted through four-point testing and will be released shortly.

Fig. 4: Final additively manufactured latticed-structured dental implant bar.

Fig. 5: Additively manufactured implant bar screwed to the dental implants supporting a complete denture.

Conclusion

The AM workflow for both solid and latticed-structured dental implant bars indicated that AM is a suitable, and perhaps a superior, fabrication workflow for implant bars. Further research and metrics are needed. Workflows that provide improved cost-savings, efficiency and sustainability should be explored, not only to improve the patient experience, but also to enhance the sustainability of the profession.

Acknowledgements

Panthera Dental in Canada provided the milled implant bars and models. All design, manufacturing and post-processing for AM were completed by ADEISS in Canada. Alien Milling Technologies in the US provided the Ivotion (Ivoclar) denture. This research was funded by an International Congress of Oral Implantologists’ Implant Dentistry Research and Education Foundation grant. Special thanks to Dr Yara Hosein for her superlative assistance.

Editorial note:

The list of references can be accessed here. This article originally appeared in Oral Health Magazine, and an edited version is provided here with permisssion from Newcom Media. It was also published in CAD/CAM―international magazine of dental laboratories vol. 14, issue 1/2023.