# Analysis of 3D-Printed Zirconia Implant Overdenture Bars
## 2 Materials and Methods  
A master model (Figure 1), consisting of a conventional mandibular milled implant bar fixed to a soft tissue edentulous mandibular model with four dental implants, was sourced from a commercial laboratory (Panthera Dental, Quebec City, QC, Canada). The bar was composed of commercial-grade titanium alloy and was utilized for the zirconia implant bars. The implants used were from the Nobel Biocare Replace Select 4.0 implant system (Kloten, Zurich, Switzerland). This in vitro study did not involve human participants or animal subjects and therefore did not require ethical clearance. The titanium milled bar was scanned with a commercial-grade laboratory scanner (Shining 3D, San Francisco, CA, USA). The digital implant bar was optimized using Fusion 360 software (Version v.2603.1.15) (Figure 2) (Autodesk, San Rafael, CA, USA). The STL file of the implant bar was electronically transferred, and additive manufactured/3D printed at the Lithoz Centre (Troy, NY, USA) using LithaCon 210 3Y zirconia. The solid bar was printed/manufactured twelve (12) times (Figure 3). Complementary to the 3D printing process, all bars underwent post-processing, which included:  
* Cleaning after printing and removal from the build platform. * Thermal processing via drying (preconditioning), debinding, and sintering. * Measurement, visual inspection, and photography. Figure 1: Soft tissue master model with conventional milled titanium alloy mandibular implant bar. Figure 3: 3D-printed or additive-manufactured zirconia solid dental implant bar on demonstration model without soft tissue. Figure 2: STL file of the dental implant bar. The digital file of the 3D-printed bar was then modified and optimized to incorporate a lattice structure (Figure 4), for the printing of five (5) lattice-structured implant bars. The inclination angle during printing was set to 0\({}^{\circ}\), positioning the bar parallel to the build platform. The inter-implant distances were set 7.8 mm anteriorly and 11.4 mm unilaterally, along with a cantilever length of 6.8 mm. The minimum bar height was established at 5 mm, while the lattice design incorporated a minimum solid wall thickness of 0.9 mm, aligning with the capabilities of the additive manufacturing system. The lattice structure was developed featuring a ridge-like arrangement of perpendicular struts. Both the wall thickness and the drainage hole diameter (0.75 mm) were constrained by the requirements for effective powder removal and structural integrity during the manufacturing process. The lattice bar (Figure 5) underwent the same post-processing as mentioned above before testing. The bars were fitted onto the master model, both with and without the simulated soft tissue (Figure 6), and were assessed using (1) standard prosthodonic objective assessments (visual inspection, stability, integrity, etc. ), (2) macrophotonography and (3) radiology, to assess whether the bar was clinically acceptable or unacceptable. Figure 4: Implant bar design with circular cross-section internal lattice pattern (Image provided by ADEISS Inc., London, ON, Canada). Figure 5: An AM mandibular zirconia lattice-structured bar. The bar and soft tissue model were forwarded to a commercial dental laboratory (Alien Milling Technologies, Glendale, CA, USA) for the design and fabrication of an overdenture (Figure 7). The denture was a monolithic, single, continuous, and simultaneous print of the teeth and denture base using TrueDent, a multi-material 3D-printed denture (Stratasys, Minnetonka, MN, USA). Thermal imaging was conducted using the FLIR One Pro thermal camera (Teledyne FLIR, Wilsonville, OR, USA), which connects via the FLIR OneFIT(tm) interface to an Android-based mobile device. The camera offers a thermal image resolution of 19,200 pixels, a  
Figure 6: An AM mandibular zirconia lattice-structured bar on a model with and without soft tissue. Figure 7: 3D-printed mandibular denture on AM zirconia lattice bar with soft tissue model.