# Analysis of 3D-Printed Zirconia Implant Overdenture Bars
## 4 Discussion  
A workflow was developed to predictably fabricate zirconia dental implant overdenture bars through additive manufacturing (AM), which was the investigation's main aim. The trial-and-error aspect (print, post-process, assess) was challenging but necessary to formulate an appropriate algorithm for an accurate digital design, compensating for the bar's shrinkage from sintering and debinding. Solid bars and lattice-structured bars were both fabricated, indicating that complex geometries are possible with digital design and AM utilizing zirconia. Figure 14: Finite element analysis showing the distribution of maximum principal stress in the AM zirconia bars under simulated loading conditions. (**a**) The lattice bar design demonstrates localized stress concentrations near support regions with a slightly more diffuse distribution. (**b**) The solid bar shows similar stress localization, with peak stresses also occurring at support contact areas. Both designs exhibit fracture initiation correlating with these high-stress zones. Figure 13: Comparison of mean flexural strength between AM zirconia lattice and solid bars. The graph displays the average maximum fracture load (in kN) for each design. No statistically significant difference was found between the two groups (\(p=0.578\)). All AM bars were deemed clinically acceptable on the simulated patient model, as assessed by (1) standard objective prosthodonic assessments (visual inspection, stability, integrity, etc. ), (2) macrophotography, and (3) radiology. A novel thermography platform was also employed and indicated promise in determining fit based on surface temperature gradients. In Figures 11 and 12, the distal implants on the right side exhibited slightly higher temperatures during thermographic analysis. While this may reflect normal variability, one possible contributing factor could be manufacturing asymmetries during assembly, such as fitting, assembly sequence, or torque consistency of screw tightening. Although this hypothesis was not directly tested, it highlights the importance of standardizing these variables in future studies. Clinically acceptable misfit values for implant superstructures are generally considered to be less than 120 \(\upmu\)m [24]. Misfit within this range has been shown to maintain prosthetic stability and minimize biological complications [24]. Although precise quantification was not performed in this study, the observed adaptation of the AM zirconia bars was clinically acceptable based on visual assessment. The model and bar were scanned for the fabrication of a 3D-printed denture. The denture fit on all bars and models was clinically acceptable, as determined by similar prosthodonic assessments, photography, and radiology. Thermography was also employed and showed promise in aiding fit assessment between the bar and denture. Solid AM zirconia bars withstood an average maximum load of 1.2240 kN, which was higher than the AM zirconia lattice-structured bars, which withstood an average maximum load of 1.1132 kN, with a difference of 0.1108 kN. There was no statistical difference between the two groups (\(p=0.578\)). An ongoing pilot study led by the first author is currently exploring a similar project involving AM solid and lattice-structured titanium alloy implant bars. The solid titanium bars withstood an average maximum load of 5.715 kN. The bar fractures (failure) occurred in different locations but seemed to coincide with the location of the supports on the custom-fabricated fixtures (Figure 15). Future research may consider equal stress distribution fixtures or the incorporation of the soft tissue model for testing. The average weight of a solid bar (Table 4) was 8.03 g, while the average weight of the lattice-structured bar (Table 4) was 6.93 g. Lattice-structured bars weighed an average of 1.1 g less than solid bars.