# Analysis of 3D-Printed Zirconia Implant Overdenture Bars
## 3 Results  
All AM zirconia bars were fitted (screwed) onto the working soft tissue model and assessed as clinically acceptable, based on the following findings.  
* No binding and no issues with seating onto the implants.
* No detectable tactile discrepancies between the implant and bar.
* Radiographs indicated no discernible gap between the implants and bar.
* All bars could be torqued to approximately 15 N-cm without any issues.  
The bars were assessed for stability and fit using finger pressure, direct vision, tactile assessment (using an explorer), macrophotography, radiography, and thermography (Figure 11) (a novel mobile application was developed to assess the fit using surface temperature variations).  
Figure 11: AM zirconia bar and model. Composite radiograph (**left**) and thermography imaging (**right**) to assess fit.  
Figure 10: Location and direction of force vectors on the bar for testing.  
The denture fit onto the AM implant bar with a soft tissue model was also assessed with similar criteria. The denture fit (Figure 12) all AM implant bars with proper uniform seating and appropriate retention. Fit was evaluated using a standard fit check spray. Thermography was also explored as a possible adjunct fit tool (Figure 12, right), where uniform surface temperature would signify proper fit, and higher temperatures would indicate tightness.  
Applied Technical Services (Marietta, GA, USA) performed flexural testing according to ASTM D6272-17e1, using the provided fixtures as a guide. Testing was performed at a speed of 3 mm/min. The results are illustrated below.  
The max load (kN) applied to the AM zirconia solid bars (Table 1) was compared to the max load (kN) applied to the AM zirconia lattice bars (Table 2). There was no statistically significant difference between the two (\(p\) = 0.578). As shown in Table 3, the flexural results indicate no statistically significant difference between the AM zirconia lattice and solid bar designs. The average maximum fracture load was 1.2240 kN for the solid bar and 1.1132 kN for the lattice bar (Figure 13). The corresponding stress values were 147 MPa and 143 MPa, respectively (\(p\) = 0.578).  
Finite element analysis revealed the distribution of maximum principal stress across the two zirconia bars under the simulated fracture load. The model was meshed using tetrahedral elements and subjected to boundary and loading conditions replicating an in vitro setup. The stress distribution map shows that most of the structure experienced low to moderate stress levels, predominantly in the range from 0 to 29 MPa, represented by shades of blue and green.  
Localized regions near the screw holes and connecting areas between implants exhibited increased stress concentrations, with maximum principal stress values reaching up to 147 MPa (indicated by red zones). These peak stresses are critical and indicate potential areas of mechanical failure or fracture initiation under high-load conditions.  
Overall, both bar designs demonstrated comparable stress distribution with limited high-stress concentrations, suggesting a mechanically stable performance under the given load and little influence of the design itself (Figure 14).