الفهرس 
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Abstract
In this study, ten patients with completely edentulous maxilla opposing mandibular class I Kennedy were selected from the outpatient clinic of the Removable Prosthodontic Department, Faculty of Dentistry, Ain Shams University.
For each patient, three upper single dentures were constructed. Each patient received the most retentive denture at the end of the study.
• group A: Conventional acrylic resin maxillary single dentures.
• group B: Maxillary single dentures reinforced with digitally designed and milled Cobalt chrome framework.
• group C: Maxillary single dentures reinforced with digitally designed and milled Zirconia framework.
Acrylic unreinforced dentures were constructed in a conventional manner. Impressions were poured with dental stone immediately to obtain study casts on which special trays were constructed using acrylic resin. Upper secondary impressions were made with rubber base impression material, lower secondary impressions were made after the necessary occlusal adjustments using alginate impression material, and final impressions were poured using extra hard stone.
The upper master cast was duplicated using a duplicating silicone mold, and the mold was poured using extra hard stone, to obtain four master casts, three master casts on which three maxillary dentures were constructed and the fourth was prepared to be duplicated for the epoxy resin casts construction with mucosa simulation to be mounted in the chewing simulator device.
The hard stone master cast was scanned by the Ds Mizar desktop scanner. Digital data in STL format was imported into the digital design software EXOCAD partial module and the framework was designed. The STL file of the designed framework was imported to 5 axis milling machine to be milled to both Cobalt chrome and Zirconia frameworks from Cobalt chrome and Zirconia blanks.
The frameworks were incorporated into the two maxillary dentures by conventional heat-curing PMMA acrylic resin, the resin was packed and processed in a conventional manner.
A metallic ring was attached to the polished surface of the denture bases at the position of the geometric center by self-cure acrylic resin. A digital force gauge was used to record the retention of the maxillary dentures.
All maxillary denture fitting surfaces were scanned using the DS Mizar desktop scanner, outputting an STL file. The STL file was imported to the Meshmixer software to flip the fitting surface of the denture base to resemble a cast surface then the Geomagic software was used to evaluate the adaptation of the upper denture bases on the scanned master cast by using surface-matching software.
The fourth maxillary master cast was prepared and duplicated using a duplicating silicone mold to have three identical polyurethane epoxy resin cast with soft tissue simulation for each patient to be used in the chewing simulator device,
For each patient, the maxillary dentures of the three groups were evaluated for retention and internal adaptation before and after dynamic fatigue loading applied with the chewing simulator device.
All data was collected and tabulated for statistical analysis.
Conclusion
Within the limitations of this study, it could be concluded that:
• After one year of simulation, maxillary dentures reinforced with CAD/CAM Zirconia framework are the best treatment option regarding retention and adaptation.
Recommendation
Further research is recommended to
1- Study the adaptation and retention of maxillary dentures reinforced with a selective laser melting (SLM) Co-Cr framework and compare it to our study.
2- Laboratory evaluation of maxillary dentures retention