Fracture load of machined Y-TZP zirconia fixed-dental-prosthesis frameworks, fabricated with different CAD/CAM systems

Abstract

Objective: The purpose of this study was to test yttria tetragonal stabilized zirconia (Y-TZP zirconia) frameworks machined using different CAD- and CAD/CAM-systems and determine whether the type of the zirconia and/or the type of the fabrication has an influence on the fracture load. The null-hypothesis was that no influence on the fracture load of the frameworks of zirconia fixed-partial-denture frameworks should be found. Methods: Two control and nine test groups allowed us to investigate the difference between densely sintered vs. pre-sintered zirconia, colored vs. non-colored, milled vs. ground, with or without water cooling. All frameworks in each group were fabricated by copying the shape of one master-framework. The fracture load of this identically shaped three-unit frameworks with 6mm2 interdental cross-sections was determined using a load to fracture test in a universal testing machine. Load data was analyzed using Anova Scheffe Alpha (.05) Results: Colored and wet-milled frameworks from hipped Y-TZP zirconia revealed the highest fracture load (2183 ± 451 N) and were significantly higher compared to all other groups. Neither the type of machining (production system, dry/wet milling, milling with cutters/diamond burrs) nor the mode of the coloring clearly influenced the fracture load. Regarding the dimensions of the frameworks prominent differences of the shapes and sizes of the frameworks machined with the different production systems were noticed. Conclusion: No clear conclusion can be drawn due to the differences of the investigated frameworks. Despite the high efforts to duplicate the shape of a master-framework none of the CAM- and CAD/CAM-systems was able to copy the master framework to full detail. A standardized production of the frameworks was not ensured. Further studies testing the fracture load of more standardized specimen are necessary