Fracture strength of secondary crown with different taper and thickness in zirconia double crown attachments

The objective of this study was to clarify the influences of zirconia materials, one-half taper angle, and thickness of the secondary crown on the fracture strength of the secondary crown. For the primary and secondary crowns, Y-TZP and Ce-TZP/Al2O3 were used, respectively. Samples were prepared at one-half taper angles of 2 degrees and 4 degrees, and a secondary crown thickness of 0.5 and 1.0 mm (n=8). Regarding the fracture strength, the secondary crown was restored on the primary crown, all specimens were loaded until fracture using a universal testing machine. The load value added at the time of secondary crown fracture was regarded as fracture strength. Based on the analysis of variance, the fracture strength of Ce-TZP/Al2O3 was significantly higher than that of Y-TZP with regard to the material and that at 1.0-mm thickness was significantly higher than that at 0.5-mm thickness, but the taper angle had no influence.