IADR Abstract Archives
Influence of Fabrication Settings on the Performance of Zirconia Crowns
Objectives: The aim of this in-vitro study was to investigate the influence of milling parameters on the durability of zirconia molar crowns during in-vitro aging-simulation and fracture force.
Methods: Identical molar zirconia crowns (IPS emax ZirCAD Prime, Ivoclar, FL; n=8 per group) were milled from a standard 98 mm disc employing different configurations (MCX5, Dentsply Sirona, USA; bur 0.5, 1.0 and 2.5) with different processing stage (soft, normal, fast; influence on process time and surface finish) and level of detail (very high bur 0.5, 1.0 and 2.5, high bur 1.0 and 2.5, low bur 2.5; selection of milling tools). All crowns were adhesively bonded on standardized resin-based composite molars. Artificial aging was performed with thermal cycling and mechanical loading (2x3000x5°C/55°C, 2 min, H2O dist., 1.2x106 force 50 N). Fracture forces were determined (v = 1 mm/min, Z010, Zwick, Germany). Statistics: Pearson-correlation, one-way ANOVA, Bonferroni post-hoc-tests (α=0.05).
Results: No crown failures occurred during TCML. The fracture forces ranged between 1551.1 +/- 225.0 N (soft/very high) and 2178.6 +/- 479.0N (soft/low). Significant (p<0.001) differences between groups were identified in ANOVA comparisons. No correlation was observed for fracture force and the processing stage (Pearson: 0.153/ p=0.199) or the level of detail (0.124/0.301). Tests showed intermediate subject effects for the level of detail (p=0.007) and the level of detail*processing stage (p=0.002). Significant differences (p=0.006) were identified between high and low level of detail.The failure pattern in the fracture test was similar for the tested systems and characterized by partial or complete fracture of the crown and partial loosening of the crown remnants from the tooth.
Conclusions: The fracture forces were only slightly influenced by the different machining parameters of the milling machine. A low level of detail in combination with a soft machining stage appears to be ideal for achieving the highest fracture forces. All zirconia crowns provided good in vitro performance and fracture values, which are required for long-term clinical use.
Methods: Identical molar zirconia crowns (IPS emax ZirCAD Prime, Ivoclar, FL; n=8 per group) were milled from a standard 98 mm disc employing different configurations (MCX5, Dentsply Sirona, USA; bur 0.5, 1.0 and 2.5) with different processing stage (soft, normal, fast; influence on process time and surface finish) and level of detail (very high bur 0.5, 1.0 and 2.5, high bur 1.0 and 2.5, low bur 2.5; selection of milling tools). All crowns were adhesively bonded on standardized resin-based composite molars. Artificial aging was performed with thermal cycling and mechanical loading (2x3000x5°C/55°C, 2 min, H2O dist., 1.2x106 force 50 N). Fracture forces were determined (v = 1 mm/min, Z010, Zwick, Germany). Statistics: Pearson-correlation, one-way ANOVA, Bonferroni post-hoc-tests (α=0.05).
Results: No crown failures occurred during TCML. The fracture forces ranged between 1551.1 +/- 225.0 N (soft/very high) and 2178.6 +/- 479.0N (soft/low). Significant (p<0.001) differences between groups were identified in ANOVA comparisons. No correlation was observed for fracture force and the processing stage (Pearson: 0.153/ p=0.199) or the level of detail (0.124/0.301). Tests showed intermediate subject effects for the level of detail (p=0.007) and the level of detail*processing stage (p=0.002). Significant differences (p=0.006) were identified between high and low level of detail.The failure pattern in the fracture test was similar for the tested systems and characterized by partial or complete fracture of the crown and partial loosening of the crown remnants from the tooth.
Conclusions: The fracture forces were only slightly influenced by the different machining parameters of the milling machine. A low level of detail in combination with a soft machining stage appears to be ideal for achieving the highest fracture forces. All zirconia crowns provided good in vitro performance and fracture values, which are required for long-term clinical use.