Material Properties of Sintered incorus TZI Restorations with Classic, Speed and Superspeed Programs

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1 Temperature/ C Material Properties of Sintered incorus TZI Restorations with Classic, Speed and Superspeed Programs Objective incoris TZI restorations can be sintered with the infire furnace programs Classic, Speed und Superspeed. The objective of this study was to establish the effect of the sinter programs used on the following product properties: structural strength, fracture toughness, sinter density, fit and grain size. Sinter Programs Classic Speed Super Speed Time/mins Fig. 1 Sinter programs Classic, Speed und Superspeed Method The flexural strength was determined according to ISO 6872 as biaxial flexural strength. The examination for cracks in the restorations after sintering was carried out using a fluorescent penetrant dye. The density of the sintered restorations was determined using an analytical balance according to the Archimedes principle. The determination of the flexural strength and particle size was carried out on the sintered restorations (Classic and Speed Sintering: 6-unit bridges. Superspeed sintering: crowns(36)). The bridge crowns and connectors were sawn after sintering with a diamond cutting disc, the surfaces polished, thermally etched and then three Vickers indentations loaded on the polished surfaces. These Vickers indentations determine the fracture strength according to the Anstis method. The microstructure and the grain size were determined by SEM with three images per sample / restoration. The analysis of both the fracture toughness and grain size were carried out at the Fraunhofer Institute for Mechanics of Materials IWM. Fracture toughness is a parameter that defines the resistance of the material against unstable crack formation; particularly high values are desirable. ISO stipulates grain size 0.4 µm.

2 Results Table 1: Strength, crack degradation, sinter density and fit Properties Classic Speed Superspeed Biaxial flexural strength/ 1121 ± ± ± 135 MPa as per ISO 6872 Strength measurement lowest value/mpa Sinter density/ g cm Cracks None None None Fit Okay Okay Okay Using these three different sintering programs no significant difference between the Classic and Speed program was determined. The flexural strength with Superspeed sintering is somewhat lower, however, the lowest resistance value is slightly larger than the other sintering programs with 926 MPa. The different sintering procedures demonstrate in each case a sintered density of 6.07 g cm -3. Cracks due to the high thermo-mechanical load on the ceramic during the sintering process could not be detected using a microscope and fluorescent penetrant dye. The restoration fits of all 3 sinter programs were in order. Fracture toughness K IC The measured fracture toughness values are shown in Table 2. Table 2: Fracture toughness K IC /MPa m Sinter Classic Speed Superspeed Sample Crown Connector Crown Connector Crown ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.11 The fracture toughness of the Classic program sintered restorations are in the range 2.99 ± 0.05 to 3.24 ± 0.06 MPa m, for Speed sintering 2.81 ± 0.18 to 3.25 ± 0.04 MPa m and for Superspeed 3.22 ± 0.17 to 3.30 ± 0.11 MPa m. A significant difference between the values of the different sinter variants was not observed. Only the scattering of the SuperSpeed values is slightly greater.

3 K Ic /MPA m 3,5 K Ic Classic - Speed - Superspeed Sintering 3,4 3,3 3,2 3,1 3 2,9 2,8 2,7 2,6 P2326 P2328 P2330 P235-8 P242-6 P P P P Sample Kronen/Brückenkronen Verbinder Fig.1 Fracture toughness K IC Grain size/µm und microstructure The grain size measurement values of the ZrO2- Crystallites are shown in Table 3 Table 3: Grain size/µm Sinter Classic Speed Superspeed Sample Crown Connector Crown Connector Crown ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.14 The grain size of the Classic program sintered restorations are in the range 0.,34 ±0.15 to 0.37 ± 0.18 µm, for Speed sintering 0.27 ± 0.17 to 0.29 ± 0.13 µm and for Superspeed 0.31 ± 0.14 to 3.32 ± 0.14 µm. A significant difference between the values of the different sinter variants was not observed.

4 Grain size/µm Grain size - Classic - Speed - Superspeed Sinterung 0,6 0,5 0,4 0,3 0,2 0,1 0 Kronen/Brückenkronen Verbinder Probe Fig. 2: Grain size in µm for the 3 different sinter alternatives Fig. 3: Bridge crown microstructure images on 3 positions after Classic sintering

5 Fig. 4: Bridge crown microstructure images on 3 positions after Speed sintering Fig. 5: Crown microstructure images on 3 positions after Superspeed sintering Conclusion: The present study shows no degradation of material properties observed for both Speed and Superspeed in comparison to Classic sintering.