Comparison of Fractural Strength of Metal Ceramic Bonding Obtained by Microwave and Conventional Oven Heating.
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Objectives. The goal of this study was to evaluate the bond strength of porcelain fused to metal sintered in a microwave oven and compare it to that sintered in a conventional oven. Methods. High gold alloy (d.SIGN 91, Ivoclar Vivadent) was cast into 30 (25x3x0.5mm) strips following manufacturer’s directions. An 8x3x1 mm porcelain strip (d.SIGN, Ivoclar Vivadent) was centered on each of the metal strips and sintered as described below. The specimens were randomly divided into three groups (n=10). The first group (control) was degassed and sintered in a conventional oven. The second group was oxidized in a conventional oven and sintered in a microwave oven. The third group was oxidized and sintered in a microwave oven. All specimens were subjected to a three-point bending test at a crosshead speed of 1.5mm/min -1 until debonding occurred, using a universal testing machine. A precision measurements microphone was used to assist in ascertaining the point in time when the initial debond/crack occurred. Fractured specimens were carbon coated and examined with scanning electron microscope for fractographic analysis. Data were statistically analyzed using one way ANOVA and the Tukey HSD test was used for all pair wise multiple comparisons (α=.05) using statistical software SPSS 16.0. Results. The mean debonding strength values in MPa for each group were: 69.51 (SD 5.16) for the conventional oven process, 55.25 (SD 10.6) for combined conventional degassing and microwave sintering, and 61.16(SD 10.99) for microwave processing. Significant differences among the groups were detected by one-way ANOVA (p=0.008). Post-hoc analysis using Tukey test revealed significant differences between the conventional and the combined processes (p=0.006). No statistical differences were detected between the conventional and the microwave processes (p=0.132) or between microwave and the combined processes (p=0.348). Conclusions. The fractural strength of sintered porcelain fused to metal sintered with a microwave is comparable to that sintered in a conventional oven.