2). All steps were carried out by same technician with experience in ceramometal restorations. Each specimen was prepared in similar manner before porcelain application to achieve uniform surfaces; this was accomplished by using the sandblast in 25 μm ferric aluminum oxide powder on the metal alloy followed by exposure to air steam for 10 s. The AZD8055 in vitro B parts were used as holders for opaque porcelain; where the opaque porcelain was applied in five layers to fill each sample using Size #1 porcelain brush. Excess porcelain was removed with No. #11 sharp blade and sable brush. Specimens were allowed to air dry for minimum of 5 min before firing. Opaque porcelain was fired according to the manufacturer’s instructions for each porcelain system in both forms. The final thickness of opaque porcelain was maintained at 1.5 mm for all samples. All specimens were stored in water at 37 °C for 48 h before testing. A self-aligning fixture was fabricated for the Instron Universal testing machine to provide a repeatable method for introducing shear stress at the interface between the metal and the porcelain. This was also facilitated by designing the samples so that the interface was aligned at the midpoint relative to the thickness of each sample. Each test sample was mounted at one end of the superior element of the Instron machine by means of a steel rod 4 mm in diameter. The other end of the sample was mounted in a similar manner to the lower element of the machine. The Instron machine was gradually loaded until failure occurred. A chart speed of 1 inch/min was selected with a crosshead speed of 0.01 inch/min. Gradual loading was performed until the load deflection curve of each sample showed a sudden deviation on the chart, indicating bond failure. Bond strength values were recorded and calculated in MPa. Data were then analyzed statistically with ANOVA and t-test for multiple comparisons (α = 0.05) using the SAS statistical program (Version 9.1.3, SAS Institute). Furthermore, all specimens were evaluated microscopically using scanning electron micrographs (SEMs) at ×l500 to investigate the mode of failure. The load deflection curves were used to compute the stress necessary to shear the ceramic–metal bond. Corresponding means and standard deviations of shear bond strength of the three porcelain materials, in both forms, are presented in Table 2. Also, Table 3 shows the two-way ANOVA of shear bond strength across opaque form and porcelain system. Both factors and the interaction had significant effect on shear bond strength (P < .05). Likewise, one way ANOVA showed that there is a significant effect of opaque form on the porcelain-metal shear bond strength (P < .05).