Table 2. Means and standard deviations of shear bond strength (MPa) of sandblasted surfaces of zirconia ceramic and cobalt-chromium (Co-Cr) alloy with and without ultrasonic cleaning.

Group	Mean	SD
Zirconia ceramic with ultrasonic cleaning	9.67 a	(3.11)
Zirconia ceramic without ultrasonic cleaing	13.11 a	(3.37)
Co-Cr alloy with ultrasonic cleaning	9.80 b	(5.19)
Co-Cr alloy without ultrasonic cleaning	13.60 b	(5.45)

n = 20, Statistical analysis: Mann-Whitney rank Sum test. Mean values represented with same superscript lowercase letters shows significant difference