Table 5.  Means and standard deviation values for surface roughness for all subgroups of the two composites in shade A4.
Variable   Material   Bleach   Mean   SD   Regression analysis for materials   Regression analysis for bleach agents
After first bleach  Durafil VS  Control  106.7  2.1  <0.001*  0.039*
Beyond  107.2  2.4
Luma  109.2  2.1
Opal  114.3  2
TPH3  Control  100.5  5.3
Beyond  102.6  8.1
Luma  100.2  4.9
Opal  106.1  5.9
After second bleach  Durafil VS  Control  106.7  2.1  <0.001*  <0.001*
*:  Significant at P≤.05