Variable   Material   Bleaching agents   Mean ΔE   SD   Regression analysis for materials   Regression analysis for bleach agents
After first bleach  Durafil VS  Beyond  0.66  0.22  0.496  0.519
Luma  0.82  0.17
Opal XB  0.73  0.14
TPH3  Beyond  0.6  0.16
Luma  0.54  0.26
Opal XB  0.84  0.36
After staining  Durafil VS  Beyond  (–)4.44  1.52  0.001*  0.587
Luma  (–)3.43  0.55
Opal XB  (–)4.06  1.49
TPH3  Beyond  (–)2.12  0.33
Luma  (–)2.02  0.34
Opal XB  (–)1.68  0.49
After second bleach  Durafil VS  Beyond  0.91  0.21  0.035*  0.114
Luma  1.55  0.52
Opal XB  3.71  1.8
TPH3  Beyond  1.31  0.49
Luma  1.49  0.35
Opal XB  0.64  0.26
Between staining and second bleach   Beyond  4.16  1.09  <0.001*  0.002*