Groups N Mean (SD) P-value Tukey's post hoc
pairwise comparison
of ∆E
Group Significancea
Control 20 4.14 (0.98) 0.00;
df = 3 		PTFE 0.00
Ti 0.00
Zn 0.00
PTFE 20 2.23 (0.69) Ti 0.01
Zn 0.89
Ti 20 3.09 (0.95) Zn 0.08
Zn 20 2.43(0.82) -

aSignificant at the level P < 0.05 (Tuckey's post hoc test).
N = number; SD = standard deviation; PTFE = polytetrafuoroethylene.