Table 2: Experimental groups and the manufacturers and compositions of the whitening agents used.

Group	Whitening agent / Manufacturer	Composition	Treatment
OP38	Opalescence Boost PF 38% / Ultradent Products, South Jordan, UT, USA.	Hydrogen peroxide 38%, potassium nitrate and fluoride.	2 X 15 min/day, 1 session/week, for 3 weeks.
PO37	Pola Office 37.5% / SDI Limited, Bayswater, Victoria, Australia.	Hydrogen peroxide 37.5%, additives, glycerol, water and aromas.	30 min/day, 1 session/week, for 3 weeks.
CO (CONTROL)	-	-	Without treatment. (this group was used only for the IC test)