Why pay for Professional teeth whitening treatments? Crest 3D White Whitestrips Professional Effects is just as effective. These whitestrips are formulated with the same enamel-safe ingredient dentists use. Apply once a day for 30 minutes. You'll start seeing a whiter smile after three days, with full results in 20. Pack: 24. Dimensions: 21"L x 4"H x 9"W.