All a scam, ive tried everything, ive tried brushing for a long time, short time, brush hard, brush soft, no brush just put it on one tooth and leave it for some time, and no difference in my teeth, if something, theyre more yellow. DONT BUY THIS, ALL A SCAM, also, 30 dollars for 30ml of this is unacceptable, costed me about 40 dollars additionally for shipping and toll. So 70 dollars, crazy.