I have some at home, must begin using it again. Very cheap and effective
Haven't tried over-the-counter teeth whitening products. I get mine from the dentist. -Had the formed trays made by the dentist too....these make all the difference. It cost about $300 initially, but the whitening gel is only $10. I whiten them once a year or so if they become stained from coffee, tea and wine.
I think a weak solution of peroxide and baking powder works pretty well. It can't be any harder on the enamel than that grit stuff the hygienist uses when she polishes the teeth after scraping them. Because I am a night-time mouth breather, I get my teeth cleaned by the hygienist twice a year.
Even though I am a geezer, I still have thirty teeth, including all four wisdom teeth. My first molars were pulled when I was a kid with buck teeth and the orthodontist decided my mouth wasn't big enough to accommodate all my upper teeth. Yet some folks still tell me I have a big mouth! LOL.