Best for: Maintenance after an in-office whitening treatment.
Does it work? Yes. Because the trays are made specifically to fit your mouth, the peroxide spreads evenly on teeth. But beware of overbleaching: Peroxide can dissolve the calcium in tooth enamel (the outer layer), which exposes the nerves, resulting in sensitivity. Calcium depletion can also cause decay, says Fox. Though teeth can be remineralized with a paste or a fluoride treatment, you shouldn't wear the trays more than four to six times per year.
Cost: $400 to $800.