Dr. Ronald D. Perry, the director of the Gavel Center for Restorative Research at Tufts University School of Dental Medicine, said that over all, “the light doesn’t really do anything, but the marketing behind it is so powerful.”
Before any bleaching, even when it’s done at home, a dentist should check fillings and crowns, because, Dr. Perry said, applying peroxide to a restoration that is no longer perfectly sealed will be very sensitive.
In a 2014 review of tooth whitening studies, Clifton Carey, a professor at the University of Colorado School of Dental Medicine, warned that fillings that are designed to match the tooth’s color might get more yellow after even drugstore whiteners. Or, if teeth get whiter, and a filling doesn’t, it might stand out.
Not all staining is alike. It can be caused by external factors like wine, coffee, cola and smoking, and bleaching is effective against these. Aging is another culprit, as enamel wears down and the yellower dentin that lies beneath becomes visible. Bleaching does work on older teeth, too.
Unfortunately, it’s tricky to say how long the results of tooth whitening will last. A nightly merlot drinker with freshly lightened teeth may re-stain them in a month or two.
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