What won't whiten
Crowns, veneers, bonding, tetracycline bands, one dark tooth, white spots, brown fluorosis, receded gums — and why they become the dark spot.
For about one in four people, peroxide won't get them where they want to go. Not because the product is bad — because of what's in their mouth.
Six things peroxide can't fix
Crowns, veneers, bonding, fillings. Porcelain and composite don't bleach; your teeth get lighter and the work stays put. Tetracycline bands. Gray or blue-gray stripes from childhood antibiotics — months of trays might lighten a little, rarely to white. One dark tooth. Usually an old hit and a dead nerve; outside bleaching does almost nothing, and it needs a dentist. White spots. Chalky patches from fluorosis or braces — whitening makes them more visible, not less. Brown fluorosis, mottling. Some brown responds; the pitted kind doesn't. Receded gums, exposed root. Root is dentin with no enamel: darker, doesn't bleach well, and peroxide on it hurts.
The mirror test
Smile wide in good light. A tooth a different color from its neighbors? Gray or blue tones? White patches? Dark at the gumline? Whitening may still help — but the plan has to work around them, and you need a realistic end shade before you start.
Do this now
Take a photo. Window light, no flash, lips pulled back, teeth together. It's one of the three photos the team looks at.