The route barely matters; the pacing does. Strips at 10% hydrogen peroxide, twice daily for two weeks, reach the same endpoint shade as 35% in-office gel in one or two visits. Pooled across nineteen trials, at-home and in-office came out even on both final whiteness and sensitivity ¹.

Carbamide peroxide is hydrogen peroxide on a delay. Overnight tray gels break down slowly, so a 10% carbamide tray and a 3% hydrogen strip land in similar places ². What scales with concentration is speed and the sensitivity along the way.

It fades. At six months, tray teeth are still clearly lighter but drifted back a fifth to a half of the way ³. Two touch-up nights twice a year holds the shade; skip that and you slide to baseline over one to two years.

Three routes work. Try the cheapest first, since the shade you land on is about the same either way.

If your teeth already zing with cold, ask for a desensitizing gel (potassium nitrate with fluoride) to wear in the tray first; it roughly halves the chance of sensitivity without slowing the whitening.

The arc runs slow, then obvious.

• Days one to three: nothing visible, maybe a faint cold-zing. This is where people quit too early.
• Week one: teeth look cleaner more than whiter. People who see you daily don't notice.
• Week two: photos look different, and someone who hasn't seen you in a month asks if you did something. This is where the shade crosses "perceptible" in the trials ¹.
• Year one on: with two touch-up nights twice a year, the week-two shade is the shade you still have at year five. Without them, a third faded by month six ³.

This buys you nothing for your energy, sleep, or lifespan. It's cosmetic, and it works.