Charcoal, whitening toothpaste and LED gadgets do not change the colour of dentine. Peroxide does — under supervision.
Enamel is translucent; the colour you see is mostly the dentine underneath. Surface stains from coffee and tobacco sit on the enamel and polish off. Real whitening means changing the dentine shade, and only peroxide chemistry does that.
Charcoal and 'whitening' pastes work by abrasion. They remove surface stain and, with daily use, enamel — and thinner enamel makes the yellow dentine show through more. The result is a tooth that looks darker after a year of scrubbing.
In-clinic whitening uses a higher concentration with the gums isolated behind a barrier, achieving several shades in 45 minutes. Home trays work more slowly at lower concentration and suit maintenance. Both are safe under supervision; unsupervised high-concentration gel is how people burn their gums.
Tetracycline staining, single dark root-treated teeth, and existing crowns or fillings will not lighten. Those need veneers, internal bleaching or replacement — which is why we whiten before matching any new restoration.
One to two years depending on coffee, tea, red wine and smoking, with a top-up session extending it.