Tooth structure in brief
A tooth has an outer layer of enamel - highly mineralized and semi-translucent - over a layer of dentin, which is naturally more yellow. The color you see is a mix of both, plus any stain that has accumulated on or within the enamel.
Extrinsic stains
Extrinsic stains sit on the outside of the enamel and come from pigmented food and drink (coffee, tea, red wine, curry), tobacco, and some mouthwashes. They typically respond well to abrasion (brushing, polishing) and to peroxide-based whitening.
Intrinsic discoloration
Intrinsic color changes come from inside the tooth - thinning enamel that reveals more dentin, developmental causes, trauma, some medications (e.g. tetracycline exposure during tooth formation), and aging. These do not respond to surface polishing and often respond less predictably to at-home whitening (ADA Council on Scientific Affairs; NIH/NIDCR guidance on tooth discoloration).
Why this matters for choosing a method
- Surface stain from coffee → toothpaste, strips, or trays are often enough.
- Intrinsic discoloration → professional treatment or cosmetic options (veneers, bonding) may be more effective.
- Existing crowns, veneers, and fillings will not change color and can end up mismatched after whitening.