Discoloration can come from surface stain, changes within a tooth, aging, injury, medications, decay, or existing restorations. These causes do not respond the same way. The examination may identify cavities, gum inflammation, cracks, exposed root surfaces, sensitivity, or a restoration that should be addressed first.
The American Dental Association recommends a clinical examination before bleaching so contributing factors and patient-specific considerations can be identified. A single darkened tooth, unexplained pain, swelling, or rapid color change needs diagnosis rather than cosmetic treatment alone.