What is the objective of tooth whitening with carbamide peroxide?

Carbamide peroxide (used in dentist-dispensed whitening systems, typically 10-22% concentration) breaks down into hydrogen peroxide and urea. Hydrogen peroxide (and its free radical byproducts) penetrates enamel and dentin and oxidizes large, dark-pigmented organic molecules into smaller, less pigmented compounds. This chemical reaction lightens both intrinsic stains (within enamel and dentin) and extrinsic stains. The process is not merely mechanical (abrasion). Common side effects include transient tooth sensitivity and gingival irritation. The whitening effect can last 1-3 years depending on diet and habits.