What is the objective of vital tooth bleaching with CARBAMIDE PEROXIDE?

Correct answer: B. Oxidative breakdown of pigmented organic molecules within the tooth structure

• A. Acid dissolution of enamel is what happens in EROSION — it damages the tooth and does not whiten it.
• B. CORRECT. Carbamide peroxide dissociates into HYDROGEN PEROXIDE and urea; roughly 10% carbamide peroxide yields about 3.5% hydrogen peroxide. The hydrogen peroxide generates free radicals that DIFFUSE through enamel into dentine and OXIDISE the large, conjugated, pigmented organic molecules — chromophores — held there, cleaving them into smaller, less light-absorbing fragments. The result is a genuine change in the INTRINSIC colour of the tooth, not merely surface cleaning.
• C. Bleaching does not add anything to the tooth. Adding an opaque layer describes an opaquer or a micro-abrasion-plus-resin-infiltration technique.
• D. Mechanical abrasion is how whitening TOOTHPASTES work on extrinsic stain. It cannot alter intrinsic colour.

Note: Carbamide peroxide is slower-releasing than hydrogen peroxide, which is why it suits overnight tray use: 10% carbamide peroxide worn 2–8 hours nightly for 2 weeks is the classic protocol. The urea component raises pH and is thought to reduce the sensitivity that is the commonest side effect, along with transient gingival irritation.