Tooth Bleaching for Discolored Teeth: Techniques Explained

Tooth bleaching lightens discoloured teeth using peroxide-based gels. It does not add or remove tooth material — it breaks down the pigmented molecules (chromophores) trapped in enamel and dentine.

This topic matters because tooth whitening is one of the most requested cosmetic treatments worldwide, Students must know which stains respond and the correct concentrations for home and in-office techniques.

Key Concepts

• Chromophores: large molecules with alternating double bonds that appear as yellow, brown or grey stains; peroxide breaks them into smaller, colourless fragments.
• Carbamide peroxide: the agent used in dentist-supervised home bleaching, typically 10, 16 or 22 percent in custom-fitted trays worn for several hours or overnight.
• Hydrogen peroxide: the active bleaching agent itself, used directly at 25 to 40 percent for in-office power bleaching, applied by the dentist in 15 to 20 minute sessions.
• Conversion: 10 percent carbamide peroxide breaks down to release approximately 3.6 percent hydrogen peroxide plus urea — this is why a "10 percent" home gel is far milder than a "35 percent" in-office gel.
• Vital vs non-vital bleaching: vital bleaching whitens living teeth from outside; walking bleach whitens a root-treated tooth from inside the pulp chamber.

How It Works

1. For home bleaching, impressions are taken and thin custom trays are made; the patient places a small bead of carbamide peroxide gel in each tooth compartment and wears the tray as instructed.
2. Inside the tray, carbamide peroxide slowly releases hydrogen peroxide, which diffuses through the enamel into the dentine.
3. Peroxide releases free radicals that fragment chromophores into smaller colourless compounds — the tooth lightens over days to weeks.
4. For in-office bleaching, the dentist protects the gums with a barrier, applies high-concentration hydrogen peroxide gel directly, and may repeat the application two or three times in one visit for faster results.
5. For a dark non-vital tooth, a mixture of sodium perborate and water is sealed inside the emptied pulp chamber ("walking bleach") and changed weekly until the shade matches.

Worked Example

A home-bleaching tray for the upper teeth holds 0.5 mL of 10 percent carbamide peroxide gel per application. Calculate the mass of active hydrogen peroxide delivered.

1. 10 percent carbamide peroxide releases approximately 3.6 percent hydrogen peroxide by mass.
2. 0.5 mL of gel weighs approximately 0.5 g (the gel's density is close to that of water).
3. Mass of hydrogen peroxide = 3.6 percent of 0.5 g = 0.036 × 0.5 g = 0.018 g.
4. 0.018 g = 18 mg of hydrogen peroxide per tray application.

Common Misconceptions

• "Bleaching works on crowns, veneers and fillings too." Corrected: peroxide only lightens natural tooth structure. Restorations keep their original shade, so they may need replacement after bleaching to match the new tooth colour.
• "Whitening toothpastes bleach teeth the same way." Corrected: most whitening toothpastes only polish away surface stains with abrasives and cannot change the intrinsic shade.
• "Once bleached, teeth stay white forever." Corrected: teeth gradually re-stain from tea, coffee, tobacco and ageing. Touch-up treatments every 1 to 2 years maintain the result.

Real-World Applications

• Aesthetic dentistry: bleaching is the conservative first step in smile design, often done before veneers or bonding so restorations can be matched to the whitened shade.
• Single dark tooth: walking bleach rescues a discoloured root-canal-treated front tooth without needing a crown.

To recap, tooth bleaching lightens teeth by using peroxide to fragment stain molecules inside the enamel and dentine — 10 percent carbamide peroxide at home (about 3.6 percent active peroxide) or 25 to 40 percent hydrogen peroxide in the clinic. It works only on natural tooth structure, causes temporary sensitivity at most, and needs professional shade assessment first.