Bleaching

Definition

Bleaching is chemically lightening tooth color with peroxide compounds. The active agent is ultimately hydrogen peroxide, whether used directly or produced by the breakdown of carbamide peroxide (10% carbamide peroxide is roughly equivalent to 3.5% hydrogen peroxide). Peroxide penetrates the enamel and dentin, and the free radicals it generates oxidize pigment molecules — which have conjugated double-bond structures — breaking them into smaller fragments; these fragments absorb less light, so the tooth appears lighter. There are three main forms of application: home bleaching with a tray at low concentration, in-office bleaching at high concentration, and internal bleaching (walking bleach) for a discolored, endodontically treated tooth.

Concept Boundary & Misconceptions

A common assumption is that in-office bleaching, being stronger, gives a better and more stable result. Comparisons show the main difference is in speed, not the final result; the home method reaches the same level of lightening given more time, and often has better stability. For this reason, many protocols combine in-office bleaching as a fast start with home bleaching as the continuation of treatment.

The second misconception is the role of light and laser activation. Evidence shows light activation produces no clinically meaningful difference in the final result, and instead raises pulp temperature and sensitivity severity. What actually changes the color is peroxide concentration and contact time.

The third misconception concerns damage to enamel. Surface changes and a temporary reduction in microhardness are observed in enamel, but it remineralizes with saliva, and in controlled protocols we have no evidence of clinical weakening of enamel. There is, however, one real and important effect: residual peroxide inhibits resin polymerization and significantly reduces bond strength. This is why bonding immediately after bleaching is a mistake, and one should wait about two weeks.

And one last point that must always be told to the patient: restorations don't bleach. Composite, ceramic, and cement keep their color, and once the natural teeth lighten, they look mismatched. Tetracycline discolorations also respond slowly and incompletely.

Role in Clinical Decision-Making

Bleaching is the first and least invasive step on the ladder of esthetic treatment, and its place in the treatment sequence is what matters, not merely whether it's done at all. The right decision is to bleach before selecting the shade for any anterior restoration, wait two weeks for the color to stabilize and the peroxide's effect on bonding to clear, and only then take the final shade. Reversing this sequence condemns the patient to replacing the anterior restoration later.

Above all, the cause of the discoloration must first be established: extrinsic, intrinsic, or related to a non-vital tooth. Bleaching a color whose true nature hasn't been correctly diagnosed is simply an esthetic gamble, not a clinical decision.