Home whitening: concentration decides application time, not the final result

Home tray whitening has the strongest documentation among whitening techniques, and it is the one on which patients hold the least accurate expectations.

The active agent is peroxide, which releases free radicals capable of breaking down pigmented molecules within enamel and dentine. It removes nothing from the surface: it acts in depth.

Carbamide peroxide splits into hydrogen peroxide and urea at a constant ratio: ten per cent carbamide corresponds to roughly three and a half per cent hydrogen peroxide.

This gradual breakdown is what makes carbamide suitable for overnight use, because it continues releasing active agent for several hours.

Hydrogen peroxide acts faster and is exhausted sooner, making it the choice for daytime applications of thirty or sixty minutes.

The point that changes expectations is this: concentration determines how quickly the result is reached, not how white the tooth will become. Higher concentrations shorten treatment, they do not improve the endpoint.

It follows that starting from low concentrations is almost always sensible: one arrives at the same place with less sensitivity, which is the side effect that causes treatment to be abandoned.

The tray is built on a model with spacers on the buccal surfaces, creating a reservoir that holds gel where it is needed. A thermoformed tray without reservoirs distributes the product poorly.

The margin is trimmed just above the gingival line, without covering the gingiva. A tray that overlaps causes gingival irritation and concentrates gel where it serves no purpose.

Sensitivity during treatment is common and transient, and is managed without stopping: shortening applications, alternating days, using a potassium nitrate toothpaste in the preceding weeks.

Applying a desensitising gel in the same tray, alternating with the whitening agent, is the most effective strategy in patients reporting marked discomfort.

Colour relapse should be explained in advance: part of the result is lost over the following months, and a maintenance cycle of a few applications a year preserves it. A patient who does not know this concludes the treatment failed.

In summary: concentration governs timing rather than outcome, carbamide is for overnight and hydrogen peroxide for daytime, the tray needs reservoirs and must not touch the gingiva, and relapse should be explained beforehand alongside maintenance.