## **Core Concept**
The question pertains to the technique of home bleaching prescribed by a dentist, which involves the use of a bleaching agent, typically **hydrogen peroxide** or **carbamide peroxide**, in a custom-fitted tray to lighten tooth color.

## **Why the Correct Answer is Right**
The correct answer, **Night guard bleaching**, also known as **at-home bleaching** or **custom-fitted tray bleaching**, involves a dentist taking impressions of the patient's teeth to create a custom-fitted tray. This tray is then filled with a bleaching agent, usually **carbamide peroxide**, which breaks down into **hydrogen peroxide** and **urea**. The urea helps to stabilize the hydrogen peroxide, allowing for a more controlled and sustained release of the bleaching agent. This technique is popular for its convenience, allowing patients to bleach their teeth at home, and its effectiveness in achieving noticeable teeth whitening.

## **Why Each Wrong Option is Incorrect**
- **Option A: Walking bleach** - This technique involves the use of a bleaching agent inside a tooth that has undergone root canal therapy, not for at-home use on vital teeth.
- **Option B: Power bleaching** - This refers to in-office bleaching techniques that use high concentrations of hydrogen peroxide, often activated by a light source, and is not a method for at-home use.
- **Option D: Non-vital bleaching** - This technique is used for teeth that are no longer alive (non-vital), often involving a different approach than at-home bleaching.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for at-home bleaching, a custom-fitted tray is essential for even distribution of the bleaching agent and to minimize gum irritation. Patients are typically advised to wear the tray for a specified number of hours per day or overnight, as in the case of **night guard bleaching**.

## **Correct Answer:** . Night guard bleaching