Teeth whitening is a procedure that uses peroxide-based agents to lighten discoloration caused by coffee, tea, smoking, and aging. In-office whitening uses high-concentration solutions and can lighten teeth by several shades in a single session. However, discoloration in teeth that have undergone root canal treatment or in dental restorations may not be resolved by whitening. This information is for reference only and does not constitute a diagnosis; a consultation with a dentist is required.
[Source] Overview of Cosmetic Dentistry https://www.westchasesmilesinstitute.com/comprehensive-guide-to-cosmetic-dentistry/