entist Supervised Tooth Whitening Dentist-supervised tooth whitening involves the controlled use of carbamide or hydrogen peroxide, tailored to a particular patient. Dentists may administer in-office treatments or at-home treatments. Before the tooth whitening treatment, most dentists clean the teeth, fill any cavities, and make sure the patient's gums are healthy. Most in-office systems use 15 to 35 percent hydrogen peroxide gels, sometimes coupled with a high intensity light to expedite the bleaching chemical reaction. (Some recent research has questioned the need and effectiveness of the light source used during in-office tooth whitening.) The in-office procedure involves the dentist gently cleaning your teeth with pumice and then putting a protective barrier on the gums. The dentist then places hydrogen peroxide paste on the teeth for several minutes, rinses it off, and usually reapplies it several times. The procedure can achieve about four to six shades of whitening after only one 40-minute treatment.