Immediately following a whitening session, teeth undergo significant dehydration due to chemical reactions within the gel and the effect of the applied light sources; the enamel tissue, having lost water, reflects more light, making the tooth appear much whiter and more opaque than it was on the first day. Within 48 to 72 hours following the procedure, the enamel layer rehydrates by reabsorbing ions and water from saliva, and during this time, the tooth’s color returns to its true shade, i.e., darkening by 1-2 shades; this is called the rebound effect. Furthermore, during this initial 48-hour period, the organic matrix of the enamel is extremely permeable to external coloring pigments, and if the patient does not adhere to “white diet” rules, pigments seeping into the pores with saliva can lead to permanent color reversal.
