Crest 3D Whitestrips Sensitive and Gentle 18 Treatments / 36 Strips You can get a brighter, whiter smile in just 18 days with Crest 3DWhitestrips Sensitive and Gentle 30 minute teeth whitening treatment. It's specially formulated for teeth sensitive to whitening and has been accepted by the American Dental Association which means it is safe and effective. Using the same enamel safe whitening ingredient as dentists, you can get noticeably whiter teeth, guaranteed. Plus, a comfortable no slip grip helps the whitening strips stay put, so you can talk and drink water while whitening you teeth. Simply apply for 30 minutes a day for 18 days. This pack includes 36 teeth whitening strips, 18 for your top teeth and 18 for your bottom teeth, to be used over the course of 18 days.