Yes, it should work in crevices. Strips generally cover the surface of the teeth but don't get into crevices because it is a plastic strip. With our product it is liquid gel that will get into the cracks and nooks of the teeth.
Hello, We don't recommend sleeping with the whitening gel. As per our instructions, we recommend whitening for 30 minutes per day. For deeper/stubborn stains, you can do back to back whitening sessions (2x 30 minutes each), using fresh gel after the first 30 minutes.
Hello Did you check below the batteries and remove them? If so and still nothing, please contact us at the link below so we can assist https://amazon.com/gp/help/contact-seller/contact-seller.html?sellerID=A21MTO7LOB9Z6I&marketplaceID=ATVPDKIKX0DER&ref_=v_sp_contact_seller