I have used these strips several times and am very happy with them. I recently got another box and for some reason several of them have not stuck to my teeth had to throw them away without using. The first two I did not think to email but just had two more same things happened. I am not sure if it was just something wrong with this box. The lot of number is 303219 a. Exp date is 08/2022. Thank you Arlene Austin [protected]@yahoo.com