Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Hurt my teeth and gums

These white strips had hurt my teeth and made my gums white. The trays also weren't very well fitting. I discontinued using them after 3 uses. After those 3 uses I really didn't see a noticeable change in the color of my teeth either. I think in the future I will look into getting them professionally whitened and lay off of the coffee and soda.