Instruct: Classify Amazon reviews into positive or negative sentiment
Query: No difference

I have now bleached my teeth almost 10 times with this product and have noticed no difference. I'm keeping it on for 1.5-2hrs at a time. I'm not sure what's going on but everytime I remove the trays and look at my teeth I'm severely disappointed. It's a pain in the butt to bleach. Doing it over and over with no results is just frustrating.