Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Yuck and Ouch

I am 19. I have used reg. crest white strips, and they worked fine. i figured, "hey, premium must be better right?" WRONG!within the first 15 minutes, your gums hurt. it lasts for two days , where your mouth is sensitive and hurts to eat. no way will i ever use all 40 strips.