I live in New York and I have this friend that is not quite so smart as he thinks he is. He though that if he got whitening strips that whiten your teeth in seven days that if double the amount of time he was to keep them on he would whiten his teeth even faster. Now his teeth really hurt and he says it hurts to any thing hot and cold. He worried now he made have messed up his teeth. Will his teeth go back to normal over time or should he see a dentist about what he did?