zingers [SEP] i used zoom whitening years ago and got zingers that evening i ve used my retainer trays and gel bleach purchased from my dentist here and there since i just finished my invisalign and wanted to treat myself i had my first treatment at my orthodontist s office and purchased the take home kit same as this item i got zingers despite claims that it s pain free i took tylenol promptly and have only felt a couple more but they do happen talked to a couple of others who ve used glo and they too got zingers the manufacturer has been told about this and claims these folks are outliers i d do it again because the results are great but take tylenol preemptively and plan to not eat or drink anything hot or cold in the first days