I started invisalign treatment this year. I am on my 14th tray(out of 40). I have been changing them every 5 days as advised by my doctor. I use acceledent as well. I haven't heard a single reason yet on this forum as to why I can't change them sooner. I find trays starting to feel loose on the 4th or 5th day. If the next tray fits me fine, then why should I continue using the previous one any longer ?