By Dr. Liji Thomas, MD Reviewed by Lauren Ng Aug 12 2025 A new study shows the glow from tooth whitening often fades within a year, but whether you still love your smile may depend more on your personality than the shade of your teeth. Study:  Effect of personality characteristics on perception of tooth whitening outcome in young adults in long-term: a randomised, double-blind, placebo controlled trial . Image credit: PeopleImages.com - Yuri A/Shutterstock.com Tooth whitening is a common