"Yup, you have one of those old-school retainers," the dentist remarked. "Wow." Her gloved fingers probed the hardware. "Wow" is never what you want to hear from someone who sees thousands of mouths per year. Yes, I answered, explaining that I had the metal wire installed on six of my bottom teeth right after I got my braces off at 17. I'd gotten used to its smooth bulk over the years; I rarely thought about it. And then Sharon Huang, DDS, cosmetic dentist and founder of New York City’s Les Belles Dentistry, hit me with something surprising: not only did she suggest we replace the retainer, but that we remove it that very moment.