I got mine — made of surgical stainless steel — from a set of used dental tools at a garage sale for 25 cents. It’s incredibly handy for inspecting missing fillings, infections, gum complaints, particularly in kids. And you can look for sharp edges on dental braces. There really is no other way to look deep inside the mouth. The key is to get a proper front-surface mirror, which some drugstore plastic versions don’t have. Otherwise at close range there is a slight double image which confuses the image.