This is a legitimate question since there are people with braces who would love to play the harmonica, but they believe that the braces could be in the way. The truth is that playing the harmonica requires you to put the instrument in your mouth, and you must close in any possible way for the air to get out.
This can be particularly tricky when you’re wearing braces. But a bit of practice can take you a long way. If you are beginning, you may feel like you have a severe handicap because you wear braces. However, by struggling a bit in the beginning, you may become a better harmonica player later on, compared to others.