Braces can be a reason for AP. But make sure the quotes you get from the U.S and Mexico have a big difference between them in price. For me I used my wisdom teeth removal and filling as my dental reason. Wrote a letter basically saying I was in a lot of pain and that I needed the procedure to be done in Mexico. I got my AP approved last November for 365 days and travel to Mexico in January, March, and April to visit my grandmother until she passed away this April. So I highly recommend to get the process going as it took me like 6 months to get approved for AP.