Though there is no harm in scuba diving with braces on but you should take care of the following things....

If you are wearing rubber bands in your braces from jaw to jaw, i recommend taking them out for the dive.  Wiggling your jaws to cope up with ear pressure may cause the rubber bands to snap and get lodged somewhere in your mouth or possibly swallowing.

Also practice in a small pool before going for scuba....For more info on braces see the link...http://www.identalhub.com/articlecategory-braces-21.aspx