Scuba diving with dental braces in a young adolescent should pose no problem. Neither teeth nor braces are compressible, so the depth of a dive, or the pressure that is exerted on a body air space, like a sinus, should not present a problem.
That is not to say that a new diver with braces won't have some soreness or aches after scuba diving. Braces gradually realign the position of an individual's teeth over the course of many months. At any given time, most of the teeth are still mobile.The act of biting down on the bite block of a scuba regulator mouthpiece for a prolonged period of time may produce a little extra stress or tension on a young diver's teeth that are still being realigned.
This may produce a little soreness or tenderness after a couple of dives and perhaps a little jaw fatigue in a new diver. Any diver should be able to properly grasp a regulator mouthpiece for the duration of a dive or series of dives without difficulty in order to dive safely.
Note: there have been reported incidents of tooth squeeze in divers when an air pocket has developed in a loose filling or through tooth decay; the air expands upon ascent and can cause pain and even break through a filling. For more information on this see "The Rarest Barotrauma" by Laurence A. Stein, D.D.S., in the September/October 1993 issue of Alert Diver.