mouth rot isnt contagious is it? idk if a biopsy of mouth tissue would be nessasary... it sure as heck will be expencive to have that done. simple baytril and daily/as needed cleaning will take care of any mild case. i had a water dragon with exposed bone with no infection or mouth rot, just simply exposed bone on his jaw. started with rubbing his nose and eventualy pulled his skin down to where you could see a good 1/16 of an inch of his bone and he lost teeth. i kept him on baytrill for 2 months every other day, low dose, and kept the area clean with antifungle.
http://www.healthypets.com/zylmedskinth.html this stuff is amazing i highly recomend it, it can be ingested.

your dragon may use this, but dont take this as a substitute for seeing the vet, you need internal antibiotics to cure any internal infection. baytril is a nice mild wide spectrum antibiotic that can be injected or given orally.