Comparison ucer erosion continuity of broken superficial epithelium severe basal cells involved free border clear unclear diseases RAU Pemphigus Behcet's disease Herpes simplex Syphilis BACKulcer erosion continuity of epithelium broken severe superficial basal cells involved free border clear unclear diseases RAU Behcet’s disease Syphilis Pemphigus Herpes simplex BACK Comparison