12 years is really very long time for this stubborn ulcers. Kenacort
and other topical gels will not work in these type of ulcers. May be oral tablets or capsules can work. But not without proper diagnosis. If you have ulcers at other body parts like eyes, gonads, stomach, intestine etc, you required thorough investigation for actual cause of oral ulcers. If they are limited to mouth only and changing place of occurrence each time (recurrent Aphthous stomatitis), it can be cured permanently with advanced LASER
ablation. Visit or consult dental oral medicine and /or periodontist
specialists in your area.