Its said citrus fruits,potato chips can cause apthous ulcers?these foods cause micro injuries to the oral mucosa? or its the heat in body?and whats the role of vitb12 supplement. does taking supplement makes oral mucosa stronger against such injury?

Injuries: "It's said" by who? I've not seen well refereed research to support "micro abrasions" or "heat in the body" as precursors to aphthous ulcers. No, supplements don't help, only create supplement-rich urine. For best results have well balanced diet, brush 2x/day for 2 FULL minutes, floss or water-pick daily. See your Dentist 2x/year for evaluation & professional cleaning.