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Although the cause of most mouth ulcers is unknown, accidental damage is a common reason. For example, biting the tongue or cheek lining by mistake, eating foods that are too hot, a sharp broken tooth, or wearing badly-fitting dentures can all produce a mouth ulcer.
Avoid spicy, salty or sour foods until the ulcer has healed.
Dissolve a tablet of soluble (dispersible) paracetamol
in water, and swirl it round your mouth before swallowing it.
Before eating, rinse your mouth with iced water. This may dull the pain, so that eating is more comfortable.
tablets taken under the tongue (sublingually) may help, even in people whose blood level of vitamin B12 is normal.