Mouth ulcers usually seem to occur where people are using toothpaste with fluoride in it.
When this is swapped for one that is fluoride-free, they seem to disappear quite quickly.
Fluoride free toothpastes include Kingfisher’s, Tom of Maine’s, Nelson’s Homeopathic, Euthymol and Aloe Vera.
I have been told recently that Kingfisher’s have now made one that is also Sodium Laurel Sulphate free! Even better.
I have also read somewhere recently that brushing your teeth with very hot water is better than using toothpaste at all!
I have found that people with mouth ulcers often have quite a lot of lead in their hair.
In this case Vitamin C and garlic would also help.