Hello:)Thank you for choosing HCM. You did not mention if he is under medication for general health. (Check with the physician reg. this if any).Some drugs can also cause mouth ulcers. A clear cause for ulcers has not been given yet,however poor oral hygiene, stress, deficiencies can attribute. He can use a lignocaine based gel like GUMTONE before food(this makes the area little numb, for temporary relief). Gargle thrice daily with warm saline water. Use a soft tooth brush. Have a tobacco free,non-alcoholic, stress free life style. Check if any sharp tooth causes this ulcer,if so it should be rounded. Regards.