Hi there...mouth ulcers take sometime to heal, about 1 to 2 weeks. They usually spontaneously heal, but sometimes topical steroids like triamcinolone acetonide might be required. But you must remember that there are a lot of causes for oral ulcers like herpes, behcets syndrome, nutritional deficiency, pemphigus, candidiasis, etc. So if the lesions are recuurently occurring, then it best you visit a dermatologist for further evaluation.