What is the treatment of aphthus. oral ulcer?

Alkalinize mouth: Decrease acids that you eat or drink. Stop coffee, tea, sodas. Drink only water. Get some antacid liquid like maalox or mylanta and use a tablespoon of it swishing and rinsing for 1 minute after each meal and before bed. Decreasing acidity in the mouth helps to heal and prevent these ulcers.

Ulcer: Not much! the duration is short and the therapy should just be with topical anesthetics. Major aphthous ulcers are different and require medical attention and possible admission with IV administration.