How can i prevent painful mouth canker sores?

Can't: There's no way to prevent them, but you can help mitigate the discomfort by applying some topical medications that you can by at the drug store.

Laser treatment: A painless laser treatment sometimes can keep them from coming back in the same spot. While they might recur in other spots, over time and with a few treatments, you can significantly reduce them. See an experienced laser dentist.

Canker sores: Canker sores, also known as mouth ulcers or mouth blisters, usually heal on its own in about a week or two. You can use warm salt rinses directly on the sore to alleviate pain. If the sores continue to persist, or are large or painful, visit your dentist. Depending on the nature and severity of the sore, dentists can provide a prescription and antimicrobial mouth rinses to reduce the pain.

Change toothpaste: About 85% of canker sores are linked to the use of toothpastes that have a foaming agent called sodium laurel sulfate. Check the box or tube of toothpaste for this chemical. If listed try a toothpaste without this ingredient. My personal preference is a toothpaste called closys, but there are others available.

Aphthous ulcers: Try closys toothpaste, but you are likely to be disappointed. Most aphthae are of unknown cause. Sometimes there is a serious condition. There are numerous remedies which have been tried, such as prednisone, Colchicine . See a dermatologist if you need help.