What are the causes of numerous mouth sores? and how can it be cured?

Diagnosis needed: In order to even list the possible causes of "mouth sores" would require a list too large to even list on this site. The "cure" if there was one (or treatment\prevention) would obviously depend upon the cause. If you have or suffer from repeated multiple mouth sores, you need to consult a dentist and\or physician when you have these sores for a personal clinical evaluation.

Multiple apthous : May be a case of multiple apthous ulcers. That is the most common cause. It is self limiting, 7-10 days duration. Lasers can help.

Unknown cause.: Agree. Aphthous ulcers. Sodium lauryl sulfate (a soap commonly found in toothpaste) exposure prolongs healing time. Dexamethasone ( ? Steroids in general) speed healing. Consider compounded mouthwash 2 tsp 4-6 x per day swish and spit. 100 ml Dexamethasone 0.1 mg/ ml elixir 100 ml Diphenhydramine 2.5 mg/ ml elixir 90 ml viscous Lidocaine 2% 60 ml Nystatin 100, 000u suspension.