The cause of tiny white mouth sores, also known as mouth ulcers or canker sores, is unknown, but tissue injury and stress are likely causes, and acidic and citrus fruits and vegetables exacerbate the condition, according to WebMD. Dental appliances, such as ill-fitting dentures or braces, can trigger these sores.
These sores may also be caused by underlying health issues, such as nutritional problems, vitamin deficiencies, gastrointestinal tract disease and an impaired immune system, explains WebMD. Crohn's disease and celiac disease can also trigger the production of canker sores. The sores are painful ulcers inside the mouth that may burn or tingle.