Sometimes my mother mouth breaks out in white sores what is that? her dentist was not able to figure it out.

See an Oral Surgeon: She should be seen by an oral surgeon or oral pathologist when those white sores are present. A biopsy would likely provide a clinical diagnosis. Blood tests and an exam by a physician might also be wise if the diagnosis is not easily determined by a visual exam or biopsy report.

White mouth sores: There are a number of conditions that can result in white lesions in the mouth. Two of the most common are thrush (a yeast infection) which could happen after a person takes antibiotics or if the immune system is not working properly, and lichen planus, an inflammatory condition of the mouth and possibly the skin. There are many others. Please see dermatologist for a proper diagnosis.