Oral thrush is a term for candidal infection which is a fungal infection. In such cases immediately visit a dentist
If it is only a ulcer, it can be due to dehydration or stress or gastric disturbances or due to irritation from sharp teeth edges
Next Steps
Apply mucopain gel on the ulcer, drink lots of fluids, of sharp teeth edges are present, get it trimmed at a clinic
Health Tips
Oral thrush is a major complication, and should be handled by professionals only. Kindly do not ignore