It isnt very clear. It maybe an ulcer due to cheek bite especially if any teeth are sharp. Kindly watch out for any habits and if its associated with fever andifvhe changes his toothpasterecently. . Systemic issues like
vitamin b deficiencies, gastric reflux and anemia can cause recùrrant ulcers too . Stress, spicy food, hard foods, lip biting, trauma from toothbrushes, are the common causes.
Next Steps
kindly visit a dentist for a clinical examination especially if an ulcer doesn't heal in 2 weeks. it's better to verify if it's an ulcer with clinical examination
Health Tips
Avoid very hard, hot, spicy and acidic foods until they heal.keep him hydrated