There's a white substance on both inner cheeks, right behind the bottom row of teeth. I did a swab and it came back clean. I showed the dentist and she said it's
Canker sore - Symptoms and causes - Mayo Clinic
White Spots on Gums: 6 Causes and How to Treat Them
I have some white patches inside my mouth (both inner cheek) they look exactly like ulcer. But it doesn't hurt nor bothering me. I'm worried cause I have this for months now.