Hello sir!
The condition is called as bruxism- clenching/grinding. That area become white after repeated clenching. If you grind your teeth while you're asleep, mouth guards/splints may help you. It will cost around 2000 per arch. If it is due to dental problems like buccally(outwards) placed upper teeth and if they are sharp, they have to be treated.
Next Steps
Visit your dentist immediately.