I'm 20. My cortical jaw bone has a noticable and sudden shrinkage. What might cause this? Any answer will help. Even a crazy one. Please?

Bone changes slowly. Bone cannot suddenly shrink nor suddenly grow. That means one must sit back, gather the last 5 years of candid snapshots, and study them for a while... to figure out what would make a person perceive his jaw bone got smaller. It may be that something else got bigger, thus making the bone look smaller. Then, an appointment with an ENT doctor will help (bring the best series of snapshots along).