The human jaw can generate over 260 pounds of force at the molars, and unless this pressure is perfectly balanced it can throw the delicate balance of the jaw's muscles, tendons, nerves, and ligaments into disarray.
How Did This Happen?
THERE ARE SEVERAL FACTORS THAT COULD BE AT PLAY:
Stress is an important factor — it frequently increases muscle tension in the jaw, which creates imbalances over time
Any kind of physical trauma
Dental work, orthodontics
Any quirk in your eating habits, or grinding of the teeth
Or it might just be time — your mouth and jaw are made up of living tissue, and can shift as you age