Stress
There will be days when you have your favorite patients spaced out with enough time to take a break, discuss The Bachelor with your co-workers, or get in a game of Candy Crush.
Then there will be days when you're absolutely slammed with patients, back to back. They'll be the whiny kind with seriously bad gingivitis that is impossible to clean in a forty-five-minute appointment.
Those days are stressful, which only makes the pain in your back and wrists worse.
Then again, you probably have the next day or two off. Go to the beach, or the spa, and unwind until you stop thinking about filthy molars, or at least until your wrists stop throbbing.