Physical Danger
This is a grueling profession. You're on your feet eight hours or more in a day, scrubbing calculus and debris, using sharp pointy tools, and ultrasonic dental blasters to get as many patients scrubbed clean one after another.
Hand, neck, and back strains are bound to happen.
If you have a boss who expects you to work at a grueling pace without breaks, then tendonitis, back aches, neck stiffness, pinched nerves, arthritis, and carpal tunnel syndrome could all be in your future (source).
You also could be exposed to patients with blood-borne diseases, like hepatitis or HIV, so wear gloves and be careful with those pointy instruments.
Not to mention patients who show up with colds or the flu—wear a mask and stock up on vitamins.