You might not think a dental assistant job is especially rewarding. After all, you're in cahoots with a dentist who gets paid to inflict discomfort and (sometimes) pain. Many patients would rather suffer through an IRS audit than sit in that dental chair. You might get bitten, drooled on, or sneezed at (or maybe all three at once).
On the other hand, you might help ease a young patient's fears during her first dental appointment. You may help the dentist repair a broken filling so an older patient can eat normally again. Your steady hands and calm, competent manner can help keep the dentist on track throughout his hectic appointment schedule. In your own small way, you're contributing to a better quality of life for everyone you encounter.