I travel for work (dental hygienist - travel to communities in need/ short staffed offices). What can I claim? Travel expenses, rent, car costs, groceries?

It would depend. If you are considered self-employed (free-lancer), you might be able to claim some of these expenses. If you are an employee, you would only be able to claim expenses that you were required by your employer to pay for, and you would need a T2200 form your employer.