Active duty Navy dentist here. At my Command, I work 0645-1600 on Tues and Thurs, and 0645-1500 Mon, Wed, and Fri (get out early for individual PT). Weekends are my own time. I have Dental Duty Officer watch one day per month (could be a weekend), which is like being on call for dental emergencies that happen after normal business hours. You just carry a cell phone, and if someone calls you in the middle of the night, you get in your uniform and drive to the clinic to evaluate and treat the patient. As for time off, in addition to being off on weekends, you get a liberty period (3 or 4 day weekend) associated with most federal holidays. You also get 30 days of paid leave per year.