In which sentence is okay to abbreviate the word doctor?

According to Dr. Patel, toenails make take months to grow back.

I asked my mom if a dr. visit was really necessary to fix my toenail.

When my toenail was mashed by a falling log, I went to the dr. for advice.

Some drs. recommend wearing two pairs of socks until the injury heals.
HELP PLSSSS