Partial Root Canal falling out?

I have been getting these chunks of crunchy white things in my mouth.  I only know they are there when I talk or just bite down, especially when I haven't ate in a while.  They're pretty tiny, but I'm worried that it may be my partial root canal that I had done about 4 years ago on my upper, middle molar on the right side, it's the second molar from the front on the top right side.  I was supposed to get it capped, but I didn't go back because the women at the front desk were really rude at that dentist office.  These pieces are white on one side and then a grayish color on the flat side.  They don't taste or smell like a rotten tooth.  Which I have had before.

If these are just the filling, would I have any pain if it completely came out?  I'm not sure how far he drilled into my tooth and I'm not sure if he even took out the nerve like with a full root canal.  Also, is there anything I can pack in it until I could get to a dentist if it did completely come out?  I may not get to go to a dentist at least until after Christmas.  Should I brush my teeth that are near it or not, just so I can prevent it from coming out?  Should I avoid eating anything on that side?