Need a root canal and crown, will I be setting myself up for parasites?

I went to the dentist this week and was informed that a tooth that had been bothering me, that had been filled and refilled with a composite filling, had to have a root canal. The root is dying and thought not infected yet, I was told will eventually die altogether and that I need to have a root canal done and then have a temporary crown put on then a permanent crown put on. I watched the video and understand the "process" but what exactly does the endodontist fill the empty space after a root is taken out with? Is this the stuff that parasites love? And my crown will be a composite, what exactly is that made of? If it is a composite does that lessen my chance of parasites? Any information or advice would be much appreciated, thanks. Tweet