I got in an accident where by top two front teeth (central incisors)
got avulsed. They were not knocked out of my mouth, but they were in
pretty bad shape, crooked, and almost out of their sockets...

I went to the emergency room within an hour of the incident and they
were set back in my sockets, although one of them was not completely
set back, and I could not bite down normally.

The next morning I went to my dentist, and he splinted them, and set
them in better... Now, a month later, my dentist is urging me to have
root canals on both teeth, despite the fact that they look fine.

My dentist says that resorption will occur if I do not get root canals
done, and that the roots of my teeth will rot away, and my teeth will
subsequently become loose and fall out.

I was hoping that perhaps my nerves and blood vessels would reattach
themselves to the teeth.... I didn't exactly understand the concept of
resorption. I asked my dentist but he seemed to become impatient with
my questions.

If my nerves and blood vessels in the roots of my teeth disolve away,
what's the big deal? Then my teeth would presumably become discolored,
and then I would know for sure that I need a root canal.

What exactly is resorption, why is it bad, and how would a root canal
stop it from happening?

Thank you,