If this is in the upper premolar or first molar area, your dentist
doubtless damaged a vein in the pterygoid venous plexus.  I've seen this
only once--the patient in the cubicle next to me in dental school.  I
think the instructor may have given the injection.
    It's almost certainly just one of those things.  You have to stay close
to the bone  to try to avoid the plexus.  My guess is (based on the
rarity of this happening) than unless you have a very unusually
prominent plexus this is unlikely to happen again.
    You probably should be followed by an oral surgeon to manage the
hematoma, and may need to be on antibiotics to lessen the chance of
infection.

Steve

I went in to the dentist to have 2 root canals done, side by side. The
one came out ok. Then he started working on the other one. Then the sh__
hit the fan.

I let out a scream and within moments my right cheek swelled up so big I
look like a freak show. By that night, not only was I all swelled on my
cheek, jaw and down my neck, I was also black and blue.

Did this guy know what the heck he was doing or what? He said as a
result of the needle hitting a vein, it was hematoma.

Now, I have had many root canals over course of time. But never like
this. Talked to many people and they are shocked too

He never did get the chance to finish it. And I had to be out of work
Thursday and Friday taking sick leave. Could hardly open my mouth to
talk. Let alone not being able to eat much of anything

I am at a loss here, and don't know whether I should go back and have
him finish it (and hit another vein) or find someone else. Really confused

Any suggestions?

Susan