It could be any of a number of reasons. I assume it was a lower tooth,
since these are the most difficult to get numb.
Your tooth was abscessed or had a severe inflammation of the nerve
inside it. These "hot" teeth are sometimes very difficult to numb
properly, especially for the procedures required to get rid of
toothache (root canal treatment or extraction) which need a greater
level of anaesthesia than say simple fillings.
Your tooth may receive accessory ennervation, meaning that there are
some "extra" nerves going into it that are not numbed by the regular
techniques. This is not extremely uncommon and there are alternative
techniques designed to circumvent such problems, but may require some
"experimentation" to figure out which technique has the best results on
you.
If you didn't have problems with getting lower teeth numb enough in the
past, I would tend to think that the abscess or inflammation was the
problem. Incidentally, each shot delivered at the same spot has a
decreased effect so that after a number of shots additional ones will
wield no further benefit.
In my experience, a tooth that will not get numb whatever I do on the
first appointment may prove very easy to get numb a few days later.

Regards,
George

Its technique ... and anatomy. Try a male dentist ..... we are mor
experienced with both!

Joel

--
Joel34

An infection could block the effects of the novocane shot. Usually
antibiotic treatement a week before allows the local anesthetic to take
affect.

Thanks for the info guys. BTW the Dentist and receptionist were very
attractive but I'm happily married. She referred me to a Dentist right
across the street who surprisingly had no idea who she was. He gave me
NO2 and I had no problems. Was still in pain the next day so went
back. Turns out she had started work on the tooth behind the one that
hurt. He finished what she started but did not fix the tooth giving me
pain. So he looks in my mouth and says "Oh this tooth is cracked, it's
gotta come out".  I think I cracked it because I went into seizures
after I made the mistake of taking Hydrocodone and Lyrica(it's for
diabetic seizures). My Dad and my Denist both scolded me for that one
but being that much  severe pain I was ready to try anything.
Especially late at night ready to burst into tears. Stupid move.
Well $1800 later I have an implant and very minor discomfort.
Still can't eat much though and I had just been to the grocery before
the surgery... damn. Tanks for listenig, mark