You might also ask about oral sedation, which is much cheaper and tends to work well. I took something called Halcion for a dental procedure two years ago and I honestly didn't give a hoot about what they were doing. Also, something to consider is that often you do not get numb because you are anxious and somehow this can make it difficult for the novacaine to work well.
If you have oral sedation beforehand, the novacaine may actually be effective, or at least more so than it was for you in the past.

Nancy