Yes, you need to pay for the procedure. On the other hand, you could also sue the dentist for any additional medical costs (if any) you incurred due to his negligence (carelessness), like the emergency room costs, antibiotics, etc.; for any work or wages you missed; and possibly for some small amount for pain and suffering. Your claim against the dentist for these things, and his claim vs. you for the money, are independent of each other legally; that said, as a practical matter, if you explain that you will sue if you can't settle the matter, he may agree to a settlement in which you each give up your claims (including his claim for the cost of the procedure) against each other and go your separate ways.