Novocaine (generic drug name procaine) can cause major problems if directly injected into the blood stream in large amounts and too rapidly (that is, injected directly into a blood vessel). Direct injection into the blood stream can cause a seizure, which in some circumstances could result in death. Direct injection into a nerve would not be deadly – the drug only works when it is injected in close proximity to a nerve, thereby inactivating the ability of the nerve to send pain signals. So, unless the dentist mistakenly injected the anesthetic into a vessel, no worries - unless of course the patient has an previously unknown allergy to the drug and has a severe hypersensitivity reaction (but that’s a whole different story).