It may be malpractice: it depends on whether, 1) based on the symptoms and what was observable at the time, a reasonable dentist would have known of the infection; and 2) if the dentist did or should have known of the infection, would standard accepted procedure have been to treat wtih antibiotics first, or would it be considered acceptable to not treat. If the dentist did not known and reasonably would not have known of the infection there would be no malpractice; and even if he did know, if an accepted procedure would have been to do the root canal without first treating with antibiotics, again, there would be no malpractice. It's only if the dentist did something wrong by contemporary standards that there may be malpractice.You need to consult with another dentist to get an idea of whether this was malpractice by current dental standards or not.Even if it was malpractice, it may not mean that you have a viable case. You can only recover the additional medical costs caused by the malpractice, lost wages, if any, and "pain and suffering" for life impairment, disability, or disfigurement lasting at least many weeks (if the problems last for less than many weeks, you'd get so little money as to not make a lawsuit worthwhile). But malpractice suits can be very expensive to bring, since you need to hire a medical (dental) expert witness, and they do not work cheap. If as we hope, this resolves in a few more days or week or two, without excessive medical costs, a malpractice suit would almost certainly cost you far more than you could win.