<s>[INST] Hello doctor, I had a root canal done five months back. I started to experience pain yesterday where the crown is, and overnight the pain got severe. The crown feels sensitive when I touch it. So I am afraid there is an infection underneath it. My dentist is closed for the weekend. Nothing I do stops the pain. My regular doctor said she would need an X-ray to confirm an infection. [/INST] Hi. I understand this would be a very painful condition. If it has started with pain so hard inside the crown then infection has definitely occurred. In such cases, re-treatment is done with a very poor prognosis or tooth extraction is done that rules out the cause of infection with 100 % prognosis rate. Things to do right now include taking Ibuprofen 600 mg TDS (thrice a day, that is, eight hourly for three days). Start saline water mouthrinses 4 to 5 times a day. (Take a cup of lukewarm water and add 1/4th teaspoon of salt in it and do its rinses). Do not lay down straight. It will trigger up a toothache. Keep pillows a bit high or some more cushions under your neck while trying to sleep. If only painkiller Ibuprofen does not help much with pain in a day, then you must start with this antibiotic regime as soon as possible. Tablet Augmentin 625 mg BD (twice a day), tablet Gramex (generic: Metronidazole) 400 mg (twice a day), tablet Ibuprofen 600 mg (thrice a day). That is the best regime to be followed in tooth infections provided that you are not allergic to any of such medicines. Hopefully, it will help. </s>