Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern... As per your complain and presentation of symptoms pain after Post placement in post and core treatment is due to a few common reasons like inflammation of the nerves in a region below the root tips of the tooth due to heat and pressure generated, while drilling flaring up of infection below the root tips of root canal treated tooth if already there was mild infection, cracks in tooth etc. Many a times acute infection cannot be observed by seeing an x ray. If there are no cracks, perforations visible in an x ray then infection seems to be the cause and surgical treatment that might be advise to you is Apicectomy. Nothing to worry, as it is a minor surgical procedure and tooth can be treated very well by it.. As there is throbbing or pain then treatment can be proceeded only after relieving pain and you should definitely get the treatment done.. First of all you can take a short course of antibiotics and painkillers like amoxicillin antibiotic and Ibuprofen painkiller.. If the throbbing completely subsides and does not return in next one week you can proceed with post and core, but if you still have pain and discomfort then Apicectomy has to be done. Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora.