Hi.. Can understand your concern.. As per your complain if you have greying of a tooth followed by pain, they are clear symptoms showing that you have a deeply infected tooth which has progressed to the level that it has involved the pulp( the central portion of tooth containing nerves and blood vessels) and once the infection reaches the pulp the nerves gets inflamed causing severe pain. This infection also progresses from the pulp up through the root canals to the area above the root tips and causes infection there and leads to pus formation and thereby creation of DENTAL ABSCESS. When there is no escape way for pus it starts accumulating in the region leading to swelling, tenderness and pain on face. As you explained that you have a filled tooth which is turning grey it means either it has lost the filling and getting further infected in the similar manner explained above or there is formation of SECONDARY CARIES which occurs below the filling in the tooth and can infect the pulp and cause pain. I would suggest you to consult a dentist and get a clinical check up and x ray done so that the dentist can rule out the cause of pain and treatment can be decided that either the tooth can be saved or needs extraction. In case the tooth can be saved the treatment that can be done is ROOT CANAL TREATMENT followed by antibiotics and painkillers. Hope your query is solved. Thanks and regards.. Dr.Honey Nandwani Arora.