Some patients may experience discomfort and sometimes pain after treatment that subsides within a few days after treatment. luckily, only a small minority of patients experience severe pain which is sometimes accompanied with a swelling. This is an unfortunate post-treatment condition called a flare up. A flare up is a body reaction to endodontic treatment of infected teeth. It is believed to be the result of infected debris inadvertently expressed into the surrounding area of the tooth. The body attempts to clear up those debris with an inflammatory response that cause pain and sometimes a swelling. Usually a flare up clears within a week of its onset. Your endodontist or dentist can help you through any postoperative pain or discomfort you may experience by prescribing painkillers or in a flare up situation, a visit to the dental surgery may be needed.