Root Canal treatment (RCT) has become the standard of care in restoring compromised teeth back to form and function. One of the common causes of failure of RCT is under filled or missed root canals. And today I want to share one of my case about the retreatment because of RCT’s failure. A girl came to my office concerning about her tooth still have swelling and pain after the RCT had been done. The radiograph was take to comfirmed the previous RCT had underfill of obturation on a maxillary central incisor which the swelling origin. Inadequate abturation in root canal can lead to untreated root canal spaces, which in turn acts for bacterial contamination and failure of treatment. After the retreatment on maxillary central incisor of root canal, there was no swelling and pain that been reported.