To report a case of maxillary lateral incisor after root canal therapy with omitted and calcified palatal root canal as well as middle lateral wall perforation, and to investigate the standard of root canal treatment and the microsurgical treatment of lateral wall perforation.

A 40-year-old female complained of abscess on the labial side of her left upper anterior teeth for 1 week. Clinical examination revealed that maxillary left lateral incisor (tooth 22) showed fistula in buccal mucosa and resin complement in palatal lingual fossa. Radiograph showed that tooth 22 had single root with double root canal, there were two segments of high density in the root canal, the buccal root canal was filled to the apex, while the palatal root canal was missing and no obvious root canal image in 1/3 part of its apical segment. There was no low-density transmission image in the apical region. The high density in the middle 1/3 part of distal root broke through the lateral wall and was covered by a low-density semilunar transmission area. At the subsequent hospital visit, the palatal root canal was found under the microscope and dredged calcification, then root canal filling by warm gutta-percha obturation system were performed. MTA was applied to filled the perforations in the inner wall of pulp cavity. Conventional micro root canal surgery was used to clean up the inflammatory tissue outside the perforation, and MTA was used to fill the perforation.

Ten days after operation, the fistula disappeared. Follow-up X-ray after 4 months and 52 months showed high-density radiographs in the middle 1/3 part of distal root, the semilunar transmission area became smaller, and the bone density was higher.

For the case of endodontics root canal treatment, radiograph should be carefully read before operation. If the semilunar low-density transmission image around the lateral wall of root canal is found after the operation, the lateral wall perforation should be considered, MTA filling and sealing perforation or micro root canal surgery should be carried out together with closely observing.