Abstract
This case report is to present a maxillary first molar with one O-shaped root, which is an extended C-shaped canal system. Patient with chronic apical periodontitis in maxillary left first molar underwent replantation because of difficulty in negotiating all canals. Periapical radiographs and cone-beam computed tomography (CBCT) were taken. All roots were connected and fused to one root, and all canals seemed to be connected to form an O-shape. The apical 3 mm of the root were resected and retrograde filled with resin-modified glass ionomer. Intentional replantation as an alternative treatment could be considered in a maxillary first molar having an unusual O-shaped root.