Patient referred by a colleague for root canal therapy on a maxillary second molar. Key tooth to save for a planned fixed bridge. History of throbbing pain in the last days. Keeps awake at night. Diagnosis: irreversible pulpitis. Findings: deciduous restoration, caries, severe pulp calcification. Problem to solve: locating and negociating root canals. The calcified dentine must be carefully removed with long thin ultrasonic tips under the high magnification of dental operating microscope(DOM). No rapid technique exists for dealing with calcified root canals. Last X ray follows Clark’s rule with a 20 degrees angulation and shows all 3 apices. Canal lengths: P 17 mm, MB 18mm, DB 18mm. Gutta percha and Pulp Canal Sealer. Lateral and vertical condensation. Provisionnal filling mat.: Cavit.