Here’s a trick i use to prevent the MTA from slipping into the canal when the perforation is very close to the canal. This maxillary first molar had a missed Mesio-buccal canal with a perforation. After locating the mesio-buccal canal and cleaning it, the canal was filled with calcium hydroxide. A gutta percha cone was then placed into the canal and sheared off at the coronal level. The perforation was sealed with MTA, a moist cotton pellet was placed in the pulp chamber and the access closed with GIC. After 1 week, the temporary filling is removed and the MTA checked for hardening. The gutta percha placed in the MB canal is then removed with a rotary ni-ti file. The calcium hydroxide placed in the canal is removed and the canal is obturated with gutta percha. A composite core is placed.