Routine root canal procedure with the usual 4 canals were located, cleaned, shaped, disinfected and sealed with sealer and root canal filling material. The mesial root in the upper first molar has an MB2 canal 90% of the time. These canals are very small and sometimes difficult to locate. A surgical operating microscope is used to locate the canal systems. This tooth has 4 canals that reach 4 separate root ends. Often times the MB2 may join the MB1 system.