Changes in the Location of the Second Mesiobuccal Canal Orifice After Canal Preparation in Maxillary First Molars

This study evaluated angular and linear positional changes of the second mesiobuccal (MB2) canal orifice in maxillary first molars and proposed a guideline for its localization. Twenty-eight extracted maxillary first molars with four canals were analysed. After access cavity preparation, all canals except MB2 were instrumented. The initial and final MB2 orifice positions were defined as MB2a and MB2b, respectively, following selective dentine removal and canal preparation. Standardized microscopic images were obtained, and the angle between the MB1-MB2 and DB-P lines, as well as inter-orifice distances, were measured using paired t-tests (α = 0.05). MB2 canals were identified in all specimens. The mean angle significantly changed from -21.84° ± 8.87° to +8.38° ± 8.95° (p < 0.05), indicating a mesial shift and increased parallelism. Mean displacement was 1.07 ± 0.39 mm. A DB-P-parallel direction may aid predictable MB2 localization in maxillary first molars.