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The maxillary second molar: variations in the number of roots and canals.

A retrospective study was undertaken of 520 completed endodontic treatments of maxillary second molar teeth which were selected from a specialty endodontic practice. Radiographs were reviewed and studied, a classification of antomical root and canal variations was devised, and the frequency with which each variant occurred was recorded. There were six variants which occurred frequently enough to be considered as separate anatomic categories and their frequency of occurrence is illustrated. The six variants found in the study and their frequency of occurrence are as follows: (1) three separate roots and three separate canals (56.9%); (2) three separate roots and four canals (two in the mesiobuccal root) (22.7%); (3) three roots and canals whose mesiobuccal and distobuccal canals combine to form a common buccal with a separate palatal (9%); (4) two separate roots with a single canal in each (6.9%); (5) one main root and canal (3.1%); and (6) four separate roots and four separate canals including two palatal (1.4%). Clinical examples of these deviant variations are also presented.