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J Can Dent Assoc. 2002 Jan;68(1):28-33.

Location of canal isthmus and accessory canals in the mesiobuccal root of maxillary first permanent molars.

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  • 1Department of Dentistry, Faculty of Medicine, University of Alberta, Edmonton.



Failure in surgical endodontics may be caused by many factors. Failure is commonly due to improper preparation for the root-end filling and a lack of seal of the resected root end. The aim of this study was to investigate the morphology of resected mesiobuccal (MB) root ends of maxillary first molars and to evaluate the location of the canal isthmus and accessory canals between the MB canals.


From 50 selected first permanent molars, sections of the MB root at 3, 4 and 5 mm from the apex were prepared, acid-etched, washed and dried. The apical side of each section was sputter-coated with gold, examined by a scanning electron microscope and photographed.


Overall, 18 (36%) of the 50 MB roots had one canal, whereas 32 (64%) had 2 canals. Of the roots with 2 canals, 10 (31.25%) contained either a complete isthmus or accessory canals or both between the 2 main canals. Another 10 (31.25%) showed partial isthmus formation.


MB roots exhibit a variety of canal configurations. On the basis of these findings, we propose a classification of the resected root surface of the MB root. Prudent judgement in preparing the canal isthmus, meticulous skill and comprehensive knowledge of root canal anatomy are essential for successful treatment.

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