What is the incidence and related factors of middle mesial canals in mandibular molars?

This summary is based on the article published in the Journal of Endodontics: Middle Mesial Canals in Mandibular Molars Incidence and Related Factors (January 2015)

Ali Nosrat, DDS, MS, Raney J. Deschenes, DMD, MS, Patricia A. Tordik, DMD, M. Lamar Hicks, DDS, MS, and Ashraf F. Fouad, BDS, DDS, MS

Context

• The aim of root canal therapy is to eliminate all irritants from the root canal system. These irritants include necrotic pulp tissue, microorganisms, and their byproducts. A detailed knowledge of the pulp canal anatomy is necessary to effectively clean and shape the root canal system. Mandibular molars are the most frequent tooth type to be endodontically treated ¹.
• Studies have shown several variations in the anatomy of mandibular molars that are thought to be determined by race and genetics ³. These variations include a separate distolingual root ⁴, C-shaped anatomy of the roots and/or canals ⁵, an isthmus between the mesiobuccal (MB) and mesiolingual (ML) canals ⁶, and a third canal in the mesial root known as the middle mesial (MM) canal ⁷.
• The reported prevalence of the MM canal in mandibular molars varies among studies. Methods of detection include plastic casts ², clearing ⁸, scanning electron microscopy ⁹, micro–computed tomographic (mCT) imaging ¹⁰, and use of a file under magnification ¹¹.
• Clinical studies show that magnification significantly increases the probability of locating and negotiating a second MB canal in maxillary molars ^13–15.
• To date, there are no studies that report the incidence of negotiable MM canals in mandibular first and second molars using the dental operating microscope.

Purpose of the Study

1. To evaluate the incidence of negotiable MM canals in mandibular first and second molars using the dental operating microscope for magnification.
2. To correlate the incidence of MM canals with variables including molar type (first or second mandibular molar), sex, age, ethnicity, and the presence of a second distal canal.

Key Findings

• Persistent endodontic infection can be attributed to difficulties in removing a bacterial biofilm from root canal ramifications, including isthmuses ¹⁷.
• The presence of isthmuses indicate a high probability of having uncleaned areas in the mesial root of mandibular molars after root canal treatment. Toure et al ²² showed that more mandibular molars were extracted after root canal treatment than any other tooth type.
• There is a higher incidence of negotiable MM canals in younger patients. Gu et al ⁶ showed a significantly higher prevalence (50%) of isthmuses in patients aged 20–39 years compared with 24% in patients older than 60. They also showed that the average ratio of a partial isthmus to a complete isthmus increased with age ⁶, indicating that clinicians should spend more time evaluating the pulp chamber floor area between the MB and ML canals to search for an isthmus when treating mandibular first and second molars of younger patients.
• Data showed no significant difference in the incidence of MM canals among different ethnic groups.
• Using magnification and careful tactile search techniques, the incidence of MM canals in mandibular molars was found to be higher than previously reported.
• The probability of finding and negotiating an MM canal in younger patients is significantly higher than in older individuals. Using the operating microscope is key to locating and negotiating MM canals.

References

List of references (PDF)