Authors: Skidmore AE, Bjorndal AM.
Title: Root canal morphology of the human mandibular first molar.
Journal: Oral Surg Oral Med Oral Pathol
Date: Nov 1971
Citation: 32(5):778-84
Category: Anatomical Considerations
Evidence-based Ranking: 5
Purpose/Objectives: A detailed investigation of the morphology of the root canals of extracted mandibular first molars.

Materials & Methods: 45 extracted mandibular first molars from 17-22 year old males. Pulp chambers were coronally accessed, debrided with a fine broach, and then placed into a 3% H2O2 solution at room temperature for 3 weeks. Polyester casting resin stained with red pigment was used to make casts of the root canals and the teeth were decalcified in a 35% nitric acid solution for 10 days – not affecting the resin.

Results: Table I summarizes the data. 6.7% of the teeth had only 2 canals. 64.4% had 3 canals, and 28.9% had four canals. In 59.5% of the teeth, the mesial canals remained divided throughout the length, and 40.5% the mesial canals converged into one in the apical third with a common foramen. In 38.5% of the distal roots with two canals, the canals remained separate, each with its own apical foramen. In the other 61.5% with two canals, they united and terminated in a common apical foramen.

Author’s Conclusion: This investigation reports substantially more teeth with four canals (28.9% here vs. 4.0% by Hess). The author suggests always looking for a second canal in the distal root of a mandibular first molar. Changing the traditional triangular outline to a more rectangular outline will permit better visualization and exploration potential for a possible fourth canal.

Validity of Conclusion: Knowing as much about the morphology of a tooth and its root canal system is an invaluable aid in performing root canal therapy.

Reviewer’s Comments: A larger sample size would help, but the concept of always looking for a fourth canal helps perform more thorough treatment.