An anatomic investigation of the mandibular first molar using micro-computed tomography.

By Harris SP, Bowles WR, Fok A, McClanahan SB.

Date: 01/2013
Journal: JOE


Examine the anatomy of mandibular 1st molars using micro CT.


Subjects: Extracted Mandibular First Molars

N = 22

Micro-CT was scanned, reconstructed, and linear measurements were made to determine the following:

1. Assess the relationship of canal orifices to one another just below the pulpal floor to aid in canal identification upon orthograde access

2. Verify the cross-sectional width of the canals along the length of each root to advance the understanding of the working width in this tooth

3. Measure the thinnest area of dentin on the furcal aspect along the length of each root

4. Document the presence of lateral canals and apical ramifications in each root

5. Record the presence, type, and location of isthmuses in each root


1. Pulpal floor anatomy:  Distances between canals

  • M canals ranged 1.4 -3 mm
  • D and M canals averaged 4.4 mm

2. Furcation Dentin thickness:

  • M- average minimum= 1.28 mm
  • D- apical 6 mm ranged 0.25- 1.5 mm

3. Canal dimensions: BL consistently wider than MD in both roots

4. Canal morphology:

  • M canals highly variable: 23% 2 canals, 9% 1 canal, 36% more than 2 canals
  • Distal: 82% single canal and 9% two canals.

5. Isthmuses: 100% in M and D (those w/2 canals), ranging 3- 8 mm from apex

6. 79 % of apical and lat canals will exit in the apical 3 mm of M and 91 % in D

Clinical Significance:

  • The furcal aspect of the entire mesial root should be considered a “danger zone”
  • Mesial canals were found to be much more variable than distal canals in morphology, though orifice location remains relatively consistent
  • Root-end resection of 3 mm would remove the majority of lateral canals and apical ramifications.