Tricky Anatomy of Mandibular First Molars written by: David M Reeves, DDS, CAGS


In this email I thought a little refresher on the anatomy of the mandibular first molar would be exciting. It becomes even more exciting when some anatomy is missed. 
A classic study on root canal morphology (Skidmore and Bjorndal, 1971 Oral Surg) found that the canal configuration of the teeth studied resulted in these following percentages: 7% (6.7%) had two canal systems, 65% (64.5%) had three canal systems, and 29% (28.9%) had four canal systems. In 60% (59.5%) the mesial canals remained divided throughout the length of the root. In the other 40.5% the mesial canals joined in the apical third of the root and had a common foramen. In 38.5% of the distal roots with two canals, the canals remained separate, each having an apical foramen. In the other 61.5% the two distal canals unite and terminate in a common apical foramen.
The number in ( ) is the actual percentages. I like to round the numbers as a memory aid. Different studies result in variance of the above percentages. 
As a rule of thumb, 30-40% of mandibular first molars have at least four canal systems.
The take home message is always plan on at least four canal systems in a mandibular first molar, and be aware that they might all have separate POE’s (Portals of Exit).The importance of planning for the occurrence of two distal canal systems is the influence it has on access preparation, in allowing adequate space for visualization and exploration. Often the DB canal can be like a “flying buttress” and sweeping the DB aspect of your access toward the buccal is a good way to check the anatomy. A high percentage of endodontic failure is incomplete removal of the canal contents and untreated anatomy. 
Rare Creatures written by: Randall J. Iwasiuk, DDS


Three canal maxillary second premolars are quite uncommon . They occur in 0.66-1.0% (1) of maxillary second premolars, depending on whom you believe. As you can see they can be tricky to discern in pre-operative radiographs. As always good radiographs are a prerequisite to anticipating factors that may complicate your cases. These anatomical rarities occur infrequently so you won’t get many chances to bag some real trophies, so when you do be ready for them.
1. Vertucci, FJ. Root Canal Anatomy of the Human Permanent Teeth.
    Oral Surg. 1984; 58: 589-599.
Snagging the Big One written by: David M. Reeves, DDS, CAGS


I just completed treatment of this tooth yesterday and got kind of excited about the palatal anatomy. So I thought second molars would be a good topic. The palatal canal anatomy of maxillary second molars can be very interesting and exciting at times. Particularly when your instrument gets snagged on something, and the canal system doesn’t present the typical tactile feedback. Due to the diameter or the root and the large vascular space many of these palatal systems contain bifurcations, trifurcations, anastomoses, or deltas. One study found that two palatal roots and two palatal canals occur in 1.47% of these teeth.So remember if something feels unusual it probably is, so live in the moment and go exploring. You might find something exciting.
1. Peikoff MD, Christie WH, Fogel HM: The maxillary second molar: variations in the number of roots and canals, Int Endodon J 29(6):365, 1996.