Treating difficult upper first molars

Oct. 1, 2009
I recently received this letter from a reader. It raises an excellent question and is the subject of this month's column.

by Richard Mounce, DDS

For more on this topic, go to and search using the following key words: principle–driven endodontics, rubber dam, Dr. Richard Mounce, The Endo File.

I recently received this letter from a reader. It raises an excellent question and is the subject of this month's column.

“Richard, your articles in Dental Economics® are always educational and I pick up pearls from just about every column you write. Thank you! I do have a question that I'd appreciate your thoughts on. You describe how difficult upper first molars can be to treat with MB2, especially having two patent canals apically. Does that mean God has started building teeth we cannot fix? Does that then mean initial RCT, followed by future retreatment, followed by future apical surgery, and possible future extraction and implant placement/bridge fabrication on these teeth? Any insight as to how we can determine this before we start that process, if that's the future of these teeth? Probably not yet with our level of technology ....”

AThe upper first molar mesial buccal root is the most technically challenging root in the mouth to treat endodontically. This is not to imply or assert that the root cannot be treated well or that the outcome(s) listed above is an eventuality. MB root treatment should be carefully planned before starting the case. Both the risks posed by the root (perforation, ledging, blockage, file fracture, etc.) and the equipment and skills needed to address these risks should be considered before treatment begins.

In essence, the root can be treated with predictable success, but it must be treated correctly as the MB root is less forgiving in the event of clinical mismanagement than many root forms and requires a higher level of care. Hence, the MB is not a clinical event that can be rushed.

The single biggest challenge clinicians have with the MB root and the MB2 is that they have not achieved straight–line access as a first step in canal location, and secondly, they often do not have the lighting, visualization, and magnification needed either to find or manage the MB2 canal correctly. If they do find the canal, they often try to initially negotiate it with too large of a hand file.

Sequential steps in MB2 management are essential, first achieving straight–line access, and secondly, uncovering the isthmus between the MB1 and MB2. If the shelf of dentin over the MB2 is removed correctly and conservatively, the clinician can often see the location of the MB2 quite clearly and be guided to the correct place in which to insert the first hand file to negotiate the canal.

Once located, the smallest hand file possible, a No. 6 or a No. 8, should be slowly and deliberately worked up the canal. If the MB2 canal will not allow easy negotiation, it is often beneficial to enlarge the MB1 first to completion and then attempt to negotiate the MB2. This entire process is made infinitely simpler when the clinician is able to see the MB2 with the use of a surgical operating microscope (Global Surgical, St. Louis, Mo.).

Once a No. 6 or No. 8 hand file is able to enter the MB2 to the apex, reciprocation in the form of an M4 Safety Handpiece* can easily and efficiently enlarge the MB2 and ready it for RNT enlargement. I use the Twisted File* for canal enlargement, and most often will finalize the taper for the MB2 to a .06 and an average master apical diameter of No. 40 or as required by the particular canal.

If the clinician cannot easily reach the apex of the MB2 canal, it has value to precurve the hand files and continue to insert them in different orientations until they are sure that the canal is not negotiable or it becomes so. This will take time and diligent effort.

The reader asks if there are ways to determine the clinical difficulty of the MB2 before starting the case. The short answer is no, because the difficulty of negotiation of the MB2 cannot be determined in advance of access. Younger patients with vital irreversibly inflamed pulps may have slightly easier negotiation of their MB2 canals, but such a generalization can become meaningless in any given clinical case.

It is noteworthy that if the clinician can visualize the orifice and yet not negotiate the canal, that the further below the pulpal floor the access is taken to uncover the canal, the greater the risk of perforation. There is a risk/benefit decision point at which the clinician is advised to stop dentin removal on the pulpal floor in searching for the MB2.

The lesser of two evils is to leave an MB2 non–negotiated rather than create a perforation on the pulpal floor searching for an MB2 that is never located. If such a perforation were to occur, it is highly unlikely that the MB2 will be made negotiable after the perforation, even if the perforation were to be repaired.

I welcome your feedback.

*SybronEndo, Orange, Calif.

Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash.

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