Claudia Hoffman
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PATIENT presented to our office with the chief complaint, “I had a root
canal started on tooth # 14 eight months ago, and it was just completed
a month ago. I have been in agony ever since it was started.” The medical
history revealed the patient suffers from trigeminal neuralgia on the left
side. The clinical evaluation revealed a normal intra-oral and extra-oral
examination, and there were no apparent swellings or lesions. Tooth # 14
was very sensitive to percussion and palpation, and the patient had pain
on biting. The tooth tested negative to hot and cold sensitivity. Teeth
# 13 and # 15 tested vital and asymptomatic.
Radiographic evaluation of tooth # 14 showed a completed
root canal therapy that appeared acceptable. Each of the apices had a puff
of cement extruded past the radiographic apex. A puff of cement can be
inevitable if the tooth is necrotic with no intact periodontal ligament
upon obturation. All three visible apices had periapical radiolucencies
evident, but without a pre-operative radiograph it is impossible to know
if the PARs are healing lesions or new lesions.
The diagnosis was a failed root canal therapy, and
the etiology could be related to a crack, incomplete cleaning and bacteria
removal, coronal leakage, or an accessory canal not treated.
The patient was anesthetized and # 14 was isolated
under a rubber dam. Upon access, the palatal, mesial buccal, and distal
buccal canals were located and examined. The canals were obturated with
gutta percha and appeared to be sealed coronally. Upon examination under
the microscope, there were no cracks or fractures evident and the tooth
appeared intact. Upon further examination, an MB2 was located mesially
lingually to the mesial buccal canal. (See Figure 1.) Instrumentation was
initiated on the MB2, and immediately the patient experienced discomfort.
There was no vital tissue remaining in the MB2, but the patient was experiencing
discomfort upon cleaning and shaping. The MB2 was a separate orifice and
apex from the MB. I decided to clean and shape the MB2 to a 25/08 file
and not retreat the other three canals at this time. Since the root canal
looked adequate, I wanted to start with the MB2 and if the symptoms were
relieved I would deduce the etiology of the pain was the accessory canal.
Calcium hydroxide was packed into the MB2 for one week. The patient called
the office three days later and stated that the pain was tapering off.
Maxillary First Molar Anatomy
The maxillary first molar can be a very challenging tooth to treat,
and has a very high endodontic failure rate. The maxillary first molar
has three individual roots, ligual/palatal, the mesialbuccal, and the distalbuccal.
These three root orifices usually form a tripod. The palatal canal is the
biggest and easiest to locate. The canal can be flat and ribbon-like; therefore,
careful debridement is necessary. The distalbuccal is usually straight,
conical, and has only one canal. The mesialbuccal root of the first maxillary
molar can be challenging due to the high incidence of MB2s.
Weine’s 1969 classic paper showed a 50 percent incidence
of MB2 canals. Pineda reported in 1973 that 42 percent of these roots manifested
two canals and two apical foramina. Kulid and Peters’s paper in 1990 concluded
that 95.2 percent of mesialbuccal roots had a second canal when the root
was sectioned. The reported incidence of MB2s varies, but one thing is
clear: MB2s are common; assume there are two canals until proven otherwise.
Locating MB2 Canals
The orifice for the MB2 usually lies lingual to the mesialbuccal canal
toward the palatal canal. The first thing a clinician should do is open
the access from a triangle-shaped to a rhomboid-shaped preparation. The
MB2 can be located mesial to the mesialbuccal canal. I got wonderful advice
from a teacher who told me to sweep mesially from the mesial buccal canal
toward the lingual. Fiber-optic illumination can aide in locating another
canal. Magnification is a large factor in the success of locating an MB2.
An ultrasonic tip can be used to sweep lingually from the mesialbuccal
canal, and this may open up the developmental groove.
Once a canal has been located, start with small
instruments first; it is very easy to block yourself out from these canals.
Oftentimes the MB2 orifice is angled, so the instrument will only enter
at a mesial/lingual angle in the beginning. Do not try to straighten the
orifice too early, because you do not want to ledge or block yourself out.
Very often the mesialbuccal canal and MB2 exit through the same foramina.
Second mesialbuccal canals can be very challenging
and frustrating for practioners, and I hope this helps!
September - October 2005
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FIGURE 1: an MB2 was located
mesially lingually to the mesial buccal canal.
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