Introduction
The ultimate goal of root canal treatment is a thorough cleaning and shaping of all pulp spaces and the complete obturation of these spaces with an
inert filling material.(1) Therefore, the knowledge of root canal anatomy of each tooth is crucial in order to reach this goal. (2)
Sometimes a root canal can go untreated because the clinician fails to detect it. The inability to locate extra canals will result in failure of
endodontic treatment.
Diagnostic measures are of great help in locating root canal orifices. These measures include obtaining and careful interpretation of multiple
pre-treatment radiographs, adequate access and modification of the outline of the access cavity, exploration of the tooth's interior and exterior and
examination of the pulp chamber floor with appropriate magnification and illumination.(1,3)
The internal anatomy of the human teeth has been studied by many investigators using different techniques such as sectioning of teeth, (4,5) clearing techniques,(6,7,8) radiography,(9,10) examination under operating
microscope,(11) examination with a scanning electron microscope(12) and cone-beam computed tomography
techniques.(13,14) Locating the position and number of root canals can be difficult especially when the tooth being treated is malposed, heavily restored, or calcified. (3)
The maxillary first molar usually has three roots with a single canal located in each root except with the mesiobuccal root in which a second canal may
be present. In vitro studies indicated this second mesiobuccal canal (Mb2) in 25%-95.2 % of extracted teeth. (4,12,15) While in vivo studies have produced much lower figures 3.3%-73.2%.(16,17) This
apparently reflects the difficulty in locating the extra canals in clinical endodontic practice if unaided by the use of magnifying aids such as
surgical loupes or a dental operating microscope.(18)
The mandibular first molar seems to be the tooth that most often requires root canal treatment.(1) The tooth usually has two roots
(mesial and distal) with two canals in the mesial root and one canal in the distal.(1) The incidence of four
canals in the mandibular first molar has been reported in the literature between 22%-59%.(19, 20)
The study of root canal anatomy has endodontic as well as anthropological significance.(21,22) It is well known that tooth anatomy
varies according to racial origin.(10,23) Therefore it is very important to be familiar with variations in tooth anatomy and
characteristic features in various racial groups since such knowledge can aid in location and negotiation of canals, as well as their subsequent
management.
The aim of this study was to clinically investigate the incidence of a fourth canal in maxillary and mandibular first molars in a group of Jordanians
in routine endodontic practice without using any magnification or special lighting conditions.
Methods
Three hundred ninety nine patients were referred to the conservative clinic at Princess Aysha Bint Al-Hussein Medical Complex for endodontic treatment
of maxillary or mandibular first molars from November 2008 till May 2009. Preoperative radiographs were taken for evaluation (root morphology, number
of canals and periapical status).
The teeth that were included in the study were those teeth that required nonsurgical endodontic treatment. The
included teeth were free of root resorption, had no calcifications or open apices. No retreatment cases were included in the study.
The endodontic procedures undertaken were as follows: Local anesthesia (Ubistesin Forte/ 3M ESPE, Seefeld-Germany) was administered. Under rubber dam
isolation an access cavity was prepared with sterile high and low speed burs with water coolant.
In maxillary first molars the outline of the access
cavity was modified to a rhomboidal shape to improve visibility of the second mesiobuccal canal orifice while in mandibular first molars, the access
cavity outline was modified to a more rectangular shape to expose the location of the second distal canal orifice.
After the contents of the pulp
chamber were removed, a sharp endodontic explorer was used to explore the developmental grooves carefully to locate the orifices of the canals. Copious
amounts of 2.5% sodium hypochlorite irrigation were used.
The MB2 canal was considered present only when the canal could be traced and enlarged to a length of at least 1/2 or more of the main mesiobuccal
canal. Pulp tissue was extirpated using barbed broaches (Nerve Broaches/ Alfred Becht-GmbH,Germany) or H-Files (Mani inc, Japan) the canals were flared
with gates glidden drills number 2,3 and 4 (Mani inc, Japan). Periapical radiographs with different angles were taken for evaluation of the number of
root canals and for confirmation of the working length after inserting size 15,20 or 25 K files (Mani inc, Japan) in the canals.
The teeth included were both clinically and radiographically examined by two specialist with more than 10 years of experience for the presence of a
second mesiobuccal canal in maxillary first molars and a second distal canal in mandibular first molars and the incidence of a fourth canal in
maxillary and mandibular first molars was calculated.
Results
A total of 399 patients (216 females and 183 males) were treated at the conservative clinic at Princess Aysha Bint Al-Hussein Medical Complex from
November 2008 till May 2009. The mean age of patients was 28.23 years, ranging from 13.0 to 66.0 years An overall of 399 teeth were treated endodontically. 195 (48.9%) were maxillary first molars while 204 (51.1%) were mandibular first molars.
Forty five teeth (23.1%) out of the 195 treated maxillary first molars had a second canal (Mb2) in the mesiobuccal root. All the distobuccal and
palatal roots had a single canal. The 195 patients who had their maxillary first molars treated endodontically were 93 (47.7%) females and 102 (52.3%)
males. Out of the 93 females 21(22.6%) had a 4th canal, whereas for the 102 males 24 (23.5%) had a fourth canal (Table I).
Regarding the mandibular first molar out of the 204 teeth, 99 teeth (48.5%) had four canals; two mesial and two distal canals. Of those 204 patients,
123(60.3%) were females and 81(39.7%) were males. The incidence of fourth canal was 51.2% in females and 44.4% in males (Table I).
Discussion
The cause of most endodontic failures is inadequate biomechanical instrumentation of root canal system.(3) This can result from
inadequate knowledge of root canal anatomy, because one can never know before treatment how many root canals are in a tooth. Together with diagnosis
and treatment planning, knowledge of common root canal morphology and its frequent variations is a basic requirement for endodontic success. (1) This emphasizes the belief that it is easier to recognize a feature if one is already prepared to see it.
There is a lack of consistency in the reported incidence of 2nd mesiobuccal canal (Mb2) in maxillary 1st molars in the
literature. The differences may be due to the study design (clinical versus laboratory), method of canal identification (radiographic examination, root sectioning, canal staining and root clearing, examination
with SEM or cone-beam computed tomography techniques) or true differences in the sample under investigation (racial variation). Table II shows the
variation in the incidence of Mb2 in different studies with different variations.
In clinical practice, the location of the Mb2 in the maxillary 1st molar is always challenging. This canal usually originates lingual and
slightly distal to the main Mb canal, but occasionally shares the same orifice with it.(4,12) The canal is not always visible after
access cavity preparation as it is often smaller and covered by calcifications.(4) In the present study Mb2 canal in the maxillary 1 st molar was located in 23.08% the result is in agreement with a study done on Saudi population by Al-Nazhan, who reported an incidence of
23.3%.(30)
It is also within the range that has been reported by most investigators in clinical studies.(16,17)
Comparing to an in vitro study that has been done by Khraisat and Smadi, on Jordanian population the incidence is much lower. (28) This difference may be due to the study design because the incidence of additional canals in the Mb root of maxillary first
molar has produced much higher figures in in vitro studies.(4,12,15)
Investigators who have attempted both laboratory and clinical methods have reported a higher chance of finding two canals in Mb roots in the
laboratory, highlighting the difficulty of finding the Mb2 canal clinically.(5,7,16) Abiodun-Solanke et al.
recorded the incidence of additional canal in maxillary first molar of Nigerian population and found in the laboratory phase of the study that 23% of
the sectioned teeth had Mb2 while for the clinical phase of the study they found that only 3.3% of the treated teeth had Mb2.(16) Limited access and visibility and non-
constant location of the second canal as well as the risk of perforation may explain the lower incidence of having two canals in the mesial root of
maxillary molars in clinical practice when compared with laboratory studies. Clinically, finding the Mb2 canal can be improved by modification of the
outline of the access cavity, and by widening and deepening the grove running palatally from the major mesiobuccal canal orifices.
The use of dental loupes and dental operating microscope (DOM) provides the clinician with superior lighting and magnification improving the ability to
treat cases and finding extra canals.(31) Buhrely et al. reported the incidence of a Mb2 canal when the teeth examined using
traditional techniques to be 17.2% but with the use of operating microscope as a magnifying aid the incidence increased to 62.5%.(31)
The clinical studies adapting the surgical microscope in conjunction with a modified access cavity have reported a higher incidence of Mb2
canals.(5,17,24) In this study no magnification aids were used due to inavailability, this may contributed to the low incidence of
Mb2 in maxillary first molars due to the possibility of missing some extra canals.
All the distobuccal and palatal roots of teeth received endodontic
treatment had a single canal. This is similar to the findings in studies done by Wasti et al. and Alavi et al.(8,25)
However, other researchers reported contrasting results. Maggiore et al. reported cases of maxillary first molars with six canals: two in each
root.(2)
Baratto- filho et al.and Shetty et al. reported cases of maxillary first molars with two palatal roots. (32,33) Kottor et al. reported a case with three roots and seven canals (three canals in the mesiobuccal root, two canals in
the distobuccal root and two canals in the palatal root).(34)
Regarding the mandibular first molar, in this study 48.5% of the teeth had four canals two mesial and two distal canals. The result is in agreement with the findings of Al-Qudah and Awawdeh, who
reported that 47% of their specimens from Jordanian population had 4 canals.(35) It is also comparable to other studies done by Wasti et al., Pattanshetti et al. and Chen et al.(25,36,37) Table III shows some of the studies on the
incidence of four canals in the first mandibular molar in different ethnic groups.
Some researchers reported unusual variation in the number of canals in mandibular first molars. Berna and Badanelli reported two cases where three
separate canals existed in the mesial and distal roots of the first mandibular molar.(40)
In clinical practice, the important factors which help in locating and treating extra canals are the clinician’s awareness of their presence and the
allocation of sufficient time and effort to locate and treat these canals using all the available useful equipments.
Conclusion
A fourth canal was found in about 23% of maxillary first molars and in about 49% of mandibular first molars. There is no consistency in the incidence of extra canals. This may be due many variations including: the study design, the method of canal identification and the racial
variations.
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