Mesiobuccal root canal anatomy of Korean maxillary first and
second molars by cone-beam computed tomography
Jin-Hee Lee, DDS, MSD,aKee-Deog Kim, DDS, PhD,bJong-Ki Lee, DDS, MSD,c
Wonse Park, DDS, MSD,bJin Sun Jeong, DH,bYoon Lee, DDS, MSD,dYu Gu, MD,a
Seok-Woo Chang, DDS, PhD,eWon-Jun Son, DDS, PhD,aWoo-Cheol Lee, DDS, PhD,a
Seung-Ho Baek, DDS, PhD,aKwang-Shik Bae, DDS, PhD,aand Kee-Yeon Kum, DDS, PhD,a
Seoul, Wonju, and Changwon, Repubic of Korea
SEOUL NATIONAL UNIVERSITY, YONSEI UNIVERSITY, AND SUNGKYUNKWAN UNIVERSITY
Objective. The aim of this study was to investigate the types of canal configurations and the incidence of a second
mesiobuccal (MB2) canal in Korean maxillary molar mesiobuccal (MB) roots by analyzing cone-beam computed
tomographic (CBCT) images.
Study design. Three-dimensional CBCT images of 458 maxillary first molars and 467 second molars from 276 Korean
patients were analyzed to determine the incidence of an MB2 canal, the types of canal configurations, and the
correlations between the incidence of an MB2 canal and age, gender, and tooth position.
Results. The incidence of 2-canaled MB roots was 71.8% in first molars and 42.2% in second molars, with the most common
configurations being Weine types III and II. The frequency of an MB2 canal decreased with age in both molars (P ? .05).
Conclusions. Types III and II canal configurations were the most prevalent in the 2-canaled MB roots of Korean
maxillary molars. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2011;111:785-791)
The main objective of an endodontic treatment is to
complete a thorough mechanical and chemical cleansing
of the entire root canal system and its obturation with inert
filling materials.1Therefore, a better understanding of the
root canal system and its frequent variations is very im-
portant for successful endodontic therapy.2,3In the litera-
ture, the mesiobuccal (MB) root of maxillary permanent
molars has generated more research and clinical investi-
gation than any other root owing to its more complex root
canal anatomy and common variations, especially regard-
ing the prevalence of a second mesiobuccal (MB2) canal
and the types of canal configurations.2-8
Certain factors contribute to the wide variations re-
ported in the incidence of an MB2 canal in maxillary
molar MB roots. These include race, age, and gender of
the population studied, as well as the methods of re-
search.1,7-14The laboratory methods used to analyze
root canal morphology include sectioning,2clearing
computed tomography (MCT) techniques,18-20and
scanning electron microscopic observation of the pulpal
floor.21The techniques used in clinical studies include
inspection during endodontic treatment with or without
magnification tools,6radiography,22and reviews of pa-
tient records.5,23,24Currently, technologic advances
have been developed allowing a study that is accurate,
nondestructive, and feasible in vivo.
CBCT systems have been designed specifically to
produce undistorted 3-dimensional (3D) information on
the maxillofacial skeleton, as well as 3D images of the
Supported by the Technology Innovation Program Funded by the
Ministry of Knowledge Economy, Republic of Korea (no. 10031998:
Intelligent 3D dental diagnostic imaging system using CBCT).
The first two authors contributed equally to this work.
aDepartment of Conservative Dentistry, Dental Research Inst.,
School of Dentistry, Seoul National University, Seoul.
bDepartment of Advanced General Dentistry, College of Dentistry,
Yonsei University, Seoul.
cPrivate Practice, Beautiful Dental Clinic, Changwon.
dDepartment of Conservative Dentistry, Wonju College of Medicine,
Yonsei University, Wonju.
eDepartment of Conservative Dentistry, Institute of Oral Health Sci-
ence, Samsung Medical Center, School of Medicine, Sungkyunkwan
Received for publication Sep 26, 2010; returned for revision Nov 16,
2010; accepted for publication Nov 25, 2010.
1079-2104/$ - see front matter
© 2011 Mosby, Inc. All rights reserved.
Vol. 111 No. 6 June 2011
Editor: Larz S. Spångberg
teeth and their surrounding tissues.25These systems are
promising and are eminently more suitable than MCT
scans, which are limited to ex vivo applications only
and are not suitable for patient care. Currently, specific
endodontic applications of cone-beam computed to-
mography (CBCT) are being identified and, as the
technology becomes more prevalent in the field of
endodontics, will be able to provide valuable diagno-
ses25-27and morphologic analyses of the root canal
system.8,9,28-30Therefore, the aim of the present study
was to investigate the incidence of the MB2 canal in the
MB roots of the maxillary first and second molars in a
Korean population by gender, tooth position, and age
by using patients’ CBCT images taken for oral surgery
and implant placement. The root canal configurations
of the MB roots were also assessed.
MATERIAL AND METHODS
This study was approved by the Institutional Review
Board of Yonsei Dental Hospital, Yonsei University,
Seoul, Republic of Korea. Among the CBCT images
taken of patients who visited the Yonsei Dental Hos-
pital from August 2009 to July 2010 for implant sur-
gery and surgical removal of deeply impacted teeth
(including third molars and supernumerary teeth), high-
quality CBCT images from 276 patients (169 men and
107 women) were screened, and images of 458 maxil-
lary first and 467 second molars were evaluated retro-
spectively. The mean age of the patients was 37.7 years
of age, ranging from 18 to 76 years. For the maxillary
first molar, 200 of the subjects had bilateral molars, 58
had unilateral molars, and 18 had no first molar. For the
maxillary second molar, 206 of the subjects had bilat-
eral molars, 55 had unilateral molars, and 15 had no
second molar. Images of subjects who had maxillary
molars with a completely formed MB root and had not
had endodontic treatment, a post, or a crown were
selected for analysis.
The CBCT system used in this study was a Volux
system (Genoray, Seongnam, Republic of Korea), and
the scan settings were 85 kVp, 80 mA, 8.5 cm scan field
of view, and 0.167 mm3voxel size. Tomography sec-
tions of 0.167 mm in the axial, coronal, and sagittal
planes were created. The data were exported into DI-
COM file format.
3D Reconstruction and image analysis
Three-dimensional images of the maxillary first and
second molars were displayed using OnDemand3D
software (Cybermed, Seoul, Republic of Korea). The
presence of an MB2 canal and the types of canal
configurations present in the MB root were evaluated
using the OnDemand3D toolbar by carefully rolling
downward through the images from the pulp chamber
to the apex at the axial tomographic slices. Selecting
and moving the cursor on 1 image to change the center
of view altered the reconstructed slices in 3 orthogonal
planes (axial, coronal, and sagittal). These views were
used to examine the root canal system. All the images
were analyzed by 1 endodontist, and the assessment
was performed once a week for 2 weeks. The incidence
of an MB2 canal was evaluated and the canal config-
urations of the MB roots were classified into 5 catego-
ries. Types I to IV matched the Weine classification2as
follows: type I: a single root canal extending from the
pulp chamber to the apex; type II: separate root canals
leaving the pulp chamber and joining short of the apex
to form 1 canal; type III: 2 separate and distinct root
canals leaving the pulp chamber and exiting the root in
separate apical foramina; type IV: 1 canal leaving the
chamber and dividing into 2 separate and distinct canals
with separate apical foramina. Type V followed the
Yoshioka classification14and was defined as a root
canal configuration having ?2 canals.
The maxillary molars with a bilateral existence were
used for analysis of the bilateral occurrence of MB2
canals. The relationships between gender and tooth
position (right or left) and the incidence of an MB2
canal were assessed using Fisher exact test, and the
relationship between age and the incidence of an MB2
canal was assessed using Pearson ? correlation, with
statistical significance set at ? ? .05.
Analysis of CBCT images of the MB canal system in
the maxillary first molars showed that 70.5% of the MB
roots had 2 canals, 28.2% had a single canal, and 1.3%
had 3 canals (Table I). The type III canal configuration
Table I. Canal configurations and number and percentage of maxillary first and second molar mesiobuccal roots
Type IType II Type IIIType IVType V
No. of teeth (%)
Maxillary first molar
Maxillary second molar
Values within parentheses are percentages of total number of teeth examined.
Lee et al.
was the most prevalent in the MB roots of first molars
(Fig. 1). For maxillary second molars, 57.8% of the MB
roots had a single canal, 41.6% had 2 canals, and 0.6%
had 3 canals. In the 2-canaled MB roots, the type II
canal configuration was the most prevalent (Fig. 2).
Teeth with types II-V configurations of the MB root
were regarded as having an MB2 canal. In total, 71.8%
of the maxillary first molars and 42.2% of the maxillary
second molars had an MB2 canal.
Table II shows the numbers of MB2 canals and their
frequency in maxillary molars according to age. The
frequency of MB2 canals decreased with age in both
maxillary molars. For the relationship between age and
number of canals in the MB roots, Pearson ? correla-
tion produced a value of ? ? ?0.160 for maxillary first
molars and a value of ? ? ?0.260 for maxillary second
molars, which indicates an inverse correlation between
the age of the subject and the incidence of an MB2
canal (P ? .05).
Table III shows thattherewasasignificantrelationship
between gender and the incidence of an MB2 canal only
in maxillary second molars (48.7% in men and 30.8% in
women; P ? .05). Tooth position (right or left) was not
significantly correlated with the incidence of an MB2
canal in either the first or second molars (P ? .05).
However, 73.4% of the first molars and 52.0% of the
second molars with an MB2 canal occurred bilaterally.
The present study provides detailed anatomy of the
MB root canal of Korean maxillary molars based on a
retrospective analysis of CBCT images. Regarding the
types of canal configurations, the type III canal config-
uration was the most prevalent in the MB roots of first
molars. The high prevalence of the type III configura-
tion (2 canals with 2 separate foramina), which is a
typical mongoloid trait,9conforms to the findings of
earlier studies in Burmese, Indian, Japanese, Mexican,
and Thai populations.9-12,17This is in contrast to results
for Chinese8and caucasian1,13teeth, in which most of
the MB2 canals joined the main canal and exited
through 1 apical foramen (type II) in the 2-canaled MB
roots of first molars. These differences in canal config-
uration highlight the influence of ethnicity on the anat-
omy of the maxillary first molar root canal.
Unlike the type of canal configuration in first molars,
type II was the most common configuration in the
2-canaled MB roots of maxillary second molars. This is
in agreement with the results of Eskoz and Weine31and
Singh et al.32but differs from studies by Alavi et al.,11
Imura et al.,33and Neelakantan et al.,9who reported a
high prevalence of the type III configuration in MB
roots of second molars. Interestingly, many studies
have shown the incidence of the type III canal config-
uration in the 2-canaled MB roots of second molars to
Fig. 1. Cone-beam computerized tomography (CBCT) images of a right maxillary first molar with 2 canals in the mesiobuccal
(MB) root as viewed in the coronal, sagittal, and axial directions by using OnDemand3D software. A, Coronal view with the MB
root exhibiting type III canal configuration; B, sagittal view; C, axial view; D, 3-dimensional reconstruction image.
Volume 111, Number 6 Lee et al. 787
be lower than that in first molars.1,9-12,33The signifi-
cance of having the type II or III canal configuration
is important during endodontic treatment. In MB
roots with a type II canal anatomy, if the canals join
near the apex and one of the 2 canals has not been
cleaned properly, the chance of treatment failure will
increase. On the other hand, if a patient has an MB
root with type III canal configuration, clinicians
Fig. 2. CBCT images of a right maxillary second molar MB root with 2 canals as viewed in coronal, sagittal, and axial directions
by using OnDemand3D software. A, Coronal view with the MB root exhibiting type II canal configuration; B, sagittal view; C,
axial view; D, 3-dimensional reconstruction image. Abbreviations as in Fig. 1.
Table II. Number and frequency of additional canals in the mesiobuccal roots of the maxillary first and second
molars by age
10-20 20-30 30-40 40-5050-60
No. of teeth (%)
Maxillary first molar
Maxillary second molar
Values within parentheses are percentages of total number of teeth examined.
Table III. Number and frequency of additional canals in the mesiobuccal roots of the maxillary first and second
molars by gender and tooth position
Gender Tooth position
Male Female RightLeft
No. of teeth (%)
Maxillary first molar
(n ? 277)
(n ? 298)
(n ? 181)
(n ? 169)
(n ? 233)
(n ? 236)
(n ? 225)
(n ? 231)
Maxillary second molar
*Statistically significant (P ? .05).
Lee et al.
should keep trying techniques and devices necessary
to locate, debride, and fill both canals and the entire
root canal system to produce a more predictable and
favorable prognosis.33This is the reason why a better
understanding of internal morphology of root canal
system is essential for successful outcome of end-
Regarding the incidence of MB2 canals in maxil-
lary first molars, previous in vivo and in vitro studies
have shown the incidence to range from 56.9% to
96.0%.4-7,10-13,18,19,21,23,24,30,34,35The present CBCT
result (71.8%) was within the range reported in those
studies, which means that CBCT may be useful for
finding or confirming additional canals.29
Considering that ethnicity might result in differences
in tooth morphology,72 ex vivo morphology studies of
Korean populations were compared.18,35Both studies
examined the incidence of an MB2 canal in extracted
maxillary first molars by using MCT18and a sectioning
method after instrumentation and obturation.35The in-
cidences were reported to be 71.7% and 80.8%, respec-
tively, and the present CBCT result was within that
range. Furthermore, the most common canal configu-
ration in those 2 studies was the same (type III) as in the
For the MB roots of maxillary second molars in the
present study, the incidence of an MB2 canal (42.2%)
was similar to the results of some studies10,11,31,32but
higher than reported by others.1,6,9,36This variation in
the incidence of an MB2 canal can be attributed to
multiple factors, such as the study design (clinical/
laboratory), method of analysis, population studied, and
age of the sample (tooth).7-9,36
In the present study, a significant correlation with
the tooth position was not found in either molar, but
a significant gender difference was found regarding
the incidence of an MB2 canal in the maxillary
second molars. These results concur with those re-
ported by Fogel et al.34However, Zheng et al.8and
Neaverth et al.23reported that gender or tooth posi-
tion had little impact on the incidence of an MB2
Although tooth position had no influence on the
incidence of an MB2 canal in the present study, both
the first and second molars showed a high tendency for
the bilateral occurrence of an MB2 canal (73.4% for
first molars vs. 52.0% for second molars). This means
that if an MB2 canal exists on 1 side, clinicians must
consider the possibility of 2 canals in the contralateral
MB root and search for them when treating the con-
tralateral maxillary molars.
Recently, MCT has been used as a precise nonin-
vasive technique in experimental endodontology.20
However, the technique is time consuming and suit-
able only for laboratory use on a limited number of
teeth.19In contrast, CBCT technology provides the
clinician with an imaging modality that is capable of
providing a 3D representation of the maxillofacial
region and teeth with minimal distortion. Blattner et
al.30evaluated the ability of CBCT to detect an MB2
canal accurately in extracted maxillary first and sec-
ond molars. They demonstrated that CBCT scanning
accurately identified the presence or absence of an
MB2 canal in 78.9% of samples and was a reliable
method for detecting an MB2 canal compared with
sectioning of the specimens. Matherne et al.37com-
pared the ability of CBCT to identify root canal
systems with images obtained by charge-coupled de-
vice and photostimulable phosphor plate digital ra-
diography in vitro, concluding that CBCT images
always identified a larger number of root canals than
did digital images. They concluded from their results
that CBCT is an accurate and effective tool for
examining the morphology of the root canal.
The present study clearly showed that age had some
influence on the incidence of an MB2 canal in maxil-
lary MB roots. The maxillary first molars in subjects
30-40 years old and the maxillary second molars in
subjects 10-20 years old showed the highest frequency
of an MB2 canal. Furthermore, an inverse correlation
was found between age and frequency of an MB2 canal
in both maxillary molars. With age, the time the tooth
had been exposed to outside irritation, such as caries,
trauma, and canal calcification caused by restorative
procedures, also increased, and the probability of locat-
ing an MB2 canal decreased. This was also confirmed
by the results of Neaverth et al.23and Thomas et al.13
We therefore suggest that more attention be directed
toward searching for and locating MB2 canals in the
MB roots of maxillary molars, especially in those pa-
tients ?40 years old. In this regard, the incidence of an
MB2 canal may have been underestimated in the pres-
ent study. Because older subjects have more calcified
canals and the diameter(s) of the additional canal(s) are
smaller than the diameter of the MB1 canal,38it would
be too difficult to detect the additional canal(s) clearly
in the CBCT images.
Although many earlier studies, as well as the present
study, clearly demonstrated that CBCT systems might
be a valuable tool for morphologic analysis of the root
canal system,8,9,28-30,37,39,40CBCT cannot be routinely
used in all cases of nonsurgical endodontic treatment. It
is worth remembering that CBCT still uses ionizing
radiation and is not without risk. It is essential that the
patient’s radiation exposure be kept as low as reason-
ably achievable41and that evidence-based selection
criteria for CBCT be developed. Therefore, endodontic
cases should be judged individually, and until further
Volume 111, Number 6 Lee et al. 789
evidence is available, CBCT should be considered only
when it has been determined that conventional radio-
graphic view(s) are yielding limited information and
that further radiographic details are required for diag-
nosis and treatment planning.26-29,42,43
In conclusion, the present retrospective study showed
that the Korean population has a higher prevalence of type
III and II canal configurations in 2-canaled MB roots of
maxillary molars and that the incidence of 2 canals in MB
roots was higher in first molars than in second molars.
These anatomic variations of MB roots may exist in
ethnically different populations and should be considered
during surgical or nonsurgical endodontic procedures of
the permanent maxillary molars.
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Dr. Kee-Yeon Kum
25-9 Jongro-Gu Yungun-dong
Department of Conservative Dentistry
Dental Research Inst. and BK 21 Program
Sch. of Dentistry
Seoul National University
Republic of Korea
Volume 111, Number 6Lee et al. 791