Three-dimensional analysis of maxillary first molar mesiobuccalroot canal configuration and curvature usingmicro–computed tomographyJong-Wook Park, DDS, PhD,a Jong-Ki Lee, DDS, MSD,b Byung-Hyun Ha, PhD,c

Jeong-Ho Choi, DDS, PhD,d Hiran Perinpanayagam, DDS, PhD,e Seoul and Busan, SouthKorea; and London, OntarioSEOUL NATIONAL UNIVERSITY, PUSAN NATIONAL UNIVERSITY, SMILE FUTURE ORTHODONTICCLINIC, AND UNIVERSITY OF WESTERN ONTARIO

Objective. The complex anatomic configuration of the maxillary first molar mesiobuccal (MB) root canal system hasbeen the subject of several studies. The purpose of this investigation was to analyze the 3-dimensional (3D)characteristics of the maxillary first molar MB canal system using micro–computed tomography (microCT).Study design. Extracted maxillary first molars (46) were scanned by microCT and their canals reconstructed by 3Dmodeling software.Results. In these MB roots, nearly two-thirds (65.2%) had 2 canals, fewer than one-third (28.3%) had only 1 canal,and a few (6.5%) had 3 canals. The most common root canal configuration was 2 distinct canals (type III: 37.0%),followed by 1 single canal (type I: 28.3%), 2 canals that joined together (type II: 17.4%), 1 canal that split into 2 (typeIV: 10.9%), and 3 canals (type V: 6.5%).Conclusion. MicroCT provided an in-depth analysis of canal configurations, as well as length, curvature, and location

of calcified segments. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:437-442)

A thorough comprehension of the intricate 3-dimen-sional (3D) configuration of a root canal system isessential for the provision of successful endodontictherapy. Therefore the complex anatomic configurationof the maxillary first molar mesiobuccal (MB) rootcanal system has long been the subject of considerablescrutiny. This complicated and variable canal anatomyhas been studied by a variety of techniques.1 In vivoclinical studies have included retrospective evaluationsof patient records, radiographic assessments, and clin-ical examinations during endodontic treatment, bothwith and without the aid of magnification. In vitrolaboratory studies have used extracted teeth and haveincluded endodontic access, examination, radiography,scanning electron microscopy, grinding and sectioning,as well as numerous clearing studies using decalcifica-tion with India ink and other dyes.

All of this literature pertaining to maxillary first

aDepartment of Oral Anatomy, Seoul National University.bDepartment of Oral Pathology, Seoul National University.cDepartment of Industrial Engineering, Pusan National University.dSmile Future Orthodontic Clinic, Seoul, South Korea.eSchulich School of Medicine & Dentistry, University of WesternOntario, London, Canada.Received for publication Dec 3, 2008; returned for revision Jan 9,2009; accepted for publication Jan 10, 2009.1079-2104/$ - see front matter© 2009 Published by Mosby, Inc.

doi:10.1016/j.tripleo.2009.01.022

molar anatomy was recently reviewed by Cleghorn etal.1 They carefully reviewed 34 clinical and laboratorystudies that reported on the MB root canal morphologyof 8,399 maxillary first molars, and showed that therewas considerable variability between the studies. Aweighted average from all of the studies showed thatthere were �2 (multiple) MB canals in 57% of the teethand only a single canal in 43%. There was a singleapical foramen in 62% of the MB roots, and �2 sepa-rate foramina in 38%. Furthermore, the in vitro labo-ratory studies on extracted teeth were more likely toidentify a second MB canal (61%) than the in vivoclinical investigations (55%).

In contrast to these older techniques, more recentresearch has used micro–computed tomography (mi-croCT) coupled with mathematical modeling to per-form a detailed 3D analysis of the root canal system. In1995, Nielsen et al.2 found that microCT accuratelyreproduced internal and external tooth morphologywithout tooth destruction and demonstrated surface andvolume changes after instrumentation and obturation inextracted maxillary molars. Similarly in 1999, Bjorndalet al.3 used microCT to compare the external rootsurface with the internal root canal system in maxillarymolars. Also in 1999, Rhodes et al.4 used microCT tocalculate the internal and external surface areas ofextracted mandibular molar roots and found that theycorrelated closely with the calculations made from dig-

ital video images. Similarly in 2000, Peters et al.5

437

OOOOE438 Park et al. September 2009

showed that high-resolution microCT accurately repro-duced the root canal geometry of extracted maxillarymolars. Additionally in 2001, Bergmans et al.6 usedmicroCT with mathematical modeling to measure thechanges in volume and transportation that occur withinstrumentation in 1 extracted mandibular molar. Morerecently in 2004, Fan et al.7,8 used microCT to study theintricate anatomic features of C-shaped mandibular sec-ond molar roots.

One of the anatomic characteristics of a root canalsystem which has an important influence on endodontictherapy is canal curvature. The amount of curvature ina root canal affects the access for instrumentation andthe risk of instrument separation. Canal curvature wasinitially measured from 2-dimensional radiographs.9-16

Schäfer et al.15 measured canal curvature in 50 maxil-lary first molars on plain radiographs. However, recentstudies have utilized microCT with mathematical mod-eling to more comprehensively analyze the 3D curva-ture in a root canal system.5,17 In 2000, Peters et al.5

measured the curvature in 12 maxillary molar canalsusing microCT. In 2006, we performed a more com-prehensive and 3D analysis of the canal curvatures in46 maxillary first molars using microCT and mathe-matical modeling with customized software.17 The im-age reconstruction that we obtained from microCTanalysis revealed complex anatomic configurations inthe MB canal and pronounced curvature.

Having successfully applied microCT and mathe-matical modeling to analyze the 3D curvature of max-illary first molar root canals, we sought to use thesetechniques to study the complex configuration and cur-vature of the MB canal system. Therefore, the purposeof the present study was to analyze the 3D morphologiccharacteristics of the maxillary first molar MB canalsystem using microCT. The first objective was to iden-tify the different types of canal configurations and tomeasure their lengths. The second objective was tomeasure root canal curvature in each of the differenttypes of configurations and within each trisection of thecanal system. The third objective was to identify cal-cified segments within the canals.

MATERIALS AND METHODS

Sample preparationAs we previously described,17 a total of 46 intact

maxillary molar teeth which had been extracted fromKorean adults were collected from local dental practi-tioners in South Korea. The external surfaces of theteeth were carefully cleaned of calculus and soft tissueattachments with an ultrasonic scaler and sodium hy-

pochlorite (5.25%).

Micro–computed tomographyAs we previously described,17 the teeth were scanned

by microCT (SkyScan 1072; SkyScan, Aartselaar, Bel-gium) and images acquired from 502 slices of eachindividual tooth. Each image had a resolution of 1,024� 1,024 pixels and a voxel size of 19.5 � 19.5 � 39.0�m. From these images, a 3D model of the root canalsystem was constructed with 3D modeling software(V-Works 4.0; Cybermed, Seoul, Korea) on a personalcomputer (Pentium 4, 2.40 GHz CPU, 2 Gbyte RAM,Windows 2000).

Classification of canal configurationThe reconstructed 3D model of the MB root canal

system in each maxillary first molar was carefully ex-amined. Their configuration was determined and eachMB canal system was classified into 1 of 5 categories(types I, II, III, IV, and V). Types I to IV followedWeine et al.’s classification,18 and type V were basedon Yoshioka et al.’s system, as previously described.19

According to this classification system, type V config-urations had �2 main canals, and the additional canalhad to branch off from the main canal at a point thatwas �3 mm from the apex, so as not to be classified asan accessory canal.

Root canal curvatureThe central axis was determined for each canal and

its curvature calculated as previously described.17 Ineach canal, 5-15 image slices were selected to ade-quately span the entire length. On each slice, major andminor axes were plotted manually, and their points ofintersection were connected to create a central axis.This central axis was defined as a cubic B-spline curveusing the V-Works software. Kappa software devel-oped specifically for the study imported the central axisof each canal from the V-Works program and thenmeasured the radius of curvature of the tangential circleat each point along the central axis. Then the radius ofcurvature of the tangential circle was inverted to pro-vide a measure of the actual curvature. In addition, theKappa software was used to calculate the mean curva-ture of each trisection (coronal, middle, and apicalthirds).

RESULTSCanal configuration

MicroCT analyses of the MB canal system in 46maxillary first molar teeth showed that 13 (28%) had asingle root canal (type I) and 33 (72%) had multiplecanals (types II, III, IV, and V) (Table I). Of the teethwith multiple canal systems, 30 (65%) had 2 canals(types II, III, and IV) and 3 (7%) had 3 canals (type V).

Of the teeth with 2 canals, 17 (37%) had 2 distinct

10.3

OOOOEVolume 108, Number 3 Park et al. 439

canals (type III), 8 (17%) had a 2-to-1 configuration(type II), and 5 (11%) had a 1-to-2 configuration (typeIV).

Each of the 46 maxillary first molar teeth had anidentifiable MB1 canal (n � 46), and 33 of the teethhad an MB2 canal system, of which 3 teeth had anadditional third canal (type V). These 33 MB2 and 3MB3 canal systems were combined (n � 36) for thepurpose of statistical analysis.

Canal lengthThe mean length of the MB1 canal was 9.8 mm,

which was 0.6 mm longer than the 9.2 mm length of theMB2 canal (Table I). When there was only 1 canal(type I), the single MB1 canal was longer, with a meanlength of 10.1 mm. When there were 2 distinct canals(type III), the MB1 canal had a mean length of 9.8 mm,which was 0.6 mm longer than the 9.2 mm length of theMB2 canal. Similarly, when there was a 1-to-2 config-uration (type IV), the MB1 canal had a mean length of9.7 mm, which was 0.6 mm longer than the 9.1 mmlength of the MB2 canal. However, when there was a2-to-1 configuration (type II), the MB1 canal had amean length of 9.7 mm, which was 0.6 mm shorter thanthe 10.3 mm length of the MB2 canal. In addition,when there were 3 canal systems, the MB1 canal had amean length of 9.6 mm, which was nearly 2 mm longerthan the other 2 canals.

Canal curvatureThe MB canals had a considerable amount of curva-

ture, as we have previously reported.17 In the MB1canals the largest amount of curvature was within theapical third. There was a moderate amount of curvaturein the coronal third and the least amount of curvaturewithin the middle (Table II). The MB2 canals hadconsiderably more curvature overall and within eachtrisection than the MB1 canals. The MB2 canals hadconsiderably more curvature within the coronal, mid-dle, and apical thirds than the MB1 canals. In the MB2canals the largest amount of curvature was also withinthe apical third, but this was followed very closely by alarge amount of curvature in the coronal third and amoderate amount of curvature within the middle. Fur-

Table I. Mesiobuccal (MB) canal configuration and leOverall I

No. of teeth 46 (100.0%) 13 (28.3%)Length, mm

MB1 (n � 46) 9.8 � 1.1 10.1 � 1.1MB2 (n � 36) 9.2 � 1.3 —

thermore, in the MB2 the middle third with the least

amount of curvature still had as much curvature as theapical third that had the most curvature in the MB1.

Configuration and curvatureIn the MB1 canal, overall curvature was similar

when there was a type I, II, III, or V configuration, andlarger when there was a type IV (1-to-2) canal system(Table III). However in the MB2 canal, overall curva-ture varied considerably with canal configuration. Inthe MB2, curvature increased sequentially in type II,IV, III, and V configurations. The MB2 canals in a typeII (2-to-1) configuration had the least amount of curva-ture of the MB2 canals, yet they had slightly morecurvature than the MB1 canals in a type IV (1-to-2)configuration which had the most curvature of the MB1canals. Accordingly, the MB2 canals with a type V (3canals) configuration had pronounced curvature.

Calcified segmentsThe microCT analysis of these 46 maxillary first

molar teeth demonstrated the presence of several cal-cified segments within the MB canal system (Fig. 1).There were 18 calcified segments that were identified inthe MB2 canals, of which �3 times as many werelocated in the coronal third (14) than in the apical third(4) (Table IV). In contrast, there were only 2 calcifiedsegments that were found in the MB1 canals, of which1 was located in the coronal third and 1 in the apical.The mean length of the calcified segments was close to1 mm in the MB1 (0.9 mm) and in the MB2 (1.1 mm)canals.

Comparative analysisIn this microCT study of the MB canal system in 46

maxillary first molars, there were 13 teeth (28.3%)which had only a single canal both within the MB rootand at the apex (type I; Fig. 2). The remaining 33 MBroots (71.7%) had �2 canal systems. Of the MB rootswith multiple canals, 8 had a 2-to-1 type II configura-tion, so that in total (types I and II) there were 21 roots(45.7%) which had only a single apical foramen. Theother 25 teeth (54.3%) had multiple canals both withinthe root and at the apex (types III, IV, and V).

In comparison, the review by Cleghorn et al.1 of 21

II III IV V

7.4%) 17 (37.0%) 5 (10.9%) 3 (6.5%)

� 1.1 9.8 � 1.0 9.7 � 1.6 9.6 � 0.6� 1.1 9.2 � 1.2 9.1 � 0.8 7.9 � 0.8

ngth

8 (1

9.7

laboratory studies encompassing 3,119 maxillary first

(3.3 � 1

0.36 �

OOOOE440 Park et al. September 2009

molars found that 1,233 MB roots (39.5%) had a singlecanal and 1,886 (60.5%) had multiple canal systems(Table V). Of these, 16 laboratory studies encompass-ing 2,033 teeth had also examined the MB apex. Therewere 1,350 MB roots (66.4%) with a single canal at theapex and 683 (33.6%) with multiple apical foramina.

Cleghorn et al. also reviewed 13 clinical studies thatincluded 5,280 maxillary first molars, of which 2,387(45.2%) had a single canal in the MB root and 2,893(54.7%) had multiple canal systems. Of these, 6 clinicalstudies on 2,072 teeth had also looked for apical exits

Table II. Mean mesiobuccal (MB) canal curvature (mCanal Overall Corona

MB1 (n � 46) 0.22 � 0.06 (5.0 � 1.5) 0.20 � 0.09MB2 (n � 36) 0.34 � 0.13 (3.4 � 1.4) 0.37 � 0.17

Table III. Mesiobuccal (MB) canal configuration, curvCanal I II

MB1 (n � 46) 0.21 � 0.07 (5.4 � 1.8) 0.22 � 0.04 (4.8 � 0.9)MB2 (n � 36) — 0.27 � 0.08 (4.0 � 1.5)

Fig. 1. The 3-dimensional root canal system in the mesio-buccal (MB) root of each maxillary first molar was recon-structed with micro–computed tomography and mathematicalmodeling. In the MB2 canal, calcified segments were fre-quently identified within the coronal (A) and the apical (B)portions of the canal.

from the MB root. There were 1,179 MB roots (56.9%)

with a single canal at the apex and 893 (43.1%) withmultiple apical exits.

DISCUSSIONIn the present study, the complex 3D configuration

and curvature of the MB root canal system was exam-ined in 46 maxillary first molars using microCT andmathematical modeling. In this analysis, nearly two-thirds (65.2%) of the teeth had 2 MB canals, a littleover one-fourth (28.3%) had only 1 canal, and a smallnumber (6.5%) had 3 canals. The most common ana-tomic configuration was 2 distinct MB canals in a typeIII pattern (37.0%). The next most common appearancewas a single canal in a simple type I configuration(28.3%). A less common arrangement was 2 MB canalsthat joined together in a 2-to-1, or type II, configuration(17.4%). Even less common was 1 MB canal that splitinto 2 in a 1-to-2, or type IV, configuration (10.9%),and least common were 3 canals in a type V configu-ration (6.5%).

In comparison, a recent clearing study by Yoshiokaet al..20 on 98 extracted maxillary first molars found asimilar proportion of MB roots with 2 canals (66%),slightly more with only 1 canal (33%), and much fewerwith 3 canals (1%) They had removed dentin (trough-ing) to locate additional MB canals, and thereby de-stroyed coronal canal anatomy, so that they were un-able to distinguish between type III and IV canals. Yetthey found a higher proportion of type II canals (36%)and a lower number in the type III and IV category

and radius of curvature (mm, in parentheses)Middle third Apical third

.6) 0.16 � 0.05 (6.7 � 2.4) 0.28 � 0.13 (4.5 � 2.5)

.6) 0.28 � 0.14 (4.5 � 2.2) 0.38 � 0.21 (3.9 � 3.2)

(mm�1), and radius of curvature (mm, in parentheses)III IV V

0.07 (5.2 � 1.5) 0.26 � 0.04 (4.0 � 0.8) 0.21 � 0.06 (4.9 � 1.2)0.14 (3.1 � 0.9) 0.31 � 0.10 (3.5 � 1.1) 0.42 � 0.15 (3.1 � 2.5)

Table IV. Calcified mesiobuccal (MB) canal segment,length and location

Canal LengthCoronal

thirdMiddlethird

Apicalthird

MB1 (n � 46) 0.9 � 0.1 mm 1 (2.2%) 0 1 (2.2%)MB2 (n � 36) 1.1 � 0.5 mm 14 (38.9%) 0 4 (11.1%)

m�1)l third

(6.2 � 3

ature

0.21 �

(31%) than in we did in our study.

OOOOEVolume 108, Number 3 Park et al. 441

An earlier clearing study by Ibarrola et al.21 exam-ined 87 extracted maxillary first molars which had beenused by dental students in an endodontic techniqueslaboratory. They found that the most common arrange-ment was a type III configuration (36%), which wassimilar to our study. Their proportion of type I (23%)and type IV (9%) were also similar to our study. How-ever, their proportion of type II canals (32%) was muchhigher than in ours, and they did not identify any thirdcanals (type V) using their technique.

Likewise, others have reported a similar proportionof type III canals, despite a wide variation in the num-ber assigned to other configurations. In an in vitroexamination of 293 extracted maxillary first molarsfrom Japanese patients, Weine et al.18 reported a sim-ilar number (30.4%) with a type III configuration, al-though they had assigned a much larger proportion(42%) to type II and a smaller proportion to type IV(3.4%) than in our study. In a clinical investigation on

Fig. 2. The proportion of MB roots with single (type I) andmultiple (types II, III, IV, and V) canals and the proportionwith single (types I and II) and multiple (types III, IV, and V)apical foramina were compared. These results from thepresent study (Current MicroCT) were compared with thelaboratory and clinical studies reported by Cleghorn et al. in2006.1

Table V. Clinical and laboratory studies on the mesio-buccal canal system

Canal system Canals at apex

Single Multiple 2-to-1 Multiple

Current microCT analysis 28.3% 71.7% 45.7% 54.3%Review of laboratory studies* 39.5% 60.5% 66.4% 33.6%Review of clinical studies* 45.2% 54.7% 56.9% 43.1%

*Cleghorn et al., 2006.1

1,096 conventionally treated maxillary first molars,

Stropko found a similar proportion with the type IIIconfiguration.22

This similarity in the reporting of type III canals,despite a wide variation in the numbers that are as-signed to the other configurations, is noteworthy. Thereason might be attributed to the complexity of the MBroot canal system and its interpretation and classifica-tion. In the type III configuration there are 2 distinctorifices which each run through into separate apicalexits. Therefore, this configuration can be more readilyidentified, even with the simple insertion of files andthe taking of a radiograph. However, with complexanatomic configurations, cross-sectioned slices of a ca-nal can be difficult to assign to the type I or type IIpattern. In these cases, a complete 3D analysis usingmicroCT technology is essential for an appropriateclassification of the canal system.

In addition to accurately classifying the canal con-figuration, these microCT reconstructions allowed us tolocate the most pronounced 3D curvatures and to iden-tify calcified segments within the canals. We found thatthere was a combination of pronounced curvatures anda high incidence of calcified segments within the coro-nal portion of MB2 canals. These features have pro-vided a major hindrance to the location and negotiationof MB2 canals. Accordingly, earlier studies utilizedspecial techniques to overcome these obstacles. Forexample, Yoshioka et al.20 discovered many additionalMB2 canals after removing coronal dentin (troughing).They also reported that many of the MB2 canals hadabrupt curvatures within their coronal portion and thatseveral MB2 canals were undetected owing to calcifi-cation.

Therefore, the present microCT study has provided athorough and comprehensive analysis of the MB canalanatomy in maxillary first molar teeth. It has confirmedthe high incidence of additional canal spaces within theMB root, and it has accurately portrayed its complexanatomic configuration through quantitative means.These 3D reconstructions may someday aid in ourprovision of endodontic therapy and abet our ongoingstudy of canal anatomy.

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Reprint requests:

Dr. Hiran PerinpanayagamAssociate Professor in DentistrySchulich School of Medicine & DentistryUniversity of Western Ontario DSB 0079London, ON N6A 5C1Canada

hiran.perinpanayagam@schulich.uwo.ca