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omplicated Root Canal Morphology of Mandibular Firstremolar in a Chinese Population Using the Cross Sectionethod

zu-Yi Lu, DDS,* Shue-Fen Yang, DDS, MS,†‡ and Sheng-Fang Pai, DDS†‡

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bstracthe purpose of this study was to assess the canalnatomy and morphology of mandibular first premolars

n a Chinese population. Eighty-two extracted mandib-lar first premolars with intact roots were collected andtored in a glutaraldehyde solution. The teeth werembedded in clear resin and the root length was mea-ured. The roots were resected perpendicular to theong axis at 3, 6, 9, and 12 mm from the apex. Theesected root surfaces were polished, rinsed, dried, andtained with methylene blue. Digital photographs of theross-sectional root surfaces were made at 24X. Thencidence of multiple canals and varied morphologyas determined by two independent examiners. The

esults indicated that 54% of the mandibular first pre-olars demonstrated a single canal. Twenty-two per-

ent contained two canals and 18% percent had C-haped configuration. The C-shaped root canalccurred predominantly in the 3 and 6 mm sectionsith one or two canals coronally. A unique finding was

he circumferential canal (apical delta), which was char-cterized by a single canal splitting into 3 or 4 canals.he incidence of circumferential canal was 6% andccurred only in the apical 3 mm cross-sections. Iden-ification of this unique apical canal configuration andhe high incidence of multiple canals in mandibular firstremolars may explain endodontic treatment failure inhis tooth group. (J Endod 2006;32:932–936)

ey Wordsircumferential canal, C-shaped canal, mandibular firstremolar, root canal morphology

From the *Department of Dentistry, Mackay Memorialospital, Taiwan, Republic of China; †Department of Dentistry,ection of Endodontics, Veterans General Hospital-Taipei; andhe ‡School of Dentistry, National Yang-Ming University, Tai-an, Republic of China.

Address requests for reprint to Dr. Shue-Fen Yang, Ad-ress: Department of Dentistry, Veterans General Hospital-aipei, 201, Sec. 2, Shih-Pai Road, Taipei, Taiwan, 11217.-mail address: sfyang@vghtpe.gov.tw.099-2399/$0 - see front matter

Copyright © 2006 by the American Association ofndodontists.oi:10.1016/j.joen.2006.04.008

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32 Lu et al.

omplete cleaning and shaping is the key to successful endodontic treatment. Athorough understanding of the internal anatomy and morphology of the root canal

ystem is an important consideration when performing cleaning and shaping proce-ures. Variation in the root canal system of mandibular first premolar has been re-orted (1, 2). In 1973, Zillich and Dowson reported 23.1% of mandibular first pre-olars had two or three root canals radiographically (1). Vertucci using a transparentethod found 25.5% of 400 mandibular premolars had two apical openings and 0.5%

f the teeth had three apical openings (2).Root canal morphology can also vary in different ethnic groups (3– 6). Using a

adiographic technique, Miyoshi et al. reported 13.8% of a Japanese population had twoanals (3). Trope et al. in a radiographic study found black individuals had a higherncidence (32.8% versus 13.7%) of two root canals in mandibular first premolars whenompared to the white population (4). Walker reported 34% southern Chinese had twoanals and 2% had three canals radiographically (5). Sert et al. found that 62% ofandibular first premolars had a single canal in the Turkish population (6). C-shaped

oot canals have also been demonstrated in mandibular first premolars (7–9). Burnseported a fine ribbon-shaped canal system in mandibular first premolars (7). In 1992,aisden et al. using the cross section method reported a 14% incidence of C-shapedanals in 106 mandibular first premolars in a United States population (8). In 1994,ikri also studied mandibular premolars in an Indian population using the cross sectionethod. Results indicated 10% of 112 mandibular first premolars exhibited C-shaped

anals (9).Little information was known regarding the root canal anatomy and morphology of

he mandibular first premolar in the Chinese population. Therefore, the purpose of thistudy was to investigate the root canal morphology of mandibular first premolars in ahinese population using the cross section method.

Materials and MethodsMandibular first premolars extracted because of caries, periodontal diseases,

rauma or for orthodontic reasons were collected from the Department of Oral andaxillofacial Surgery of Taipei-Veteran General Hospital. Eighty-two mandibular left

nd right first premolars with mature and intact root structure and devoid of fracturesere utilized in this study. Each tooth was individually stored in Cidal-Dur (2.3%lutaraldehyde, Veterans Pharmaceutical Plant, Taiwan) for disinfection. The teeth werehen placed in 2.5% NaOCl solution for 1 day to remove organic substances. Photo-raphs of the mesial, distal, buccal, and lingual surfaces for each premolar were madesing a digital camera (Digital Camera E990, Nikon Co., Japan) at a distance of 70 mm.ny groove or depression on root surfaces, apical bifurcation, or other anatomic vari-nces were recorded.

The root length from cementoenamel junction to apex for each tooth was mea-ured. Then, each tooth was embedded in clear resin (Orthoresin, Detrey Densply S.A.,ngland). Starting from root apex, each tooth was resected perpendicular to the longxis at 3, 6, 9, and 12 mm using an electric trimmer (Whip Mix, Co., USA). Each sectionas polished with sand paper under running water, dried and stained with methylenelue. Digital photographs of root surfaces at 3, 6, 9, and 12 mm were made at 24Xagnification under a surgical microscope (OPMI PROdent; Zeiss, Germany) using the

ounted digital camera (Coolpix 990, Nikon, Japan).

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All the cross-sectional images of the mandibular first premolaroots were examined on a computer screen by two endodontists. Themages for each tooth were evaluated from the most apical section to the

ost coronal section. The number of canals and morphologic config-ration of the root canal system for each tooth was determined andlassified. Disagreement in the interpretation of sections was discussedetween two evaluators until a consensus was reached.

The presence of more than one canal in any cross-section of theoot was classified as complicated. Premolars exhibiting two canals withval, round, or dumbbell-shaped canals were classified as type II, III, orV according to Weine (10). Two additional morphologic configura-

ABLE 1. Canal number and configuration

Canal configuration No. of tooth Percentage

Single canal 44 54%Complicated canal 38 46%

2-canal 18 22%Type II 5 6%Type III 5 6%Type IV 8 10%

C-shaped canal 15 18%C1 1 1%C2 1 1%C3 13 16%

Circumferential canal 5 6%Total 82 100%

igure 1. A representative mandibular first premolar with a C-shaped canal, coronally, a deep folding groove on proximal lingual area; (A) 3 mm from ape

igure 2. One of the C-shaped root canal on a mandibular first premolar, clas

oronally, a deep groove on proximal lingual area; (A) 3 mm from apex; (B) 6 mm

OE — Volume 32, Number 10, October 2006

ions of the complicated root canal system were noted and classified asC-shaped canal and circumferential canal.

Teeth with the presence of C-shaped configuration in any oneross-sections of the root were placed in this category. The C-shapedanals were sub-classified in the following categories according to Fan’slassification (11) for the mandibular second molar. Category 1(C1):he shaped was an uninterrupted C with no separation or division.ategory II (C2): the canal shape resembled a semicolon resulting fromdiscontinuation of the C outline. Category III (C3): two or three sep-

rated canals and a discernible isthmus linking them.The unique finding of circumferential canals is reported in this

tudy for the first time. Circumferential canals presented as single canaln the center and 3 or 4 canals at the circumference when viewed inross-section. It was a single canal splitting into several canals (apicalelta) at apical 3 mm from sagital view.

ResultsThe results were summarized in Table 1. Only 54% (44/82) of the

andibular first premolars in this investigation had a single root canal.he other 46% of the mandibular first premolars demonstrated variednd more complicated root canal systems. There were 18 (22%) pre-olars with two canals, 15 (18%) with a C-shaped canal configuration,

nd five (6%) with previously unreported circumferential canals. The8 two-canal premolars included five teeth (6%) with type II morphol-

d as C3, three separate canals with discernible isthmus apically, single canal6 mm from apex; (C) 9 mm from apex.

as C3, multiple separate canals with discernible isthmus apically, single canal

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from apex; (C) 9 mm from apex.

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gy, five teeth (6%) with type III morphology, and eight teeth (10%)ith type IV morphology.

All C-shaped configuration premolars had an associated groove oroncavity on the external root surface (Figs. 1-3). The groove or con-avity frequently presented on the proximal lingual area of the middleoot and did not always extend to the root apex (Fig. 3A). The C-shapedorphology was found in apical 3 mm and/or 6 mm level cross-sectionsith their coronal sections demonstrating a single oval or two canals inn oval-shaped root (Fig. 1-3).

All mandibular first premolars with the circumferential canal con-iguration had a blunt root tip. In each case, the root exhibited a singleanal in the coronal sections with division into multiple canals at theircumference being noted in the apical 3 mm cross-section (Figs. 4nd 5).

DiscussionDifferent methods have been used to study the root canal morphol-

gy of mandibular first premolar (1–5, 7–10). In a radiographic study,alker found 34% southern Chinese had two canals and 2% had three

anals (5). While the radiographic method is noninvasive, it presents awo dimensional image of a three dimensional object and does noteveal the complexity present in the root canal system. The transparentethod can demonstrate the structure and continuity of root canal

ystem from pulp chamber to root apex. The cross section method

igure 3. One of the C-shaped root canal on a mandibular first premolar, classmm from apex; (B) 6 mm from apex; (C) 9 mm from apex.

igure 4. (A–C) Three circumferential canals at 3 mm from apex from three mandib

34 Lu et al.

ombined with the magnification used in this study clearly exposed theomplexity of root canal system and provided impressive images of the-shaped and circumferential canals.

Serial axial computed tomography (CT) has been used to investi-ate the C-shaped canals in mandibular secondary molars (12) and maye a technique for future studies involving mandibular premolars. Aombination of CT followed by the transparent method or cross sec-ional evaluations would be interesting.

In the study conducted by Baisden et al., 15 (14%) mandibularirst premolars revealed a C-shaped canal. Thirteen of those C-shapedanal premolars were also classified as type IV; two were also classifieds type I canal. They noted that C-shaped canals in mandibular premo-ars were associated predominantly with type IV canals (7). In ourtudy, the C-shaped canal was classified independently since C-shapedanals were found not only associated with bifurcation but also trifur-ation or quadrafurcation (Fig. 1A, 2A).

The C-shaped morphology in mandibular second molars is mostlyound coronally and within 3 mm below the cementoenamel junction11). The location of the C-shaped morphology in the mandibular firstremolar is quite different. In this study, the location of C-shaped canalas found at apical 3 mm and/or 6 mm level cross-sections. Coronally,

t could be single oval or two canals. Therefore, C-shaped canals woulde difficult to detect from coronal approach. An additional consider-tion was the finding that the corresponding groove of C-shaped canal

s C2, a semicolon apically, two canals coronally, a groove on mesial wall; (A)

ified a

ular first premolars.

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n the external root surface was varied. Some were deep and foldingrooves, while others were not distinguished or just like shallow con-avities.

For C-shaped root canal in mandibular second molar, Fan et al.nvestigated features of C-shaped mandibular second molars and theross-sectional shapes of their root canal systems in 58 extracted man-ibular second molars from a Chinese population. Teeth were scannedt 0.5-mm increments using micro-CT and observed at 11 levels. Mostrifices 98.1% were found within 3 mm of the cementoenamel junction.ost specimens demonstrated an orifice with an uninterrupted

-shape. The ratio of the deepest part of the external groove to theuccal-lingual thickness was about 48% (11).

Jin et al. investigated the prevalence and configuration of the C-haped canal using CT in 200 teeth. The authors compared the thicknessf the remaining tooth structure from the center of the canal to the outerurface of the deepest groove. C-shaped canals were found in 44.5% ofhe teeth and almost all the grooves were directed lingually (99%). Theontinuous C-shaped canal was the most frequently found (49%). Theuthors found the thinnest remaining tooth structure in the groove areaf the C-shaped mandibular second molar was not different from that ofhe danger zone of normal mandibular second molar at the three levels12). In contrast Chai and Thong studied the cross sectional morphol-gy of 20 mandibular molars with C-shaped configurations. Cross-sec-ional evaluations showed that 27% were a complete C, 64% demon-trated an incomplete C, and 9% were non-C. The mean value for theinimum width of the lingual canal wall was 0.58 � 0.21 mm and the

uccal wall was 0.96 � 0.26 mm, suggesting a risk of perforation on thehinner lingual wall. The buccal and lingual canal walls were frequentlyarrower at mesial locations (13).

Many complicating factors make the C-shaped configuration of theandibular first premolar difficult to treat. It would be clinically rele-

ant to know the mean value for the minimum widths of C-shaped canalall in mandibular first premolars. Anatomically the diameter and widthf mandibular first premolar is much smaller than mandibular secondolars. The small size of mandibular first premolar limits the coronal

ccess to the complex root canal system that, unlike the mandibularecond molar, is found apically.

The identification of circumferential canals is also clinically important.ll the mandibular first premolars in the circumferential canal category

igure 5. A representative mandibular first premolar with a circumferential canpex; (B) 6 mm from apex; (C) proximal view of the whole tooth.

emonstrated multiple canals in the apical 3 mm section. Failure of root

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anal treatment of mandibular first premolars in cases where there appearso be a simple anatomical configuration could be related to tissue andacteria in apical delta. Based on findings in this study, root-end resection ofore than 3 mm might be considered when treating failed cases surgically.

n addition, the operator should carefully examine the resected root-end forircumferential openings using the microscope.

Slowey thought that mandibular premolars were probably the mostifficult teeth to treat endodontically (14). The varied anatomy and mor-hology in mandibular first premolar implies cleaning and shaping will beifficult. In this study, the results revealed only 54% of the mandibular firstremolar in the Chinese population had a single canal. Twenty-two percentontained two canals. The other 24 % had either C-shaped canals or cir-umferential canals. The clinician should view this tooth group as complexnd use all available armamentaria to achieve a successful outcome. Failureo recognize anatomical complexities will result in treatment failure. Inonsurgical treatment, clinicians should employ microscopy, angled pre-perative and working length radiographs, and apex locators to ensure aositive outcome. Surgical intervention may be required when nonsurgical

reatment fails. Microscopy should be employed. Because the most variedonfiguration was located within 3 to 6 mm from root apex in our study, rootnd resection for more than 3-mm may be considered when variations aredentified.

AcknowledgmentsSpecial thanks are given to Dr. John Corcoran and Dr. William

. Johnson for their revision of this manuscript.

References1. Zillich R, Dowson J. Root canal morphology of mandibular first and second premo-

lars. Oral Surg Oral Med Oral Pathol 1973;36:738 – 44.2. Vertucci F. Root canal morphology of mandibular premolars. J Am Dent Assoc

1978;97:47–50.3. Miyoshi S, Fujiwara J, Tsuji Y, Nakata T, Yamamoto K. Bifurcated root canals and

crown diameter. J Dent Res 1977;56:14254. Trope M, Elfenbein L, Tronstad L. Mandibular premolars with more than one root

canal in different race groups. J Endod 1986;12:343–5.5. Walker RT. Root canal anatomy of mandibular first premolars in a southern Chinese

ltiple canal apically, single canal coronally, Note blunt root tip; (A) 3 mm from

al, mu

population. Endod Dent Traumatol 1988;4:226 – 8.

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6. Sert S, Aslanalp V, Tanalp J. Investigation of the root canal configurations of man-dibular permanent teeth in the Turkish population. Int Endod J 2004;37:494 –9.

7. Cohen S, Burns RC. Pathways of the pulp, 8th ed. St. Louis: CV Mosby, 2002:174.8. Baisden MK, Kulid JC, Weller RN. Root canal configuration of the mandibular first

premolar. J Endod 1992;18:505– 8.9. Sikri VK, Sikri P. Mandibular premolars: aberrations in pulp space morphology.

Indian J Dent Res 1994;5:9 –14.

0. Weine F. Endodontic therapy, 6th ed. St. Louis: CV Mosby, 2004:108 –10.

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1. Fan B, Cheung G, Fan MW, Gutmann JL. C-shaped canal system in mandibular secondmolars: part I-anatomical features. J Endod 2004;30:899 –903.

2. Jin GC, Lee SJ, Roh BD. Anatomical study of C-shaped canals in mandibular secondmolars by analysis of computed tomography. J Endod 2006;32:10 –3.

3. Chai WL, Thong YL. Cross-sectional morphology and minimum canal wall widths inC-shaped roots of mandibular molars. J Endod 2004;30:509 –12.

4. Slowey RR. Rot canal anatomy. Road map to successful endodontics. Dent Clin North

Am 1979;23:555–73.

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