Int J Oral-Med Sci 13(3):81-88, 2015 81

Original Article

Morphological Variations of the Root Canal System in C-shaped Roots of the Mandibular Second Molar in a Japanese Population

Makoto Suzuki,1 Yasuhisa Tsujimoto,2 and Shintaro Kondo3

1Nihon University Graduate Schoolof Dentistry at Matsudo, Endodontics, Matsudo, Chiba 271-8587, Departments of 2Endodontics, 3Anatomy, Nihon University Schoolof Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan

Article History Abstract

Received November 2014 Morphologicalvariationsof the root canalsystem of C-shaped roots in mandibularsecond Accepted December 2014 molars of young Japanese patients (aged 20 to 29 years old) were analyzed by using multi- detector row computed tomography (MDCT) in order to clarify the entire picture from the orifice to the apex. CT images were reconstructed so that the axialimage was inclined perpendicular to the long axis of teeth. C-shaped roots were more frequently found in females (54.0%) than in males (36.7%) (p<0.01). One root canal was most frequently Keywords : found on the coronalside, and the root canalnumbers increased to the apex. Thus, in many C-shaped root canal, cases at the coronallevelthecanalformed letter?C@ , but it ramified into increasingly multi-detector row computed tomog- smaller canals towards the apex. The complex configuration of the root canals may be raphy, root canaltreatment, related to various degree of fusion in the roots. The results of this study might be used for , sinodonty understanding the nature of C-shaped root canals.

Introduction phy (CT) was used for the observation of root canal Mandibular second molars with incompletely fused roots systems(15-25). CT can be applied in patients whose often exhibit a C-shaped root. The mesialand distalroots gender and age are identified, and without extraction. appear fused on the buccalside, but are separated by a CT images can be observed not only as two-dimensional longitudinal gutter on the lingual side. When two roots are images including oblique slices, but also reconstructed for fused and C-shaped, the root canals may also exhibit the three-dimensional modeling. The pulp cavity becomes same morphology(1). It is difficult to achieve complete narrow with aging because of secondary and tertiary dentin debridement of the C-shaped root canalsystem due to its formation(26). So the pulp cavities of elders vary morpho- morphological complexity(2); fin and isthmus often appear logically. The pulp cavity of young people showed funda- between the incompletely and / or completely fused root mentalstructures without age-relatedchanges. canals(3). The difficulties in C-shaped root canal treatment The root canal system in mandibular second molars with are thought to be caused by the morphological complication C-shaped roots in Chinese populations was studied morpho- of the root canalsystems. Detailedanatomicaldescriptions logically (19, 23). These two studies analyzed similar of the C-shaped roots and root canals may help in subjects, but reported different results; Min et al.(23) understanding their complicated structure. showed that two root canals at the orifice were common, but Previous studies of C-shaped root canalsystems in Zheng et al.(19) reported fused root canals at the orifice. extracted teeth used teeth samples that were injected with There have been few studies that analyzed serial cross- Indian ink and made transparent by methylsalicy- sectionalstructures from orifice to apex. The present study late(4-12), polyester resin cast replicas(3), and serial cross- analyzed root canal systems with C-shaped roots of sections of roots (1,3,13,14). Recently, computed tomogra- mandibular second molars in young Japanese patients (aged 20 to 29 years old) by Multi-detector row CT (MDCT) Correspondence to : Makoto Suzuki imaging. Specialattention was given to the entire structure E-mail: [email protected] of the canalsystems from orifice to apex. 82 Int J Oral-Med Sci 13(3):81-88, 2015

Materials and Methods We used the MDCT images of 579 patients (281 males, 298 females; age 20-29 years) who underwent 64-row MDCT for diagnostic purposes of oraldiseases in the Department of Radiology at the hospital attached to the Nihon University Schoolof Dentistry at Matsudo, Chiba, Japan, from January 2009 to December 2011. 64-row MDCT was conducted using Aquilion™ 64 (Toshiba Medical Systems Corporation) with 64-detector-row CT in the craniocaudaldirection. Allpatientswere scanned by MDCT Fig.1 Location of measurements in C-shaped root canalof the according to the routine clinical protocol for craniomaxillofa- mandibular second molar cial examination as follows: tube voltage 120 kV, tube CEJ; Cemento-enameljunction, LevelA; floorof pulp chamber 3 mm belowthe CEJ, LevelB; coronalthird part, current 100 mA, field of view 240×240 mm, helical pitch 41, LevelC; middlepart, LevelD; apicalthird part. and 1.0 sec/rotation. The MDCT images of the mandibular second molar region were used in this study, and the slices Type 2: root canals resembling a semicolon (MB-D were 0.3 mm thick and parallel to the occlusal plane. Teeth canaland ML canal) with extensive caries, root canal filling, restorations and Type 3: root canals resembling a semicolon (DB-M metalartifact were excluded.This study was approved by canaland DL canal) the Ethics Committee of Nihon University Schoolof Type 4: two ovalroot canals(M canaland D canal) Dentistry at Matsudo (No. EC11-037). Type 5: two round root canals (M canal and D canal) In this study, if three-quarters or more length of the Type 6: three root canals buccalroot trunk was one root, it was considered as a C- Type 7: a round root canal shaped root; a completely fused root was not included as a C- Type 8: four root canals shaped root. For analysis of the C-shaped root canal, C- The number of root canals at the four levels (A-B-C-D) in shaped roots on the right side of the were used. each patient was determined. The sex differences were MDCT images were reconstructed using 3-D imaging analyzed by chi-square test at a significance level of p<0.05 software (RealiaPro, Cybernet Systems Co., Ltd., Tokyo) on or 0.01 using SPSS 17.0 statisticalsoftware. the personalcomputer, and the axialimage was inclined perpendicular to long axis of the mandibular second molar. Results The present study observed cross-sections at various levels The frequency of C-shaped roots in the mandibular of the root canals. Plane A was within 3 mm below the second molar is shown in Table 1. Among the 281 male cemento-enameljunction (CEJ), because Min et al.(23) patients, 103 (36.7%) had C-shaped roots on either the right reported that the pulp chamber floors of C-shaped root were or left side, or both sides, and 63 (22.4%) of 103 had bilateral 90.91% within 3 mm below the CEJ. The shape of the pulp C-shaped roots, and one had a completely fused root on the cavity of C-shaped root was observed at the following four right side and two root on the left side. Among the 298 levels of the plane; plane A was the pulp chamber floor 3 mm female patients, 161 (54.0%) had C-shaped roots on either below the CEJ, plane B was the coronal third part (one- the right side or left side or both, and 127 (42.6%) of 161 had third the distance between the CEJ and the anatomicalapex bilateral C-shaped roots. C-shaped roots were more fre- below the CEJ), plane C was the middle part (middle part quently found in females than males (p<0.01). from CEJ to apex), plane D was the apical third part (one- Morphological characteristics of the C-shaped root canal third the distance between the CEJ and the anatomicalapex at the four levels are shown in Table 2. There was no above the apex)(Fig. 1). difference between males and females in the frequencies. At The canal shape at each selected level was classified into level A, type 1 was the most frequently found (63.0% in the following criteria modified from that reported by Min et males, 70.6% in females), followed by type 4 (16.0% in al.(23)(Fig. 2). males, 14.0% in females). At level B, type 1 was the most Type 1: a continuous C-shaped root canal frequently found (37.0% in males, 41.2% in females), Int J Oral-Med Sci 13(3):81-88, 2015 83

Fig.2 Classification of the root canal shape on cross-sections

Table 1 Root morphology of mandibular second molar

Table 2 Type of the C-shaped root canal morphology at different levels

followed by type 2 (28.4% in males, 27.2% in females). At of root canals differed with gender. In males, type 2 was level C, type 2 was the most frequently found (33.3% in most frequently found (25.9%), followed by type 6 (22.2%), males, 36.0% in females), followed by type 6 (23.5%) and type 5 (21.0%), and type 1 (17.3%). In females, type 5 was type 1 (21.0%) in males, type 1 (25.0%) and type 6 most frequently found (33.1%), followed by type 1 (20.6%), (16.2%) in females. At level D, the morphological variations type 7 (16.9%), and type 2 (14.7%). 84 Int J Oral-Med Sci 13(3):81-88, 2015

Table 3 The number of C-shaped root canals each patients of C-shaped root

The numbers of root canals at the four levels are shown in (18.4%) and A1B2C2 (18.4%) in females. Fig. 4 shows Table 3. We listed the number of root canals in order from some examples of MDCT images of root canal number with levelAto levelD.One root canalwas seen at levelAin more C-shaped root. than 60%. At level B three root canals in around 10%, half of the remaining 90% showed one root canal, and the other half Discussion showed two root canals. Hence, we used abbreviations for The frequencies of C-shaped roots of the mandibular the expression of root canalnumbers at severalcross- second molar in different ethnic groups (1, 4-9, 12, 13, 16, sectional planes. For example, A1B2C2 represented one root 20, 27, 29) were mapped into three large groups including canal at level A , two root canals at level B and two root Africans, Caucasians and (Table 4). C-shaped canals at level C (Fig. 3). There was no significant root was the most frequently found in the East Asian difference between males and females in the number of root populations (around 30%), followed by Caucasoid popula- canals. A1B1 was most frequently found (38.3% in males, tions (<20%), and the least in the African population (< 41.9% in females), followed by A2B2 (27.2% in males, 10%). The East and south east Asians are included in a 23.5% in females), A1B2 (22.2% in males, 23.5% in Mongoloid population from an anthropological perspective. females). A2B2C2 was most frequently found (23.5%), The Mongoloid population divided into two different groups, followed by A1B1C1 (19.8%), A1B2C2 (17.3%) and i. e, sinodonty and sundadonty, based on the eight dental A1B1C2 (14.8%) in males. A1B1C1 was most frequently traits(28). Sinodonty is widely distributed in Mainland found (22.1%), followed by A2B2C2 (20.6%), A1B1C2 and Japanese islands and North America. On the Int J Oral-Med Sci 13(3):81-88, 2015 85

Fig.3 Schematic representation of three typicalroot canalsystem patterns of C-shaped root A1B1C1, one root canalexisted at levelA,one root canalexisted at levelB,one root canalexisted at levelC. A2B2C2, two root canals existed at level A, two root canals existed at level B, two root canals existed at level C. A1B2C2, one root canal existed at level A, two root canals existed at level B, two root canals existed at level C.

Fig.4 Various patterns of C-shaped root canal at four levels observed in MDCT images. Case 1 : A1B1C1D1 (one root canalexisted at levelA,one root canalexisted at levelB,one root canalexisted at levelC,one root canal existed at level D). Case 2 : A1B1C1D1 (one root canalexisted at levelA,one root canalexisted at levelB,one root canalexisted at levelC,one root canal existed at level D). Case 2 shows a different expression of root and canalshapes from case 1; Case 1 shows C-shape at levelD,but case 2 shows oval. Case 3 : A1B2C2D2 (one root canal existed at level A, two root canals existed at level B, two root canals existed at level C, two root canals existed at level D). Case 4 : A2B2C2D2 (two root canals existed at level A, two root canals existed at level B, two root canals existed at level C, two root canals existed at level D). Case 3 shows different expression of root and canalshapes from case 4; Case 3 shows C-shape at C and D, but case 4 shows independent two ovals

other hand, sundadonty is distributed from accord with the previous studies in Japanese population (1, to Oceanian regions. C-shaped root was more frequently 13, 29), but that in females was higher than in other studies. found in sinodonty (>30%) than in sundadonty (20-30%). Since previous studies had been published several decades In this study, C-shaped roots were found in 36.7% of ago, the discrepancy between the present study and the males and 54.0% of females. The frequency of males was in others may be explained by the effect of microevolution in 86 Int J Oral-Med Sci 13(3):81-88, 2015

Table 4 Frequency of C-shaped roots among different race

the Japanese population. In general, the frequency of the Since C-shaped roots appear in certain strains of mice, a trait depends on the sampling method. The result of present genetic factor seems to play a role in this trait(33). The gene study for the patients as a dentalhospitalcouldnot be causing C-shaped root formation in mice maps close to the necessarily to represent a standard frequency of C-shaped microsatellite loci at D5Mit29, 321 and 427 on chromosome root for a Japanese population. 5(34). In the mouse, roots are fused on the lingual side unlike In this study, C-shaped root was more frequently found in humans(33). The subpulpal lobes are not present in the females than in males (p<0.01). Kotoku(29) reported that developmental stage of pulpal floor formation in mouse(35). females exhibited C-shaped root more frequently than males Therefore, the developmental background differs between did, but some studies showed no significant difference humans and the mouse. between sexes (15, 19). We discuss the sex difference in the We described the root canalnumbers in the C-shaped root C-shaped root based on the development of the pulpal floor. in four cross-sectionalplanes.One root canalwas most The formation of dentine on the pulpal floor is induced by frequently found on the coronal side (level A), and the root the dentalepithelialdiaphragm,but the dentine of the pulpal canalnumbers increased towards the apex (levelB-D).This floor does not always continue to the cervical region of the result is in agreement with some previous studies (19, 25), coronaldentine in the developmentstage. The interradicu- but Min et al.(23) reported that two root canals were most lar dentine develops from a separate mineralization center, frequently found regardless of the levels of plane. The termed the subpulpal lobe, and only later does it unite with subjects of these studies including the present study were of the coronaldentine. The number of subpulpallobes sinodonty, and they were considered to have similar dental determines the root number(30). Takahashi et al.(31) characteristics. Sample sizes in this study and the study of described the presence of two subpulpal lobes on both Zheng et al.(19) were larger (>200) than in the studies of lingual and buccal sides of the two-rooted mandibular molar, Min et al.(23) (around 40). Since a study based on large but the buccalone did not emerge in a C-shaped root. The sample size has high reliability, it was concluded that the difference in number of subpulpal lobes between two-rooted canalnumber wouldincrease from coronalpart to root apex and C-shaped is thought to be related to the size of the in the C-shaped root. buccal part of the crown. Generally, females have smaller The number of root canals was listed in order from level mandibular molar crown than males(32). The buccal A to D (Table 3). The number of root canals, from level A to portion of the developed crown in females is smaller than in B, basically remained the same; the most frequently found males, and it is speculated that the higher occurrence of the was one canal. The same number of root canals from level A C-shaped root in females is related to the smaller crown in to C (A1B1C1 and A2B2C2) were frequently found, the developmental stage(31). followed by one root canal decreased from the orifice down Int J Oral-Med Sci 13(3):81-88, 2015 87

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