Year : 2010 | Volume
: 21 | Issue : 2 | Page : 169--173
Assessment of root canal morphology of mandibular first premolars in the Indian population using spiral computed tomography: An in vitro study
Raghu Sandhya, Natanasabapathy Velmurugan, Deivanayagam Kandaswamy
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai - 602 102, India
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai - 602 102
Aim: The aim of the study is to determine the root canal morphology of the mandibular first premolar teeth in an Indian population using spiral computed tomography (SCT).
Materials and Methods: One hundred extracted mandibular first premolars were observed using Spiral Computed Tomography for the (i) Pattern of root canal (ii) Tooth length (iii) Position of the bifurcation of the canal (iv) Invagination of the root (v) Root thickness. The root canal morphology was classified based on Vertucci«SQ»s classification.
Results: Eighty percent of the teeth had a single canal, 11% of the teeth had two canals, and C-shaped canals were found in 2% of the teeth, in this study. The average length of the teeth was 21.6 mm. Fourteen percent of the teeth had mesial invagination of the root.
Conclusion: The Type I root canal morphology was the most common type of root canal system in the mandibular first premolars among the Indian population in this study.
|How to cite this article:|
Sandhya R, Velmurugan N, Kandaswamy D. Assessment of root canal morphology of mandibular first premolars in the Indian population using spiral computed tomography: An in vitro study.Indian J Dent Res 2010;21:169-173
|How to cite this URL:|
Sandhya R, Velmurugan N, Kandaswamy D. Assessment of root canal morphology of mandibular first premolars in the Indian population using spiral computed tomography: An in vitro study. Indian J Dent Res [serial online] 2010 [cited 2021 Apr 16 ];21:169-173
Available from: https://www.ijdr.in/text.asp?2010/21/2/169/66626
Knowledge of the root canal morphology and its variations is essential to achieve success consistently in an endodontic treatment. Variation in the root canal anatomy is a commonly occurring phenomenon. These variations may be attributed to the differences in gender  and racial origin.  The mandibular first premolars are known for the complex nature of their canal configuration.  Earlier studies have reported a high occurrence of Type I canal pattern.  These teeth are difficult to treat endodontically and show a high failure rate, possibly due to the extreme variations in the root canal morphology.  Root canal morphology of the mandibular first premolars has been reported based on the study of various population groups, including the Chinese,  Turkish,  American, , Mexican,  and African American population.  Literature reviews have found that studies on the root canal morphology of teeth from an Indian population were scarce. Studies on root canal anatomy are usually done by radiography,  clearing technique,  direct observation with a microscope,  3D reconstruction,  and macroscopic sections. , Conventional radiography has the problem of superimposition,  and moreover it is a two-dimensional representation of a three-dimensional object. The difficulties encountered with other methods of study include disturbance of the pulp space and its surrounding structures during preparation of the teeth.
The advancements in the field of radiology have drawn upon the use of computed tomography (CT) for imaging teeth. Eder et al. reported that CT is a viable tool for the evaluation of unclear root canal configurations. Spiral computed tomography (SCT) is useful in assessing the unusual root canal morphology when compared to the routine intraoral periapical radiographs. , Cimilli et al. demonstrated C-shaped canals in the mandibular second molars by using SCT and reported that high resolution visualization of the root canal shape can be achieved by SCT imaging. The aim of this in vitro study was to determine the root canal morphology of the mandibular first premolars in an Indian population, using SCT.
Materials and Methods
One hundred extracted mandibular first premolars in an Indian population were collected from the dental hospitals in India. Teeth with deep caries, metallic restorations, fractures, teeth with incompletely formed roots, and those which were endodontically treated were not included. All attached soft tissue and calculus were removed using an ultra sonic scaler (EMS, Electromedical systems, Dallas) and the teeth were mounted on a polyethylene sheet in rows and columns of ten. The teeth were so arranged as to maintain the apices of the roots of each row in a single plane. A 64-slice spiral CT scan (Fifth generation SIEMENS SOMATO DUO, GERMANY) was used to scan the 100 premolars simultaneously. A section thickness of 0.6 mm and a section position of 0.3 mm were obtained at 120 kVp and 83 mA. A Gantry angulation of 0 was used, and the reconstruction matrix contained 512 x 512 pixels. The software used to view the scanned teeth was the SIENET Sky - DICOM CD Viewer. The scan reports included cross-sections, buccolingual longitudinal sections, and mesiodistal longitudinal sections. The canal patterns were observed in the cross-sectional and longitudinal section views of the SCT. Apart from the canal morphology, the tooth length, position of bifurcation of canal, number of premolars with invagination of the root, and the root thickness were also determined.
Vertucci's classification  was used to determine the pattern of the root canal.
Type I: A single canal extends from the pulp chamber to the apex (1).
Type II: Two separate canals leave the pulp chamber and join, short of the apex, to form one canal (2-1).
Type III: One canal leaves the pulp chamber and divides into the root; the two then merge to exit as one canal (1-2-1).
Type IV: Two separate, distinct canals extend from the pulp chamber to the apex (2).
Type V: One canal leaves the pulp chamber and divides short of the apex into two separate, distinct canals, with separate apical foramina (1-2).
Type VI: Two separate canals leave the pulp chamber, merge in the body of the root, and redivide short of the apex to exit as two distinct canals (2-1-2).
Type VII: One canal leaves the pulp chamber, divides and then rejoins in the body of the root, and finally redivides into two distinct canals short of the apex (1-2-1-2).
Type VIII: Three separate, distinct canals extend from the pulp chamber to the apex (3).
Pattern and percentage of each canal type
The Type I canal [Figure 1] A1 to A5 was found to be the most prevalent canal pattern (80%) [Table 1]. The Type II [Figure 1] B1 to B5 canal pattern was observed in 9% of the teeth. Type III [Figure 1] C1 to C5, IV [Figure 1] D1 to D5, and V [Figure 1] E1 to E5 canal patterns occurred in 3, 2, and 4% of the teeth, respectively. No teeth with Types VI, VII, and VIII canal patterns were identified in this study. Two percent of the teeth had C-shaped canals. The cross-sectional views of the teeth with C-shaped canals were studied at various levels. The canals in these teeth resembled the letter 'C' at the coronal third, which divided into three at the middle third and exited as one canal at the apex [Figure 2]. They were classified as Category III sub division I according to Melton's classification of C-shaped canals. 
The longest tooth in this study was 25.2 mm and the shortest tooth was 17.7 mm in length. There were 35 teeth, which had lengths ranging between 19 and 21 mm and another 35 teeth whose lengths ranged between 21 and 23 mm.
Average: 21.6 mm
Median: 21.3 mm
Mode: 21.3 mm
Standard Deviation: 1.65
Bifurcation of the root canal
The number of teeth with canal bifurcation (samples that had a single canal that divided into two) was found to be seven. The level at which the canal bifurcation occurred was measured from the crown tip. The average length from crown tip to point of canal bifurcation was found to be 13 mm.
Mesial invagination of the teeth
Fourteen percent of the teeth had a mesial invagination of the root. Of these 14 teeth, seven teeth were found to have a Type I canal. One tooth had a Type II canal, two teeth had a Type IV canal, and four teeth had a Type V canal pattern. The point at which the mesial invagination of the root initiated was measured from the crown tip.
Length from the crown tip to the point of initiation of mesial invagination:
Average: 14.15 mm
Median: 14.15 mm
Standard deviation: 1.53
Root thickness at the point of maximum mesial invagination
Measurements of root thickness at various levels of teeth revealed that the root thickness was reduced in relation to the mesial invagination. Positions of the maximum points of invagination for the 14 teeth were observed. They were located at the cervical one-third of the root in one tooth, at the middle one-third in 12 teeth [Figure 3], and at the apical one-third in one tooth. The root thickness at this point was measured [Table 2]. The average root thickness at the cervical one-third was 0.8 mm, at the middle one-third was 0.78 mm, and at the apical third was 0.3 mm. Root thickness of teeth without mesial invagination was also measured. Its average at the cervical one-third was 1.85 mm, at the middle one-third was 1.33 mm, and at the apical one-third was 1.09 mm. [Figure 3] shows the cross-sectional view at the middle one-third of a root, which has a remaining root thickness of only 0.5 mm, in relation to the mesial invagination.
In the current study SCT was used to analyze the canal morphology of the mandibular first premolars among an Indian population. SCT acquires a raw projection data with a spiral-sampling locus in a relatively short period, by employing a translation of the subject through the X-ray source, with continuous rotation of the source-detector assembly.  Without any additional scanning time, these data can be viewed as conventional transaxial images, as multiplanar reconstructions, or as three-dimensional reconstructions  Gopikrishna et al. had reported a rare case of a maxillary first molar having a single root with a single canal, which was confirmed with the aid of an SCT. Of late, Suma et al. reported the usefulness of SCT in the diagnosis and endodontic management of an unusual case of a mandibular second molar fused with a paramolar. Reuben et al. used SCT for an in vitro study of the root canal morphology of mandibular first molars among the Indian population. They concluded that SCT was a useful tool for assessing root canal morphology. Hence SCT was used in this study for an in vitro evaluation of the root canal anatomy of the mandibular first premolar.
Nowadays, the limited cone beam CT device for dental use (Ortho-CT) with improved operability and resolution, and reduced radiation doses is available.  Currently, micro-computed tomography (MCT) is also available as a noninvasive technique for imaging teeth. Nielsen et al. have reported that the MCT is a new and innovative tool for endodontic research. Fan et al. have successfully used MCT for studying the root canal systems in mandibular first premolars with C-shaped root configurations. These recent advanced devices can also be used for analyzing root canal morphology.
The most prevalent canal pattern in this study was Type I, occurring in 80% of the mandibular first premolars [Table 1]. Other studies have shown that the Type I canal pattern occurred in about 67.2 to 86.3% , of the mandibular first premolars.
The Type II canal pattern was encountered in 9% of the samples in this study, whereas, Vertucci's  study did not report any Type II canals. The Type V canal pattern was identified in 4% of the samples. However, the same in Vertucci's study was observed in 24% of the teeth. Vertucci  also reported that 74% of the mandibular first premolars had a single canal and 25.5% of the teeth had two canals. In case of African American patients the incidence of two or more canals was 32.8%, whereas, the incidence in a Caucasian group was about 13.7%.  These variations may be attributed to the differences in gender  and racial origin. 
A challenging anatomic variation of a root canal is the presence of a C-shaped canal. This anatomy is much more common in Asians than Caucasians.  Vertucci  reported the occurrence of a C-shaped canal in 0.5% of the mandibular first premolars. Lu et al. reported the incidence of C-shaped canals in the Chinese population to be 18% and Baisden et al. indicated the existence of a C-shaped canal in 14% of the mandibular first premolars. Sikri and Sikri  investigated the aberration of pulp space morphology using radiography and the cross-section method. He reported that the prevalence of a C-shaped canal in an Indian population was 10.7%, whereas, in our study among the Indian population, it was identified only in 2% [Table 1] of the samples. Approximately 10% of the mandibular first premolars exhibited a C-shaped canal. The C-shaped canals encountered in this study are of Category III subdivision I according to Melton's classification of C canals. 
The average length of the mandibular first premolar was reported to be 22.5 mm  and 21.6 mm  in previous studies. The average length among this Indian population was found to be 21.6 mm. A single canal, which leaves from the pulp chamber, may divide at any level before its exit at the apex. In this study 7% of the mandibular first premolar teeth had a single canal dividing into two. The average length from the crown tip to the point of canal bifurcation was 13 mm. In an earlier study the point of canal bifurcation was found to be 7.4 mm from the cementoenamel junction, in case of the mandibular premolars. 
In the previous studies on canal anatomy using radiographs, mesial invagination of the root was not reported. It is a deep developmental groove located on the mesial surface of the root. The only in vivo study that had reported them was a study done by Robinson et al. using the SCT. He had reported that 15% of the mandibular premolars had mesial invagination. In this study 14% of the teeth had mesial invagination. In all these samples, the root thickness around the canal was reduced in the invaginated area [Table 2]. The point of maximum invagination was most commonly located in the middle one-third of the root [Table 2]. At the point of maximum invagination, the root thickness in the tooth with mesial invagination was comparatively lesser than in the tooth without mesial invagination. This indicates a need for careful cleaning and shaping during an endodontic procedure. Any overzealous enlargement of the root canal can lead to perforation. However, further analysis is required to substantiate this finding.
Among the Indian population, the Type I root canal morphology occurred more frequently (80%) in the mandibular first premolar teeth. SCT is a useful tool in assessing the morphology of root canal, the point of canal bifurcation, the tooth length, and the root thickness, as also in identifying mesial invagination of the root.
Meenakshi Ammal Dental College and Hospital, Chennai, India.
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