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Table of Contents   
ORIGINAL ARTICLE  
Year : 2014  |  Volume : 17  |  Issue : 3  |  Page : 238-243
Analysis of C-shaped canal systems in mandibular second molars using surgical operating microscope and cone beam computed tomography: A clinical approach


1 Department of Conservative Dentistry & Endodontics, Army Dental Center (R&R), Delhi Cantonment, New Delhi, India
2 Maulana Azad Institute of Dental Sciences, Bahadur Shah Zafar Marg, New Delhi, India

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Date of Submission26-Sep-2013
Date of Decision27-Jan-2014
Date of Acceptance04-Feb-2014
Date of Web Publication2-May-2014
 

   Abstract 

Aims: The study was aimed to acquire better understanding of C-shaped canal systems in mandibular second molar teeth through a clinical approach using sophisticated techniques such as surgical operating microscope and cone beam computed tomography (CBCT).
Materials and Methods: A total of 42 extracted mandibular second molar teeth with fused roots and longitudinal grooves were collected randomly from native Indian population. Pulp chamber floors of all specimens were examined under surgical operating microscope and classified into four types (Min's method). Subsequently, samples were subjected to CBCT scan after insertion of K-files size #10 or 15 into each canal orifice and evaluated using the cross-sectional and 3-dimensional images in consultation with dental radiologist so as to obtain more accurate results. Minimum distance between the external root surface on the groove and initial file placed in the canal was also measured at different levels and statistically analyzed.
Results: Out of 42 teeth, maximum number of samples (15) belonged to Type-II category. A total of 100 files were inserted in 86 orifices of various types of specimens. Evaluation of the CBCT scan images of the teeth revealed that a total of 21 canals were missing completely or partially at different levels. The mean values for the minimum thickness were highest at coronal followed by middle and apical third levels in all the categories. Lowest values were obtained for teeth with Type-III category at all three levels.
Conclusions: The present study revealed anatomical variations of C-shaped canal system in mandibular second molars. The prognosis of such complex canal anatomies can be improved by simultaneous employment of modern techniques such as surgical operating microscope and CBCT.

Keywords: Cone beam computed tomography; C-shaped canal systems; Indian population; mandibular second molar; surgical operating microscope

How to cite this article:
Chhabra S, Yadav S, Talwar S. Analysis of C-shaped canal systems in mandibular second molars using surgical operating microscope and cone beam computed tomography: A clinical approach. J Conserv Dent 2014;17:238-43

How to cite this URL:
Chhabra S, Yadav S, Talwar S. Analysis of C-shaped canal systems in mandibular second molars using surgical operating microscope and cone beam computed tomography: A clinical approach. J Conserv Dent [serial online] 2014 [cited 2019 Aug 22];17:238-43. Available from: http://www.jcd.org.in/text.asp?2014/17/3/238/131785

   Introduction Top


The study of root canal anatomy of teeth in different racial groups is of paramount importance because of endodontic as well as anthropological significance. Such knowledge can aid in localization, negotiation and subsequent management of root canal systems. [1]

A lot of studies on root canal systems have been carried out on the teeth from Caucasian populations. The Indian population is considered to be a hybrid of several ethnic groups with characteristics of Caucasian, Mongoloid and Negroid races, which is generally referred to as the Dravidian group. [2] Similar studies among the Indian population are scarce. [3]

A high incidence of C-shaped canal systems among Asian population has been reported. [4] Though this anatomical variant occurs mostly in mandibular second molars, it can also be seen in mandibular first premolar, [5],[6] the mandibular first molar, [7] the maxillary first molar [8],[9] and the maxillary second molar. [10],[11] The main anatomical feature of C-shaped canal systems is the presence of a fin or web connecting the individual root canals. They may appear as a single ribbon shaped opening with a 180° arc linking the two main canals. In general, this canal configuration is found in teeth with fused roots. The floor of the pulp chamber is usually situated deep and may assume an unusual anatomical appearance. The prognosis of such cases can be improved by acquiring better understanding of their anatomy with the use of sophisticated techniques such as surgical operating microscope and cone beam computed tomography (CBCT).

In view of the above, the present study aimed to evaluate C-shaped canal systems according to Min's method through a clinical approach using surgical operating microscope in permanent mandibular second molar teeth. In addition, it was aimed to detect the number of canals and missed canals below the orifices after insertion of K-files and to analyze the minimum thickness between the initial file and external root surface toward the groove at coronal, middle and apical third levels using CBCT technique.


   Materials and methods Top


Forty two freshly extracted mandibular second molar teeth having fused roots and longitudinal grooves were collected randomly from native Indian population by taking prior detailed history. Specimens with any calcification, cracks, structural defects, extensive caries, restoration, endodontic treatment were excluded. Teeth were stored in 10% neutral buffered formalin solution. Any attached soft-tissue and calculus was removed with the help of ultrasonic scaler (ARTP-6, Bonart Med Technologies, USA) before the study.

The access to pulp chamber was made with diamond burs using high speed contra angle airotor hand piece (NSK, Japan) and water spray. Pulp tissue was extirpated and chamber soaked in 5% sodium hypochlorite solution (Cmident India, Delhi) for 2 h. Pulp floor was examined under surgical operating microscope (Carl Zeiss Surgical, Oberkochen, Germany) at ×16 magnification and classified according to Min's Method as under [Figure 1]:

  • Type I: Peninsula-like floor presenting a continuous C-shaped orifice [Figure 1]a.
  • Type II: A buccal, strip-like dentin connection between the peninsula-like floor and the buccal wall of the pulp chamber separating the C-shaped groove into mesial and distal orifices [Figure 1]b.
  • Type III: A mesial, strip-like dentin connection between the peninsula-like floor and the mesial wall, separating the C-shaped groove into a small mesial-lingual orifice and a large arc-like mesiobuccal distal orifice [Figure 1]c.
  • Type IV: Non-C-shaped floors comprising of one distal canal orifice and one oval or two round mesial canal orifices [Figure 1]d.
Figure 1: Classifi cation of C-shaped canal systems (Min's method). Various types of pulp fl oors: Type-I (a), Type-II (b), Type-III (c), Type-IV (d)

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Subsequently, K-file (Dentsply Maillefer) with ISO size #10 or 15 was carefully inserted into each canal orifice until the tip of the file could be seen at the apical foramen. The number of files inserted into the canal system was guided by the shape of orifice with a procedure akin to the clinical situation described by Fan et al. [12] In case the two files were very close and binding each other from orifice to the apex, only one file was selected. The files so inserted were fixed in root canals with wax on the occlusal surface.

All teeth were then subjected to CBCT scan (Carestream Inc., Rochester, NY) (80 kVp, 8 mA, 0.09 mm 3 voxel size) and studied from orifice to the apex at an interval of 0.09 mm in consultation with dental radiologist so as to obtain more accurate results [Figure 2]. The number of the initial files in different canals and number of missed canals were analyzed using cross-sectional and 3-dimensional (3D) images of each specimen (Xelis Dental 3D-Infinitt Inc., Seoul, Korea).
Figure 2: Negotiation of C-shaped canal systems. Type-I: a-c, Type-II: d-f, Type-III: g-i and Type-IV: j-l. (a-Coronal, b-Middle and c-Apical level)

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The missed canals were classified as below:

  1. Missed main canal-canal missed entirely from orifice to the apex [Figure 3] and
  2. Partially missed canal-canals missed at any level between orifices to the apex [Figure 4].
Figure 3: Missed canals (complete): 3D sagittal views (a-d), 2D and 3D cross-section views-coronal (e and f), middle (g and h) and apical level (3i and j)

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Figure 4: Missed canals (partial): 3D sagittal views (a-d), 2D and 3D sagittal and cross section views-coronal (e-g), middle (h-j) and apical level (k-m)

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The minimum distance between the external root surface on the groove and the file placed in the canal was measured at coronal, middle and apical third respectively using CS 3D imaging software.

The statistical analysis was performed using one-way analysis of variance (ANOVA) and t-test to determine whether significant differences in the minimum distance existed among various types of pulp floors. All statistical operations were carried out through Statistical Presentation System Software (SPSS Version 8) for Windows (SPSS Inc, Chicago, IL).


   Results Top


Classification of C-shaped canal system

(Min's method)


Out of total 42 samples of teeth observed under surgical operating microscope, there were 33 teeth (78.57%) with C-shaped floor and remaining 9 samples (21.43%) presented with non-C-shaped configuration (Type-IV). Among 33 C-shaped teeth, 7 (16.66%) samples depicted Type-I, 15 (35.72%) Type-II and remaining 11 (26.19%) Type-III configuration [Table 1].
Table 1: Classification of C-shaped canal system at pulp floor level (Min's method)

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Initial files in different orifices

A total of 100 files were inserted in 86 orifices of various types in all 42 specimens. Pulp chamber floors displaying Type-I configuration (continuous C-shaped) had 11 files with 1 file (4 orifice), 2 files (2 orifices) and 3 files (1 orifice). Types-II, III and IV specimens had a total number of 39, 31 and 19 initial files respectively.

Missed canals at various levels

CBCT scan images revealed that a total of 21 canals were missing completely or partially from orifice to the apex. 4 (19.05%) canals were found to be missed completely (2 in Type-I, 1 each in Type-II and Type-IV). Seventeen canals (80.95%) were observed as partially missed canals at various levels. Two specimens (4.76%) were observed with partially missed canals at coronal and middle third level (1canal each in Type-IV) and 15 (35.71%) at apical third level (2 in Type-I, 11 in Type-II, 1 each in Types-III and IV) [Table 2].
Table 2: Missed canals at various levels

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Minimum thickness between initial file

and external surface on the groove


The mean values for the minimum thickness between the initial file and the external surface of root on the groove were highest at coronal third followed by middle and apical third levels in all the categories. Lowest values were obtained for teeth with Type-III category at all three namely coronal, middle and apical third levels. On the other hand, the highest mean of values were calculated in Type-I category at coronal third level and Type-IV category in middle and apical regions [Table 3].
Table 3: Minimum thickness between initial file and external surface of the groove

Click here to view


ANOVA results showed that there was no significant difference among various categories but minimum thickness values at coronal third were significantly higher than middle and apical third levels (0.05 > P).

Statistical analysis by t-test revealed that there was a significant difference between Type-I and Type-III category at coronal third level, Type-II and Type-IV category at middle third, Type-III and Type-IV at both coronal and middle third levels.


   Discussion Top


It is a well-established fact that the prevalence of C-shaped canals is race dependent and more common in Asians. Although this canal variant has been reported to range from 2.7% to 8% in mixed populations [1],[7],[13] and 4.7-34.6% in Asian ethnic groups in the mandibular second molar, [4],[14],[15] a few studies are available in literature illustrating the canal anatomy of this particular tooth from Indian population which is hybrid of several ethnic groups with characteristics of Caucasian, Mongoloid and Negroid races (Dravidian group). [2] Therefore, the present study evaluated the root canal anatomy of C-shaped canal system in mandibular second molars collected randomly from Indian population.

Previous studies have reported that there are chances of C-shaped canal system in teeth having fused roots and longitudinal groove. Sutalo et al. in their study have reported that C-shaped canals occurred in 42.9% of their sample of 14 fused mandibular second molars. [16] In the present study, presence of C-shaped canal system was observed in 78.5% of the total number of 42 mandibular second molars with fused roots. The highest prevalence of C-shaped canal configuration observed in this study belonged to Type-II followed by Type-III, Type-IV and Type-I category, which was close to the results obtained by Min et al. [17] and Fan et al. [12]

It has been shown that the prevalence of detection of additional canals increased to 93% with an experienced clinician working on an operating microscope. [18] Matherne et al. in their study have reported the superiority of CBCT over other diagnostic methods and suggested the simultaneous use of the operating microscope and CBCT. [19] Although µCT has been compared to CBCT and reported to be more precise with up to 2 µm resolution, [20],[21] however, the limitations include amount of time required and its usage restricted to only ex vivo studies. [22],[23] Accuracy of CT imaging is well-documented. [24] Major advantages of CBCT over conventional CT scans include X-ray beam limitation, [25] rapid scan time [26] and effective dose reduction. [27] The approach offers a non-invasive reproducible technique for 3D assessment of root canal systems and aids the clinician to visualize the internal anatomy precisely. [28] Furthermore, use of this technique has been firmly advocated in the recent past for diagnosis of root canal aberrations. [29] Hence, 3D imaging may be an interesting method for the study of canal configuration of the C-shaped teeth and in general for the teeth with morphological anomalies. [30] However, CBCT makes use of ionizing radiation. Therefore, it is advised to keep the patient's exposure to radiation as low as reasonably achievable. [31] In view of the above, the simultaneous use of operating microscope and CBCT was preferred to analyze the specimens.

A study by Weine et al. suggested the role of placing K-files in the canals to determine canal configuration of the mandibular second molar. [32] Jerome in the year 1994 supported the fact that deep orifice preparation and careful probing with small files may facilitate a more accurate characterization of the C-shaped canal system. Present study design also explored the canal anatomy below the orifices through insertion of small files.

There were a total number of 100 initial files inserted in 86 orifices of various shapes, which is in accordance with the fact that number of canals below the orifice varies from coronal to apical level in C-shaped canal system. However, in a study by Fan et al., [12] a total number of 132 initial files could be inserted in 83 orifice. The difference could be attributed to various factors such as age changes in the pulpo-dentinal complex, sample source, size and method of examination.

It was observed that a total of four canals were missed completely (2 in Type-I, 1 each in Types-II and IV) mainly due to dentin fusion or calcification which prevented the initial files from entering the canals. Although, bifurcation of canals was the main reason behind the partially missed canals specially at apical third region, one specimen showed merging of canals immediately below the orifice in coronal third level and represented as partially missed canal in Type-II configuration. This explained the reason of insertion of 23 initial files in 24 mesial orifices in the same category. Majority of the partially missed canals were detected at apical third level which suggests that clinically it is more difficult to clean, shape and obturate this area in C-shaped canal system. Employment of various methods such as use of sonics and ultrasonics, light activated disinfection, careful exploration by extravagant use of small files may help in achieving more success in such cases.

Clinically, it is extremely important to perform root canal instrumentation cautiously during treatment as a lot of variation and anatomical diversity pertaining to the shape and thickness exist at each level in teeth with C-shaped canal system. One should be aware of these danger areas so as to avoid the perforation during treatment of such canal system. The lowest values of mean thickness obtained in the present study belonged to Type-III category at different levels and in apical region for all categories which suggests that teeth with Type-III category and apical region are at a risk of strip perforation.

Caputo and Standlee suggested that there should be at least 1 mm of sound tooth substance present around a post in order to resist root fracture. [33] The mean of values obtained in this study for all types was less than 1 mm at middle and apical regions. Hence, a root canal post is not advisable for such a root canal system. A "corono-radicular" amalgam, preferably dentin-bonded, or resin composite might be a better choice as the core or as the final restoration for C-shaped canal system. [34]


   Conclusion Top


The present study revealed anatomical variations of C-shaped canal system in mandibular second molars. Clinically, when a C-shaped canal system is observed, one cannot assume that such a shape continues throughout its length. The prognosis of such complex canal anatomies can be improved by simultaneous use of sophisticated techniques such as surgical operating microscope and CBCT. More studies in future are required employing various other techniques to develop effective methods to clean and shape such canal system.

 
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Correspondence Address:
Sanjay Chhabra
Department of Conservative Dentistry & Endodontics, Army Dental Center (R&R), Delhi Cantonment, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0707.131785

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