Frequency of Multiple Canals in Mandibular Premolars and its Correlation with Other Anatomical Variants (C Shaped Canals in Mandibular Second Molars): A Retrospective and Cross-sectional Study

Introduction: Recognition of variations in molar root morphology is critically important for dental procedures such as root canal treatment and apical surgery. Usage of CBCT enables systemic evaluation of teeth including the number of roots and canals, location of roots, etc. The aim of this study was to determine the frequency of multiple canals in mandibular first and second premolars and to evaluate correlations between other anatomical variants using Cone beam computed tomography (CBCT). Methodology: Images of mandibular premolars obtained from CBCT images in the axial, coronal, and sagittal planes were reconstructed using GALILEOS Comfort PLUS ( Sirona 3D)is an advanced CBCT that provides seamless workflow integration. Serial axial, coronal and sagittal-plane CBCT images were closely examined at 1.0-mm intervals from the canal orifice to the apex. SPSS chi-squared test for different Various anatomical distolingual roots of first molars, C shaped canals of second molars are highly correlated with different canal configurations of mandibular premolars. Conclusion: This retrospective study showed that different configurations of mandibular premolars canals was significantly correlated with the presence of Distolingual root (DLRs) in first molars, and C shaped canals in second molars. Understanding and identifying anatomical variants is important in comprehensive success of endodontic treatment.


INTRODUCTION
Recognition of variations in molar root morphology is crucial for dental procedures such as root canal treatment and apical surgery. Adequate knowledge regarding anatomical variants of canal helps in achieving success in root canal treatment [1,2]. Mandibular premolars are known as enigma to endodontists as it exhibits enormous variations in canal morphology [3,4]. "Previous studies have shown high frequencies of multiple canal systems in mandibular premolars (12.9-34.8% and 2-9.9% in mandibular first and second premolars, respectively). These variations are caused by differences in methodology, ethnicity, and characteristics of participants, such as age and gender" [5,6].
"Permanent mandibular first molars usually have 2 roots, mesial and distal. Later, a third root, distolingual (DL) root, develops in a number of individuals. Literature reviews have shown the high prevalence of 3-rooted mandibular first molar from 5% to more than 40% in Asian populations" [7][8][9][10]. Therefore, it would be advantageous for CBCT usage in many treatments.
"In the routine diagnostic periapical radiograph, the X ray cone tube is placed perpendicular to the mandibular first molar and the film. Therefore, the image of the DL root is easily super-imposed by the distobuccal (DB) root, and it is unclear." [1,11] "Recently introduced Conebeam computed tomography (CBCT) is designed for dental use and serves as noninvasive and 3dimensional reconstruction imaging. CBCT images can be used to evaluate morphologic analysis of the DL root of the permanent mandibular first molars" [12,13]. "In apical surgery, the use of CBCT enables systematic evaluation of teeth in all manners. Previously, our team had a rich experience in working on various research projects across multiple disciplines" [14 -28]. Now the growing trend in this area motivated us to pursue this project.
The goal of this research was to determine the frequency and morphologic characteristics of multiple canals of mandibular first and second premolars using Cone beam computed tomography (CBCT).

Study Design
The protocol of this retrospective, cross-sectional study was approved by the Ethics Committee of Saveetha Dental Hospital, Chennai, India. Images of mandibular premolars were obtained from patients who had undergone CBCT scanning at the hospital between January 2018 and November 2020. CBCT images were acquired with the following parameters: 80 kVp, 9.0 mA, 10 × 10-cm field of view, 0.167-mm3 voxel size, and the slice thickness was 1.0 mm.

Sample Size
100 patients were examined in vivo by CBCT. The inclusion criteria applied were the patients aged between 18 and 70 years; presence of mandibular premolars with fully matured apices and without apical periodontitis; presence of mandibular premolars without root canal fillings, posts, and crown restorations, patients undergoing orthodontic treatment and patients with calcified canals. The Vertucci classification and the Fan classification will be used to define root canal configurations and C-shaped canals, respectively. In a logistic regression study, the connection between non-single canals in PM1s and DLRs in M1s was employed.

Image Assessment
Cross-sectional images in the axial, coronal, and sagittal planes were reconstructed using GALILEOS Comfort PLUS ( Sirona 3D). Implant surgery or surgical removal of impacted molars were the most common reasons for CBCT scans.
As a result, no subjects in this study were subjected to excessive radiation in order to gather information about root canal anatomy; also, the "as low as reasonably achievable" principle was applied to radiation dose. To avoid any possible bias, data were anonymised by numbering the participants from 1 to 300 before examining the images.
Axial-plane images were used to determine the number of roots in premolars. Single-rooted teeth, such as teeth with two canals and a fused root, had conical-shaped roots. Teeth with two canals in a single fused root and a third canal in a separate root showed bifurcation at a particular root level, as did teeth with two canals in a single fused root and a third canal in a separate root. Teeth with three independent roots were known as triple-rooted teeth. C-shaped canal configurations were determined in accordance with the Fan classification as follows: C1 (continuous C-shaped canal: an uninterrupted "C" without separation or division); C2 (semicolon-shaped canal: caused by discontinuation of the "C" outline); C3 (separated canals: two or three separate canals); C4 (a single canal subdivided into round (C4a), oval (C4b), or flat canals (C4c)); C5 (≥3 separate canals); or C6 (no visible canal lumen) [29].

Statistical Analysis
Statistical analyses were performed using SPSS software (ver. 21; SPSS, Inc., Chicago, IL, USA). The chi-squared test was performed for analyses of differences based on sex, and premolar canal configurations. The chi-squared test was also used to compare the frequencies of disto lingual roots in first molars and C-shaped canals in second molars according to premolar root canal configuration and to compare unilateral and bilateral molar DLRs and C-shaped canal configurations.
The respective frequencies of DLRs in first molars and C-shaped canals in second molars were 28.4% and 32.8%. Chi-squared analysis revealed that the frequency of molar DLRs varied significantly according to premolar root canal configuration (p <0.05).

DISCUSSION
"The primary goal of endodontic treatment often got vulnerable because of the complexity of the root canal anatomy and lack of its knowledge and clinical challenges raised because of it. Thus, for any endodontic therapy, one must precede with a thorough knowledge of pulp chamber and root canal configuration and number of canals as the success of the therapy is directly related to the elimination, prevention of microbial contamination, and complete disinfection by the proper endodontic procedure" [30,31].
"The mandibular first molar is the first posterior tooth that erupts in the oral cavity and frequently requires root canal treatment. This tooth has two roots, but occasionally, it has three roots with two or three canals in the mesial root and one, two, or three canals in the distal root. Over the years, there have been numerous reports that described the morphology of teeth including mandibular first molar" [32,33]. The major variant in this group is the mandibular molar with five, six, and seven canals. According to Martinez-Berna and Badanellis, who reported a mandibular molar with six canals, three in the mesial root that were independent throughout the root and three canals in distal root with independent orifices in the pulpal floor but join immediately to form two canals. Ghoddusi et al. also reported "a mandibular molar with four distal canals. The intracanal communication frequency is higher in the mesial root of mandibular molars which make the variant morphology and so the disinfection more difficult to achieve. Cohen and Burns described maxillary first molar as "The most treated, but least understood posterior tooth with the highest endodontic failure rate." It reported that many treatment failures in the maxillary permanent first molar were related to the inability to locate and clean the MB canal" [34,35].
"The significance of advanced diagnostic tools such as dental operating microscope (DOM) and cone-beam computed tomography (CBCT) over the traditional diagnostic tools has been proven by various researchers till now. CBCT assists the practitioner to identify canal morphology, numbers of canals, and relative positioning even in the presence of calcific metamorphosis and dystrophic calcifications. Identification and treatment of lateral canals are supported by viewing their specific location with the use of narrow field of view CBCT before or during endodontic therapy" [36,37].
"The C-shaped canal configuration presents with variations in both the number and location of the canal(s), as the canal(s) courses from the coronal to the apical third. The complexity of this canal configuration proves to be a challenge with respect to debridement and obturation, and possibly the prognosis during root canal therapy.
Recognition of a C-shaped canal configuration before treatment can facilitate effective management, which will prevent irreparable damage that may put the tooth in severe jeopardy." [38,39] "The C-shaped canal configuration shows an ethnic predilection. It has frequently been reported in countries belonging to the Asian continent. East Asian population groups like the Chinese (0.6%-41.27%) and Koreans (31.3%-45.5%) display a high prevalence of this variant. Among the South Asian countries, Burmese population showed a prevalence of 22.4%, which was much higher than the Indian, Thai or Sri Lankan population.
Higher incidence of C-shaped anatomy was documented in Lebanese population (19.1%) as compared to the other West Asian population groups (Iranian, Jordanian, Saudi Arabian)" [39,40].
"The frequency of first premolars with a single canal (760 of 971, 78.27%) was comparable to those reported in two systematic reviews (75.8 and 73.55%) as well those reported in East Asian populations (e.g., Chinese and Taiwanese [65.2-87.1%]). Regarding the root canal morphology of second premolars, a recent review reported a markedly lower incidence of a second canal (2%) in East Asian populations compared with other populations. Our institution is passionate about high quality evidence based research and has excelled in various fields" [18,[41][42][43][44][45][46][47][48][49][50] The thorough knowledge of root canal space anatomy is a basic prerequisite for the successful completion of endodontic treatment, especially in cases where extra root canals are suspected. Proper care and attention must be given in identifying extra roots and canals.

Graph 1. Canal Variations in Mandibular Premolars and Molars
The graph represents the correlation of anatomical variants such as distolingual roots of first molars, C shaped canals of second molars with canal configuration of mandibular premolars

DISCLAIMER
The products used for this research are commonly and predominantly use products in our area of research and country. There is absolutely no conflict of interest between the authors and producers of the products because we do not intend to use these products as an avenue for any litigation but for the advancement of knowledge. Also, the research was not funded by the producing company rather it was funded by personal efforts of the authors.

CONSENT
As per international standard or university standard, patients' written consent has been collected and preserved by the author(s).

ETHICAL APPROVAL
As per international standard or university standard written ethical approval has been collected and preserved by the author(s).