Location angle of second mesio-buccal canal in maxillary molars of an Indian population: an in vivo retrospective CBCT evaluation and proposal of a new classification

Introduction

The inability of clinicians to recognize the heterogeneity of root canal therapy and to locate every canal in the tooth is one of the main causative factors for the failure of the therapy (Lee et al., 2020). Understanding the anatomy of the tooth structure and the root canal system in depth is essential to the success of the treatment (Akbarzadeh et al., 2017). Thorough knowledge is obligatory because every tooth is unique anatomically, having a different number of canals and roots and variation in the presence of the location of the canals in maxillary molars (Kewalramani, Murthy & Gupta, 2019).

The literature reveals that, during the root canal treatment of the maxillary molars, locating all canals is often missed by clinicians (Kewalramani, Murthy & Gupta, 2019). They have a minimum of three roots (mesiobuccal, distobuccal and palatal roots) and a maximum of up to four roots (Cantatore, Berutti & Castellucci, 2006). However, studies have shown that one or two roots can occur in maxillary molars (Mashyakhy et al., 2019; Al Mheiri et al., 2020). There are even claims of these teeth comprising five roots (Barbizam, Ribeiro & Filho, 2004; Borghesi et al., 2019). Each root exhibits unique internal anatomical variations in terms of shape, form, and size. However, the mesiobuccal (MB) root is perpetually believed to present an anatomical and clinical challenge. This is in accordance with the retreatment cases observed by Cleghorn, Christie & Dong (2006), where approximately 93% of cases failed due to missed canals in MB roots. Furthermore, they affirmed the presence of two or more canals in the MB root in approximately 56.8% of cases.

There are various ways to study root canal anatomies (Naseri et al., 2018; Kewalramani, Murthy & Gupta, 2019; Mashyakhy et al., 2019; Al Mheiri et al., 2020). Laboratory studies employ a wide range of methods to study root canal anatomy, including decalcification with injection of India ink, Chinese ink, hematoxylin dye, plastic, or metal castings, in vitro endodontic access with radiography and instruments or instruments only, in vitro radiopaque gel infusion and radiography, in vitro root canal treatment (RCT), in vitro radiography, in vitro macroscopic examination, scanning electron microscope examination of pulp floor, grinding or sectioning and, most recently, cone-beam computed tomography and microcomputed tomography (Ahmed, 2022). The clinical methods encompass retrospective analysis of patient records, radiography of all teeth, in vivo radiographic examination, and clinical evaluation during endodontic treatment using magnification or a dental operating microscope (DOM) or during endodontic treatment where magnification was not specified (Cleghorn, Christie & Dong, 2006).

In the past few years, scientific advancement has resulted in a significant reduction in the dose of radiation generated by the latest-generation devices, allowing for increasingly high-resolution diagnostic exams and applications in every branch of dentistry. Furthermore, the possibility of using ionizing-radiation-free diagnostic exams in dentistry has led to scientific research in this area yielding interesting results that inspire confidence. Assessments of this method, in addition to providing useful diagnostic indicators, could be used with absolute credibility for patient follow-up because they can be repeated over relatively short distances without exacerbating biological damage (Reda et al., 2021).

It has been suggested that approximately 96.1% of maxillary molars indeed have a second mesiobuccal canal (MB2) in the American population (Blattner et al., 2010). In the Indian population, the distribution of MB2 canals in maxillary first molars ranges from 61.9% to 86.36% (Kewalramani, Murthy & Gupta, 2019; Shetty et al., 2017). The supporting in vitro and in vivo studies of MB canal variation are summarized in Tables 1 and 2. There has been competent literature on the incidence of a second mesiobuccal canal; however, lacunae exist regarding the actual location of this type of canal in any population. Most of the studies concentrate on the incidence of MB2 and/or the MB1–MB2 canal distance (Lee et al., 2020; Akbarzadeh et al., 2017; Cotton et al., 2007; Tuncer, Haznedaroglu & Sert, 2010; Huumonen et al., 2006) but rarely measure the angles between the canals, which may help to depict the actual location.

With the above background, the current study aimed to (i) assess the location of MB2 canals with respect to the disto-buccal canal and palatal canal in the maxillary molars, (ii) measure the angles and distances between the canals using CBCT images in an Indian population and (iii) devise and employ a classification based on information gleaned from an examination of the angles between the DB-palatal and MB1–MB2 lines.

Materials and Methods

Results

The parametric observation was achieved by marking the x- and y-axes. The y-axis is the imaginary line passing through MB1. This imaginary line is parallel to the line connecting the DB-P canal. The MB1–MB2 mean distance is assumed to equal the highest y-axis value and the zero point (Fig. 2).

$\mathrm{X}=(\mathrm{M}\mathrm{b}1\cdot \mathrm{M}\mathrm{b}2\mathrm{d}\mathrm{i}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e})\times \mathrm{s}\mathrm{i}\mathrm{n}\alpha$

$\mathrm{Y}=\mathrm{M}\mathrm{e}\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{i}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}-(\mathrm{M}\mathrm{b}1\cdot \mathrm{M}\mathrm{b}2\mathrm{d}\mathrm{i}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e})\times \mathrm{c}\mathrm{o}\mathrm{s}\alpha$

Angle between MB1–MB2 and DB-P canals maxillary first molar

In the 81 maxillary right first molars, the prevalence of MB2 was highest in the positive angle >4° exhibited by 36 teeth, followed by the positive angle 0.1° to 1.9° in 19 teeth and the positive angle 2° to 4° in 17 teeth. These teeth also exhibited negative angles (−2° to −4°) in 5 teeth, (>−4°) in 3 teeth, and (−0.1° to −1.9°) in 1 tooth (Fig. 3).

In 81 maxillary left first molars, the prevalence of MB2 was highest in the positive angle >4° exhibited by 31 teeth, followed by the positive angle 2° to 4° in 24 teeth and the positive angle 0.1° to 1.9° in 15 teeth. These teeth also exhibited negative angles (−2° to −4°) in 6 teeth, (>−4°) in 4 teeth, and (−0.1° to −1.9°) in 2 teeth (Fig. 4).

Angle between MB1–MB2 and DB-P canals maxillary second molar

In 81 maxillary right second molars, the MB2 prevalence was highest in the positive angle 2° to 4° exhibited by 32 teeth, followed by the positive angle >4° in 23 teeth and the positive angle 0.1° to 1.9° in 14 teeth. These teeth also exhibited negative angles (−2° to −4°) in 8 teeth, (>−4°) in 4 teeth, and no tooth exibhited (−0.1° to −1.9°) (Fig. 5).

In the 81 maxillary left second molars, the MB2 prevalence was highest in the positive angle 2° to 4° exhibited by 36 teeth, followed by the positive angle >4° in 26 teeth and the positive angle 0.1° to 1.9° in six teeth. These teeth also exhibited negative angles (−2° to −4°) in 8 teeth, (>−4°) in five teeth, and none of the teeth were present (−0.1° to −1.9°) (Fig. 6).

Application of BVP’s angular classification

The location of MB2 after application of BVP’s angular classification is represented in Figs. 7A–7F.

Discussion

The anatomical morphology of roots and the canal of teeth vary to a high extent. The frequency of missed canals is solely because of morphological variation of canals in the tooth root. It is assumed that there are two or more canals in the MB root (Cantatore, Berutti & Castellucci, 2006).

In the current study, CBCT technology was selected to assess the location of the MB2 canal in maxillary molars. The usage of CBCT for canal detection is a practical method. It is one of the reliable diagnostic methods for detecting and studying anatomical variation presented in an individual (Alfouzan et al., 2019; Martins et al., 2018). In computed tomography, anatomical structures such as teeth and their neighboring structures are seen in three planes (Olczak & Pawlicka, 2017).

CBCT provides quite favorable results and has upgraded the ease and possibility of reading otherwise missed MB2 canals during the procedure. It is advantageous over other diagnostic measures, as it is noninvasive and thin slices permit adequate visualization without distortion of the image (Agwan et al., 2015; Nikoloudaki, Kontogiannis & Kerezoudis, 2015). The teeth excluded in the present study were those with metal posts, root canal treatment or rehabilitation cases with fixed prostheses. These types of subjects were excluded to ensure scatter-free images owing to their higher density nature (Betancourt et al., 2016). Because of the exposure period, the radiation dosage for CBCT is dependent on the voxel resolution. The higher the voxel size is, the greater the acquisition needed; therefore, the radiation exposure increases. CBCT has good sensitivity and specificity for the diagnosis of MB2 (Betancourt et al., 2015). It helps practitioners perform a safe, effective, and predictive endodontic treatment (Stropko, 1999; Hofmann & Thorpe, 2002; Vizzotto et al., 2013).

However, dental professionals should also follow the ALARA principle. The fundamental concepts of radiation dosage exposure justification, optimization, and limiting. The updated and improved CBCT software has enabled upgrading the resolution of images. This leads to greater diagnostic accuracy and precision (Fernandes et al., 2019). The determination of tooth length on CBCT scans was trustworthy and accurate, according to an analysis of dental anatomy using CBCT and conventional periapical radiography (Naseri et al., 2018).

The current study measured the MB1–MB2 canal distance in an Indian population. The presence of the MB2 canal was determined by studying the angles between the imaginary lines. These lines connecting MB1–MB2 and the DB-P canal orifice were considered. The images were rebuilt in this investigation so that the tooth’s long axis was perpendicular to the plane going through the CEJ. The observation plane was positioned 1 mm below the horizontal plane traveling through the pulpal floor. The CEJ was referenced for restructuring the image to allow simple recognizability with highly reproducible results. Clinicians acknowledge the root canal orifice at the pulpal floor after access cavity preparation, which further increases the ease of locating the canal (Lee et al., 2020; Deutsch et al., 2005).

The distance between MB1 and MB2 in the upper 1^st molar was 3.12–3.31 mm, while this distance in the maxillary 2^nd molar was 2.8–3.1 mm (Table 4). Similar results were seen by Sujith et al. (2014) in his study on the maxillary 1^st molar. It was found that the MB2 canal can be located within 5 mm of the MB1 canal (Sujith et al., 2014). The study performed by Lee et al. (2020) on 211 teeth showed that the MB1–MB2 canal distance between the orifices of the first molar was 2.53 mm for the adjacent molar, it was 2.42 mm, both in the unknown population. A similar observation was found in a study with 2.67 mm and 2 mm in maxillary first and second molars (1,100 teeth), respectively (Betancourt et al., 2016). It has been shown that detection of the MB2 canal was more successful if channeling was performed with the help of an ultrasonic tip in the chamber floor, particularly within 3 mm from the MB canal toward the palatal canal (Wolcott et al., 2002).

The present study places more emphasis on the actual location of the second mesiobuccal canal rather than its incidence. The angle studied connecting the lines MB1–MB2 and DB-P canals defines the position of MB2. The angle was read as positive if the MB2 canal was more mesial than the imaginary line parallel to the line linking the DB and P canals going through MB1. When the MB2 canal was further away from the imaginary line, however, the interpretation was negative.

Sixty-seven maxillary first molars showed positive angle III, and sixty-eight maxillary second molars showed positive angle II. Another study was performed by Lee et al. (2020), in which the angles obtained were 2.30° ± 5.70° in the first molar and −3.95° ± 7.73° in the second. The angles between the connecting imaginary lines were within ±8°. Another finding stated that the above mentioned angle was strictly mesial in the first two molars. No such study has been performed by Indian authors thus far.

During endodontic procedures on maxillary molars, clinical practitioners should acquire adequate knowledge of tooth morphology. From the inferences obtained from the study, it can be stated that the most frequent position of MB2 is within 3 to 3.5 mm of MB1. This finding will facilitate easy locating of otherwise missed MB2 canals to ensure adequate success in endodontic procedures for upper molars.

Conclusions

Accurate diagnosis of the location of the second mesiobuccal canal increases the success rate of endodontic treatment and leads to a better prognosis. The classification proposed in the present study further aids in detecting the precise location of MB2 with respect to measurements of distance and angle.

Supplemental Information