A Cone Beam Computed Tomographic Evaluation of Root Canal Variations in Primary Mandibular Second Molars and Permanent Mandibular First Molars in Indian Population - A Retrospective Study

Introduction

The two main etiologic factors for pulp involvement requiring endodontic therapy are dental caries and dental trauma. Pulpotomies in primary teeth are challenging to perform as secondary dentine is continuously deposited throughout the life of deciduous teeth.¹ To preserve the length of the arch and the spatial development of the deciduous teeth, pulpectomy is advised if the dental pulp has become irreversibly inflamed. Endodontic therapy is complicated due to connections involving horizontal anastomoses and connections involving furcations, and also the peculiar inner geometry of the deciduous tooth root and canal system.²

The earliest molars to erupt in the mandible are the first permanent molars and are particularly vulnerable to caries, necessitating pulp therapy.³ The system in root canals and its potential variations in canal numbers and orientation must be well understood to increase the favorable outcome of endodontic treatment.⁴ The procedure of root canal treatment for primary and permanent teeth involves removal of the infected or necrosed pulp tissue, preparation and irrigation, and lastly three-dimensional (3-D) obturation of root canals.⁵ One of the primary reasons for missing canals is the failure to acknowledge the intricate anatomy of canals.⁶

Many procedures were used to analyze canal and root morphology of teeth, such as computerized tomography, clearing technique, radiographs, operating microscope, micro-computed tomography (CT), and macroscopic sectioning.^2,3,7 But these techniques had significant shortcomings as it was possible for the connection involving the pulp and exterior structure and processing of research samples to be lost.3 Currently, thorough three dimensional radiographic examinations are becoming more common since they may help understand the root canal system's anatomy beforehand.⁶

In 1990, Tachibana and Matsumoto created cone beam computed tomography (CBCT), which produced quick and precise three-dimensional radiographic images in endodontics.³ Children are particularly vulnerable to the dangers of ionizing radiation; hence special precautions should be taken to minimize the radiation burden while maintaining a high diagnostic yield.⁸

Hence, this study's objectives included identifying and evaluating the diversity in the quantity and internal morphology of the canals in the roots of primary mandibular second molars (PMSMs) and mandibular first permanent molars (MFPMs), as well as researching the application of CBCT in evaluating root canal morphology.

Materials and Methods

This present retrospective study included CBCT images of 50 PMSMs and MFPMs of children aged between 5 to 10 years.

The sample size was estimated using the G Power Software v.3.1.9.4 considering the effect size to be measured at 81% with 95% confidence interval, power of the study at 80%, and alpha error at 5%. The estimated sample size was 50.

The CBCT images that were made for valid diagnostic reasons were obtained from the institutional database of the Department of Oral Medicine and Radiology of a Dental College and Hospital. Parent consent was also taken. A total of 100 PMSMs and 100 MFPMs were analyzed for various parameters such as the number of roots and canals, and root morphology on both sides. Institutional Ethical clearance was obtained with reference no RRDCH/IEC21/22 before initiating the study. The teeth that required endodontic management with or without periapical lesions, teeth with minimal root resorption, with no congenital or developmental anomalies, and all the images that had best clarity, without any artifacts were included in the study. Teeth with multi-surface carious lesions, restored or fractured teeth, teeth with resorbed roots >1/2 the root length, and those with bone loss were excluded. All the images were assessed by the same operator. No randomization and blinding were carried out.

Radiographic techniques

The CBCT images (coronal and axial sections) were taken by a Scanora 3D machine at 90 kV and 12.5 mA, with a field of view of 60 mm and a voxel size of 0.1 mm. The thickness of the slice was 1 mm and the exposure time was kept as 15 seconds. Scans were taken in accordance with the manufacturer’s recommended protocol and all of the images were recorded with the assistance of a licensed radiologist, with the minimum exposure required for optimal image quality. The lowest possible radiation dose and field were guaranteed. All the images were reconstructed with the help of On Demand software (California, USA) 3D.

Evaluation of the image

To get an optimal visualization, the brightness and contrast of image were adjusted with the software's image processing tool. The images were analyzed for the number of roots and canals per root, and canal changes in the coronal region at the cementoenamel junction.

The evaluation criteria of images were based on the criteria outlined by Ran Yang et al. for PMSMs (Figure 1).²

Variant 1: Two separate roots, one mesial and one distal, each containing a single canal.

Variant 2: Two separate roots, the mesial root contains two canals, while the distal root contains one canal.

Variant 3: Two separate roots, each containing two canals, one in the mesial root and one in the distal root.

Variant 4: Three separate roots; mesial, distobuccal, and distolingual, each containing a single canal.

Variant 5: Three separate roots, the mesial root contains two canals, while the distobuccal and distolingual roots each contain one canal.

Variant 6: Three separate roots, the mesial root contains two canals, the distobuccal root contains two canals, and the distolingual root contains one canal.

Variant 7: Four separate roots, with one canal in each root.

The evaluation criteria for lower first permanent molars in the images were based on the Vertuccis classification (Figure 2).

Type I: A lonely canal extends from the pulp chamber to the apex (1).

Type II: Two separate canals exit the pulp chamber and merge before reaching the apex, forming a single canal. (2-1).

Type III: One canal leaves the pulp chamber and divides into two in the root, then merge to exit as one canal (1-2-1).

Type IV: Two separate and distinct canals extend from the pulp chamber all the way to the apex (2).

Type V: One canal leaves the pulp chamber and divides short of apex into two seperate, distinct canals with separate apical foramina (1-2).

Type VI: Two separate canals exit the pulp chamber, merge within the body of the root, then redivide before the apex, exiting as two distinct canals. (2-1-2).

Type VII: A single canal exits the pulp chamber, divides and then rejoins within the body of the root, and finally redivides into two distinct canals before reaching the apex. (1-2-1-2).

Type VIII: Three separate and distinct canals extend from the pulp chamber all the way to the apex (3).

The Ran Yang variants noted in this study were variants 1, 2, 3 and 5, while the Vertucci types observed in this study were Type I and IV (Figure 3).

Statistical analysis

The study data were analyzed using SPSS version 22.0 [Armonk NY IBM, Corp.,] for Windows released in 2013. The experimental data obtained in this paper were presented as categorical variables. The frequency of the numbers of roots and canals was determined and compared using the Chi-square test, with a significance level set at P <0.05.

Results

Distribution of number of roots present in PMSMs and MFPMs among study subjects showed that 96% had two roots and 4% had three roots. No significant differences were observed in the canal shape and root structures of PMSMs and MFPMs with respect to age and gender.

Mesial root of PMSMs showed two canals in 96% of the cases and a single canal in 4% of cases, whereas the distal root showed one root and two root canals in 62% of cases, one root, and one canal in 34% of cases and two roots and single canal each in 4% of cases.

In our study, 92% of the mesial roots of MFPMs had two canals and 8% had a single canal, whereas 80% of the distal roots had a single distal canal, 16% had two distal canals and 4% had two distal roots with a single canal in each.

The morphology of canals in PMSMs using Ran Yang criteria revealed that 62% were of Variant 3, 30% were of Variant 2, and Variant 1 and Variant 5 were 4% each (Table 1).

In MFPMs, the root canal internal morphology using Vertucci’s criteria revealed that 92% of the mesial roots were Type IV, while 8% were Type I. Among the distal roots, 84% were Type I, 12% were Type IV and 2% had distobuccal and distolingual root each having Type I configuration (Table 2).

Discussion

In deciduous teeth, root canal anatomy had not been studied until 1925.⁹ The presence of necrotic pulp or the unsuccessful outcome of pulpotomy procedures may necessitate endodontic therapy of the root canal system if removal of the tooth is to be prevented.¹⁰ The morphology of canals of human mandibular molars has been widely studied since the 1870s.¹¹ Vertucci evaluated canal number, classification, apical foramina locations, and frequency of apical deltas; however, it did not report on the degree or configurations of the curvatures or if they related to the type of canal classification.¹² Early detection, however, is crucial since successful debridement, instrumentation, obturation, and even final management depend on a thorough understanding of the canal morphology.¹³

The most significant disadvantage of conventional radiography, which is frequently utilized is the overlap of the roots and root canals.^1,2 Three-dimensional radiography techniques may provide a more precise approach for these investigations, according to earlier studies.¹⁴ The advantages of CBCT over traditional CT scans include less radiation exposure, faster scanning and higher resolution.^2,4

In our study, 96% of the PMSMs had two roots while 4% had three roots. This result is comparable to earlier studies, where the majority of the PMSMs were two rooted.^1,15,16 Studies on the prevalence of three-rooted mandibular primary molars in Taiwanese children revealed that 10% of PMSMs were three-rooted based on bite-wing radiographic analysis.¹⁷ However, another study analyzed the prevalence of three-rooted PMSMs using CBCT and reported 27.52% prevalence in Chinese children which agrees with the findings of a study conducted in a Korean population (27.8%) using digitalized periapical radiographs.^2,18

In the current study, 96% of the mesial roots of PMSM had two root canals, while a single canal was found in 4% of the cases. In contrast, one root and two root canals were found in 62% of the distal root cases, one root and one canal in 34% of the cases, and two roots and a single canal each were found in 4% of the cases. These results conform with the study where most of the PMSMs (97.74%) had two root canals in the mesial root and the others had only one canal, while in the distal roots, 34% had one canal, 65.9% had two canals and all of the PMSMs that had two distal roots had one canal in each of the distal root except in three teeth, which had two canals in the distolingual root.² Also, a study reported that 100% of the mesial roots and 53.3% of the distal roots had two canals, and 40% of the distal roots had one canal.¹⁵ In another study, 86.67% of the mesial roots of two-rooted mandibular second molars showed two canals, whereas four molars showed a single canal in the mesial root. Distal root of two-rooted molars in 77.78% of teeth had two canals and the remaining 22.22% had a single canal.¹⁶ However another study reported that 100% of the mesial roots and 100% of the distal roots of the studied teeth had two canals.¹⁹ In another study, 100% of the mesial roots and 36.4% of the distal roots had two canals, and 63.6% of the mesial roots had one canal which is in contrast with our study findings.¹

In our study, among the PMSMs studied, Variant 3 as per Ran Yang’s classification was the most common (62%) configuration, followed by Variant 2 (30%), Variant 1 (4%), and Variant 5 (4%) (Table 1). Similar findings were observed in a study where Variant 3 (47.64%) was the most typical configuration seen followed by Variant 5 (25.46%) and Variant 2 (23.82%).² In another study, Variant 2 (63.6%) was reported to be more common than Variant 3 (36.4%).¹

In this study, among the lower first permanent molars, 96% were two-rooted and 4% were three-rooted. This finding conformed with the study which reported 96.8% of lower first permanent molars as two-rooted and a third root was diagnosed in 3.2% teeth.⁴ A study done on the Burmese population showed 90% two-rooted and 10% three-rooted MFPMs.²⁰ Similar results were found in the subsequent studies conducted.^11,21-24 Whereas the studies with contrasting results reported three-rooted MFPM in 31.4% and 31.97% cases.^14,25

In our study, in the mesial root, 92% of MFPMs had two canals and 8% had a single canal, whereas in the distal root, 80% had a single distal canal, 16% had two distal canals and 4% had two distal roots with one canal in each. Similar results were reported in multiple studies conducted.^4,20-22,26 Overall, 72% of the specimens had three root canals, 20% had four root canals and 8% had two root canals. Another study also found three canals in 61.3% teeth and 35.7% teeth had four canals.²⁶ However, another in vitro study done on MFPMs in Sudanese inhabitants concluded that 59% of distal roots had two canals and 38% of distal roots had a single canal each, which is contrasting with the present study findings.²⁷ Varying from our findings, research on MFPMs in a Kuwaiti population found that, overall, 51% of the distal roots had one canal and 49% had two canals.¹⁹

In the current study, among the MFPMs, 92% of the mesial roots were Type IV as per Vertucci's classification, 8% were Type I and 80% of the distal roots were Type I, whereas 16% were Type IV and 4% had distobuccal and distolingual root each with Type I configuration. Vertuccis Type IV configuration (92%) was the most common in the mesial roots and Type I configuration (80%) was most common in the distal roots (Table 2). This result is in line with the findings of following studies.^{3,21-23,25,26} However, a study found that Vertucci Type II was the most common configuration in the mesial root, while Type III was the most common in the distal root.⁴ Additionally, a research conducted on American population revealed a widely diverse mesial root canal morphology, with Type V configuration being the most frequently seen form.²⁸

The rarity of reports of unusual root patterns in primary teeth may be due to the short window of time between their formation and resorption, also the fact that in many instances, in extracted primary teeth, the unusual root pattern is not noticeable because root resorption has already occurred.²⁹

In comparison to conventional radiographs, 3D imaging of primary molars may offer greater clues and interpretation of changes in the canal morphology of roots, which would increase dentists' ability to interpret the images for accurate diagnosis.³⁰ So, Paediatric dentists ought to be equipped with the understanding of the root canal internal morphology in deciduous and young permanent teeth for the overall success of the treatment plan in children.

Clinical Significance

Since there is a four percent probability of discovering an additional distal root in our study, the practitioner should be mindful of this possibility while performing pulp treatment in primary teeth. For better detection and access to the roots in the PMSM, appropriate straight-line access preparation and position of the extra distolingual root canal opening often require modification of the trapezoidal form. Additionally, since our investigation identified several complex root canal variations, a more thorough understanding of the differences in root and canal anatomy is essential to enhance the outcomes of endodontic therapy.

The preparation of permanent molars with curved canals and other abnormalities in the root canal system could likely be accomplished with nickel-titanium rotary devices, although these have a propensity to break in specific clinical circumstances. To prevent buckling and instrument separation in such circumstances, hand files should be used before using rotary files. Also, by being aware of the differences, the likelihood of missed canals and consequent need for endodontic re-treatment can be reduced to some extent. By knowing morphologic variations in the canal, proper access cavity designs and proper instrumentation can be effectively chosen in endodontic procedures.

Limitations

Due to its technique sensitivity, high cost, and limited accessibility, CBCT cannot be used in all cases to evaluate root canal morphology, unless there are additional anomalies present, such as extra teeth, malignancies, or facial fractures.

To better understand the variations in root canal morphology within the Indian population, additional research with a larger sample size is needed, given the limitations of the current study’s sample size.

Conclusion

This in vitro study revealed variations in the morphology of roots and canals in PMSMs among children. To successfully treat primary teeth with root canal treatment, one may need more information than just the potential number of canals. Therefore, understanding the different root canal configurations in primary teeth enhances the likelihood of successful treatment in a pediatric clinic.

Financial Support And Sponsorship

The authors have no funding to report

Conflict of Interest

Nil