Cone-beam Computed Tomographic Analysis of C-shaped Canals and Radicular Grooves in Mandibular Premolars: Prevalence and Related Factors

INTRODUCTION

Morphological variations of root canal systems can be a challenge for root canal cleaning, shaping, and obturation, which may imperil the endodontic treatment outcome. Endodontic management of C-shaped anatomy is an interesting and challenging procedure and its success depends on individual skills and techniques applied.

In the past two decades, the literature has reported the C-shaped root canal anatomy in both maxillary and mandibular molars and premolars. According to slowey, mandibular premolars possess the greatest anatomical challenges with respect to accomplishing successful treatment outcome during root canal therapy.¹ C-shaped canal system is associated with fins and isthmus connecting individual canals, which would change the cross-sectional canal morphology from orifice to apex. It may leave dead space and increase the difficulty during root canal treatment. The C-shaped anatomy gives rise to radicular groove (RG) in mandibular premolars, which result in the C-shaped root cross section.² Clinically, they may act as a reservoir for dental plaque and calculus, increasing the difficulty for the management of periodontal disease.

Recently, CBCT has been used as a reliable aid in the identification of root canal system configurations with superior sensitivity relative to two-dimensional radiographic modalities. Differences in gender and bilateral prevalence of anatomic variations can be compared easily on in vivo CBCT images because of their certain identification of tooth position and study subjects.³

The literature lacks detailed data of anatomy of mandibular premolars based on geographic and ethnic patterns especially in African, Australian, Asian, and South American populations. Presently, there is very limited information regarding the true prevalence of the C-shaped canals and RG in mandibular premolars. Till now, no such work has been carried out in Saudi population using cone-beam computed tomography (CBCT). Hence, in this research, the primary outcome was to evaluate the prevalence of C-shaped canal configurations and RG in mandibular first and second premolars using CBCT in Saudi subpopulation. The secondary outcomes were correlating it with other factors like age, sex, unilateral, and bilateral prevalence.

MATERIALS AND METHODS

STATISTICAL ANALYSIS

Data analysis was performed with the help of the Statistical Package for Social Sciences Version 22 (SPSS Inc., Chicago, IL, USA). Differences in the prevalence of the C-shaped canal and RG based on sex, age, and bilateral prevalence were compared using the Chi-square test with a level of significance as p < 0.05.

RESULTS

An analysis of 156 cases was carried out initially. A total of 34 cases were finalized having C-shaped and 24 cases for RG.

DISCUSSION

C-shaped root canal system of mandibular premolars is a complex anatomy and endodontically challenging. It is characterized by the presence of isthmus, fins, and root canals merging.⁵ Identification of C-shaped anatomy is more challenging as it presents itself as a single oval canal in cervical third predominantly and the C-shaped anatomy begins at the middle third.⁶

CBCT imaging has outperformed regular radiography in terms of its ability for detecting and interpreting aberrant root canal morphology.⁷ It has the advantage of a significantly lower radiation dose with a higher resolution. This study required CBCT scans of patients without exposing them to radiations. Hence, we accessed an already existing database in oral and maxillofacial radiology department.

C-shaped canal configuration is believed to be due to failure of Hertwig’s epithelial root sheath to fuse during the tooth development or coalescence by the continuous cementum deposition. A gene located on chromosome 5 in mice has also been reported to be the most likely candidate gene to cause C-shaped roots.⁸ Patients with X-linked human inherited diseases also showed increased additional root formation in mandibular premolars, suggesting that the genetic change on X chromosome may be a factor contributing to the C-shaped root formation.⁹ These complex anatomic inconsistencies may expand the difficulties amid endodontic treatment.

In this study, we used Fan et al. classification⁶ based on micro-computed tomography to describe the C-shaped anatomy. He described C-shaped root canal as a cross-sectional root canal system presenting a continuous “c” with no separation or division (C1); a canal shape resembling a semicolon resulting from a discontinuation in the “c” outline (C2); two separate round, oval, or flat canals (C3); and only one round, oval, or flat canal (C4).

In general, the prevalence of C-shaped root canal morphology in mandibular first premolars is reported to range from 1.1% to 18%.^10–12 Alkaabi et al. found 28% prevalence of C-shaped canal in an Emirati population.¹³ We found a significantly higher prevalence (17.4%) in mandibular first premolars than as compared to mandibular second premolars (7.4%). C-shaped root canal morphology in mandibular second premolars is reported to be rare.¹¹ Their prevalence seems to have a smaller variation among different populations, perhaps due to the very low prevalence.^11,12

The results of the present study showed a high prevalence (12.5%) of mandibular premolar C-shaped anatomy in Saudi subpopulation. The variations in results might be attributed to different ethnic groups, study design, sample size, and method of inspection.

During the serial axial CBCT image examination, we found that C-shaped canals could change to C1, C2, and C3 from the middle and apical third. Eighty-eight percent of canals were C4 type in cervical third and a high prevalence of C2 type was found in middle and apical third (68.6% and 31.3%, respectively). Our results are in line with previous studies done by Fan et al. and Ordinola-Zapata et al.¹⁴ who via microcomputed tomography stated that the coronal third presented mainly cross-sections with one single round or oval root canal. The more complex C1 and C2 configurations were present mainly in the middle third, whereas the apical section had a majority of C2 or two independent oval or round root canals.

We used the classification of RG given by Fan et al.⁴ dividing them into deep and shallow grooves. A “deep groove” was defined as the depth of the groove exceeding one-third of the bucco-lingual or mesio-distal dimension of the tooth. Whereas the other grooves were classified as “shallow grooves”. We found prevalence of 8.8% for RG. Our results are lower as compared to other studies which might be attributed to the fact that prevalence of RGs shows ethnic predilection.^5,12,15 In the present study, most of the RG were found on mesiolingual surface of the root. Our findings are in agreement with Lu et al.¹² who found RG on the proximal lingual area of the middle root which did not always extend to the root apex.

For both C-shaped canal and RG, we did not find any significant difference between sex, but it was significantly higher in the age group of <50 years. In younger patients during tooth development, the irregular fusion of the Hertwig’s epithelial sheath was attributed to trauma, such as radiation or chemical interference, but following the documentation of racial predilection, it is more likely to be of genetic origin.^16,17 The root canals in such teeth merge in a very wide, slotlike, single, continuous root canal morphology, which can assume the shape of a letter C.¹⁸ We found bilateral prevalence of 14.7% for C-shaped canals and 11.5% for RG which varies according to different racial populations investigated.

In this study, there were some limitations. First, only high resolution CBCT images were considered for analysis. Second, the teeth with exclusion criteria like obturated canals, open apices, calcified canals, and presence of artifact images which could interfere with the correct analysis were not analyzed. These excluded samples were uncommon and a large sample size would have minimized its effect in the final prevalence results. Third, the results may vary based on ethnicity, study design, and sample size.

CONCLUSION

The clinician must be careful to avoid strip perforation due to vigorous instrumentation in thin roots of C-shaped mandibular premolars. Use of CBCT and dental operating microscope may aid in avoiding it and improving endodontic outcome. The presence of RG dictates a C-shaped root cross section. RG can complicate restorations with posts and root canal instrumentation and obturation. To prevent perforation or root fracture, clinicians should understand the correlation between the isthmus wall thickness and RG depth especially in mandibular first premolars.

AUTHOR CONTRIBUTION

All authors have contributed equally.

REFERENCES

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