EVALUATION OF INCIDENCE OF DISTOLINGUAL ROOT AND

THE INTERNATIONAL JOURNAL OF MICRODENTISTRY98

1 Comprehensive Dental Care, The Nippon Dental University Niigata Hospital, Niigata, Japan

2 Department of Oral and Maxillofacial Radiology, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan

3 Department of Removable Prosthodontics, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan

4 Dental Anesthesia and General Health Management, The Nippon Dental University Niigata Hospital, Niigata, Japan

Correspondence to:

Yoshihiro SugawaraComprehensive Dental Care, The Nippon Dental University Niigata Hospital1-8 Hamaura-cho, Chuo-ku, Niigata, Niigata, JapanE-mail: [email protected]

EVALUATION OF INCIDENCE OF DISTOLINGUAL ROOT AND PREVALENCE IN MANDIBULAR FIRST MOLARS IN A JAPANESE POPULATION WITH CONE-BEAM COMPUTED TOMOGRAPHY

Yoshihiro Sugawara, DDS, PhD1/ Ryo Mizuhashi, DDS, PhD1/ Ichiro Ogura, DDS, PhD2/ Fumi Mizuhashi, DDS, PhD3/ Makoto Oohashi, DDS, PhD4/ Yoshiyuki Minami, DDS2/ Hisato Saegusa, DDS, PhD1

Aims: Since the root canal system of the molars is particularly complex, the success of root canal treatment (RCT) depends on knowledge of its morphol-ogy. A distolingual root (DLR), which is also called radix entomolaris1, is a known type of mandibular first molar; however, its incidence and the prevalence of its treatment have not been elucidated in the Japanese population. The purpose of this study was to determine the DLR incidence in mandibular first molars and the prevalence of RCT in mandibular first molars in the Japanese population on cone-beam computed tomography (CBCT). Material and Methods: A total of 150 patients (male: 53, female: 97; age range: 11-85 years) who underwent CBCT examinations at our hospital between November 2019 and February 2020 were included in the study. Images that captured mandibular first molars (n=171) were continuously extracted. The number of three-rooted mandibular first molars with a separate DLR, history of RCT, and presence of radiolucency at the apex were examined to analyze DLR incidence and the prevalence of RCT. Result: The incidence of DLR was 30.4% (male: 30.5%, female: 30.4%) in this patient cohort. A history of RCT was identified in 34.5% of all teeth; of which 24.6% were char-acterized by radiolucency at the apex. Of the 59 teeth with a history of RCT, 71.2% were treated unsuccessfully, as characterized by the presence of an apical lesion. More specifically, failure of RCT was observed in 47.5% of mesiobuccal (MB) roots, 50.9% of mesiolingual (ML) roots, 50.9% of distal (D) or distobuc-cal (DB) roots, and 70.0% of DLR alone. Conclusions: The results of the present study show that the incidence of DLR in mandibular first permanent molars on CBCT in a Japanese population was 30.4%. The rate of RCT failure characterized by radiolucency at the apex was 71.2%; specifically, failure rates for MB, ML, D or DB, and DLR alone were 47.5%, 50.9%, 50.9%, and 70.0%, respectively. Int J Microdent 2020;11:98–102

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INTRODUCTION

Since the root canal system of the molars is particularly complex, the success of root canal treatment (RCT) depends on knowledge of its morphology. A distolingual root (DLR), which is also called radix entomolaris1, is one of the anatomical variations of mandibu-lar first molars. The incidence of a DLR varies significantly across ethnic groups, with incidence rates of 11.4% in individuals of Mongolian origin, 2.8% in indi-viduals of African origin, and 4.2% in individuals of Caucasian origin2. The incidence is particularly high in the Korean, Taiwanese, and Chi-nese populations, ranging from 22% to 26.1%3-9. In contrast, the incidence is relatively low in the German, Indian, Turkish, and Ira-nian populations, ranging from 0.68% to 8.3%10-15. However, the incidence of a DLR and the preva-lence of its treatment have not been elucidated in the Japanese population. The purpose of the present study was to determine the incidence of radix entomo-

laris in mandibular first molars in the Japanese population and de-termine the success rate of RCT using cone-beam computed to-mography (CBCT).

MATERIAL AND METHODS

Patient population

This retrospective study was ap-proved by the ethics committee of our institution. The images of 150 patients, 171 teeth (male: 53, female: 97; age range, 11-85 years) with DLRs in mandibular first permanent molars examined by CBCT in our university hospital from November 2019 to February 2020 were reviewed.

Image acquisitionCBCT imaging was performed with a CBCT unit (Fine Cube; Yoshida, Tokyo, Japan). The CBCT parameters were as follows: tube voltage, 90.00 kV; tube current, 4.00 mA; field of view, 81×81

mm2; and rotation time, 16.8 s. The protocol was set at a thick-ness of 0.144 mm, resulting in axial, cross-sectional, and par-asagittal MPR images.

Image analysis

CBCT findings of patients with mesiobuccal root canals in man-dibular first permanent molars were independently analyzed by two dentists. Data were recorded with or without a DLR. A history of RCT and the presence of ra-diolucency at the apex (apical le-sion) were examined to determine DLR incidence and the prevalence of RCT (Figs 1 and 2). The chi-squared test was used for statisti-cal analysis.

RESULTS

The incidence of DLR was 30.4% (male: 30.5%, female: 30.4%) in this patient cohort (Table 1). A history of RCT was identified in 34.5% of all teeth (with a DLR: 38.5%, without a DLR: 32.8%);

Fig 1 Mandibular first molar with a distolingual root (red arrows) and vi-tal pulp.



Sugawara et al

of which 24.6% were character-ized by radiolucency at the apex (with a DLR: 32.7%, without a DLR: 21.0%) (Table 2). Of the 59 teeth with a history of RCT, 71.2% (with a DLR: 85.0%, without a DLR: 64.1%) were treated unsuc-cessfully, as characterized by the presence of an apical lesion. More specifically, failure of RCT was ob-served in 47.5% of mesiobuccal (MB) roots (with a DLR: 50.0%, without a DLR: 46.2%), 50.9% of mesiolingual (ML) roots (with a DLR: 50.0%, without a DLR: 51.3%), 50.9% of distal (D) or dis-tobuccal (DB) roots (with a DLR: 60.0%, without a DLR: 46.2%), and 70.0% of DLR alone (Table 3). There was no significant dif-ference as determined by the chi-squared test.

DISCUSSION

The incidence of a DLR varies sig-nificantly across ethnic groups, with an incidence rate of 11.4% in individuals of Mongolian origin2. However, this was determined us-ing periapical radiographs, which likely underestimates the inci-

dence of a DLR compared with CBCT. Studies that used CBCT and multi-detector CT demon-strated a high DLR incidence in the Korean, Taiwanese, and Chi-nese populations, ranging from 22% to 26.1%3-9. In the present study, the incidence of a DLR in the Japanese population was 30.4%, which is relatively high among those of Mongolian origin.

It was also demonstrated that RCT was performed in 34.5% of all teeth (with a DLR: 38.5%, without a DLR: 32.8%); among them, 24.6% were character-ized by radiolucency at the apex (with a DLR: 32.7%, without a DLR: 21.0%) (Table 2). Although the presence of radiolucency at the apex was more common in those with a DLR, there was no significant difference compared to those without a DLR. Radiolu-cency at the apex may be missed when the number of root canals is high or when found at an irregular site. This may have contributed to the high likelihood of finding radio-lucency at the apex in teeth with a DLR.

Systematic reviews have dem-onstrated that the success rates

of initial and secondary RCT were 74.6%16 and 76.7%17, respectively. In Japan, RCT is generally per-formed by general dentists, rather than endodontists, due to inex-pensive insurance coverage. This makes it challenging to ensure sufficient treatment time, which consequently lowers the success rate and likely increases the fre-quency of secondary RCT. In the present study, it was demonstrat-ed that 71.2% (42/59, with a DLR: 85.0%, without a DLR: 64.1%) of RCTs were not successful, as characterized by the presence of an apical lesion. In particular, the failure rate was high for teeth with a DLR (85.0%), indicating the dif-ficulty performing RCT for such cases. Therefore, it is important to ensure that the lesions are diag-nosed accurately using CBCT and the procedure is performed with high technical competence using a microscope.

This study has possible meth-odologic limitations. Potential se-lection bias cannot be excluded, and the sample was relatively small. Therefore, further research is necessary to validate these re-sults.

Fig 2 Mandibular first molar with a distolingual root (red arrows) and an apical lesion (white arrows).


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CONCLUSIONS

The results of the present study showed that the incidence of a DLR in mandibular first perma-nent molars in a Japanese popu-lation on CBCT was 30.4%. The rate of RCT failure characterized by radiolucency at the apex was

71.2%; specifically, failure rates for MB, ML, D or DB, and DLR alone were 47.5%, 50.9%, 50.9%, and 70.0%, respectively.

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest.

ETHICAL APPROVAL

This study was approved in the Re-search Ethics Review Board, with approval number ECN-R-373 (The Nippon Dental University School of Life Dentistry at Niigata).

TABLE 1 Incidence of a distolingual root (DLR) in permanent mandibular first molars on cone-beam computed tomography.

With a DLR Without a DLR Total

Male 18 (30.5%) 41 (69.5%) 59

Female 34 (30.4%) 78 (69.6%) 112

Total 52 (30.4%) 119 (69.6%) 171

TABLE 2 Incidence of root canal treatment (RCT) and apical lesions in permanent mandibular first molars on cone-beam computed tomography.

Vital Pulp RCTRCT

with apical lesion

With DLR 32 (61.5%) 20 (38.5%) 17 (32.7%)

Without DLR 80 (67.2%) 39 (32.8%) 25 (21.0%)

Total 112 (65.5%) 59 (34.5%) 42 (24.6%)

TABLE 3 Failure rate of each root canal in permanent mandibular first molars on cone-beam computed tomography.

RCT with a DLR (n=20)

RCT without a DLR (n=39)

Total (n=59)

Failure of PMFM 17 (85.0%) 25 (64.1%) 42 (71.2%)

Failure of MB root canal 10 (50.0%) 18 (46.2%) 28 (47.5%)

Failure of ML root canal 10 (50.0%) 20 (51.3%) 30 (50.9%)

Failure of D (DB) root canal 12 (60.0%) 18 (46.2%) 30 (50.9%)

Failure of DL root canal 14 (70.0%) − −

Total 112 (65.5%) 59 (34.5%) 42 (24.6%)

PMFM: Permanent Mandibular First molars



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REFERENCES


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EVALUATION OF INCIDENCE OF DISTOLINGUAL ROOT AND