Unusual root morphology in second mandibular molar with a radix entomolaris, and comparison between cone-beam computed tomography and digital periapical radiography: a case report
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Radix entomolaris presents with an unusual morphology and is a rare occurrence. It is mainly observed in mandibular first molars. The incidence varies in different populations but it is far from common. This is especially true for mandibular second molars which possess the lowest prevalence. Some case reports have shown the presence of this finding in mandibular second molars; however, cases of patients of a white background have not been reported.
The diagnosis and treatment of an infected radix entomolaris in a mandibular second molar in a 45-year-old white man is presented. The diagnosis was made with standard endodontic techniques. Conventional radiographic imaging was augmented with cone-beam computed tomography scans and three-dimensional images which were constructed with dedicated software. The endodontic treatment was done using accepted endodontic procedures. Clinical and radiographic evidence of healing was seen after a 14-month follow-up.
The implications of complex and unpredictable root anatomy are discussed in this report. The clinician should consider the possibility of encountering a mandibular second molar with a radix entomolaris. Cone-beam computed tomography is a useful tool in the diagnosis and improvement of root canal therapy.
KeywordsRoot Canal Endodontic Treatment Pulp Chamber Apical Periodontitis Mesial Root
Cone-beam computed tomography
The success of root canal treatment requires in-depth knowledge of the anatomy and of the internal and external morphology of the treated teeth. The clinician should anticipate and identify the normality as well as the anatomical alterations that may be present because therapeutic failure may result from failure to identify alterations, such as supplementary roots or canals .
Carabelli  described a supernumerary root that was located on the distolingual area of mandibular molars and called it “radix entomolaris” (RE), referring to it as “radix paramolaris” (RP) when located in the mesiobuccal (MB) area. The prevalence of this root is directly associated with ethnic groups and geographical areas. The RE is mainly observed in mandibular first molars with an incidence between 5.8 and 33.1% in Asian populations and populations with Mongoloid features (Inuit and American Indians) [3, 4, 5], in Indian populations between 2.19 and 13.3% [6, 7], in Arab populations between 2.3 and 6.0% [8, 9], in Euro-Asians between 1.0 and 4.2% [3, 10], in African populations between 0.7 and 3.1% [11, 12], and, finally, with whites of the European continent (Spain, Germany and UK) exhibiting a prevalence of 0%, 0.7% and 3.3% respectively [13, 14, 15], and with whites of the American continent (USA and Brazil) exhibiting a prevalence of 2.2% and 4.2%, respectively [16, 17].
The most common radicular morphology of the mandibular second molar in the white population is two roots and three canals (two mesial canals and one distal). The most frequent anatomical alteration is a single root with one single oval canal . It is the tooth with the lowest prevalence of RE, with percentages that vary from 0 to 1.3% [19, 20]. To date, cases of white patients with RE in mandibular second molar have not been reported.
This case report of a white patient presents endodontic treatment of a mandibular second molar with RE centrally located between the distal and mesial root components (TypeAC location, according to Carlsen and Alexandersen ), type III curvature, according to De Moor et al.  (curvature in the coronal third and buccal curvature from the middle third or apical third of the root) and type III radiographic, according to Wang et al.  (full overlapping from the coronal third to apical third), as well as the presence of four independent canals in which the diagnostic accuracy of cone-beam computed tomography (CBCT) and digital periapical radiography (PR) are compared.
Radix entomolaris in a mandibular second molar. Three-dimensional rendered images. Postoperative follow-up. (MP4 1887 kb)
Depending on the ethnic origin, RE in mandibular first molar may be a common anatomical alteration, as is the case with Asian patients , or an atypical morphology, as in white patients . For the mandibular second molar, studies indicate that RE is a dysmorphic alteration (rare or unusual morphological alteration) even in ethnic populations with high rates of RE in mandibular first molars , and a third root in these teeth is linked more to the RP .
Alterations in the number of canals have been observed, such as those found by Pineda and Kuttler  in an “in vivo” study with patients of Mexican origin, revealing that 3% of mandibular second molars had four independent canals. Vertucci  reported, in an “in vitro” study, a 5% prevalence of these teeth with four canals in American populations of white ethnicity and, similarly, Walker  encountered a prevalence of 1% in the population of the south of China. Furthermore, cases with five (three in the mesial root and two in the distal root) and seven root canal systems (four in the mesial root and three in the distal root) have been reported [28, 29]. Although these anatomical aberrations are important alterations, most of these findings have been reported in mandibular second molars with only two roots. Alterations in number of roots have been observed in an “in vivo” study  with patients from China, revealing that 1.3% of mandibular second molars had three roots. Two cases with patients of Indian origin [30, 31] reported similar features (three roots, RE). Furthermore, a case (extracted mandibular second molar) with four roots in a patient from Sri Lanka  was reported. However, only one case with a patient of white origin with three roots (RP) has been reported . Therefore, this is the first report of such a case (RE) in this population.
The majority of the orthoradial orientation of the PRs and the ability to distinguish individual REs became increasingly difficult because of the overlapping of the adjacent distobuccal root; for this, a 25-degree mesioradial orientation would be a better option in mandibular first molars . Nonetheless, endodontic therapy in mandibular second molars is a more complicated issue than first molars due to the posterior position and consequent problems when taking proper PRs, eventually leading to gag reflex in the patient. For the case presented here, we faced these difficulties, and it was not possible to perform the initial PR with a mesioradial orientation.
The use of the CBCT on mandibular second molars is an excellent option to detect the anatomy and to mitigate the abovementioned inconveniences; the axial and coronal views and three-dimensional rendered images are a good option for a correct diagnosis and to observe the characteristics of the RE. CBCT, together with dental imaging software, allows us to measure the angles and distances with real values; thus, the spatial location of a structure, such as the entrance of the RE orifice in the pulp chamber, may be uncovered. It is important to align the long axis of the imaging plane with a specific anatomic structure for the values to be exact: taking the closest mesial root canal orifice to the radix as reference, helps to determine whether it is an entomolaris (ML) or a paramolaris (MB), thus forming an acute angle not greater than 90 degrees together with the distal root canal orifice and the radix for improved clinical interpretation (Fig. 1e). Today, precise instruments that transfer the information from the CBCT to a clinical setting are not available. However, the operating microscope offers increased visualization and light to use this information with approximately exact details (Fig. 1f, g).
Another aspect that should be highlighted is the short-, mid- and long-term postoperative controls that should be performed after endodontic treatment. The majority of the case reports indicate high-quality postoperative results but follow-ups performed using only PRs [22, 24]. A correct root canal treatment seen on the PR is not an absolute indicator of endodontic success. If we only consider the technique on its own, PRs offer inaccurate information on the situation compared with CBCT  because they provide a bi-dimensional image on the tri-dimensional structure of the teeth. As the canals are largely oval with the longer axis in the buccolingual or buccopalatal direction and the shorter axis in the mesiodistal direction, canal obturation can be difficult because PRs reveal only the shorter axis. In addition, PRs are more likely to miss apical periodontitis when it is still present . This assumption is supported in this case, where postoperative PR control (14 months) revealed complete bone remineralization of the periapical lesion of the distal root (Fig. 3a), whereas a coronal section of the CBCT revealed partial remineralization of the lesion (Fig. 3b). Furthermore, the postoperative and control PRs revealed complete sealing of the four canals, whereas on an axial section of the CBCT (section 1mm from the radiographic apex), the RE is not sealed in the last millimeter of the canal (Fig. 3d). Finally, the three-dimensional rendered image (Fig. 3e) indicates a radiopaque change on the final millimeters of the MB and RE canals with low homogeneity of the gutta-percha in the area, which could be a consequence of the complex system of the radicular canals. Whilst this highlights the details observed with the CBCT in comparison to the periapical radiographic images, these findings did not affect the healing process.
The implications of complex and unpredictable root anatomy are discussed in this report. The clinician should consider the possibility of encountering a mandibular second molar with three roots (RE). CBCT together with the operating microscope and ultrasonic tips are useful tools in the diagnosis and improvement of root canal therapy, providing greater security, predictability and overall efficiency when considering the technique, the biology and the clinical time needed.
Written informed consent was obtained from the patient for publication of this Case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
We are grateful to Marisol Calviño and Beatriz López for their varied contributions and support in this case report.
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