Diagnosis, Evaluation, and Endodontic Management of Rare Four-Rooted Mandibular Second Molar Using CBCT

Additionally, understanding the anatomy of the root is crucial. This includes the number of roots, the number of canals in each root, the lengths of roots and their orientation, the most prevalent curvatures, and the outline form of each root in all dimensions. Ordinarily, traditional diagnostic methods such as conventional radiography produce 2-dimensional (2D) images of an object with accuracy that may be incomplete due to anatomical noise. Conversely, cone-beam computed tomography (CBCT) produces 3-dimensional (3D) images with increased geometrical accuracy and image measurements in any plane without distortion. The use of CBCT helps in assessing tooth morphology and root canal curvature and configuration, which aids the clinician in modifying the access cavity preparation for cleaning and shaping. It helps clinicians avoid mistakes and has improved the outcomes of endodontic treatment.⁴

Typically, the number of mandibular second molar roots ranges from one to three.⁵ However, the incidence of four-rooted mandibular second molars is possible, although it is less than 1%.⁶ Thus, the four-rooted mandibular second molar observed in the present case seems to be a rare developmental anomaly of the molar root form.

Cases of the following anatomical configurations have been reported: mandibular second molar with three separate independent mesial roots and one distal root; mandibular second molar with two mesial and two distal independent roots; and mandibular second molar with two mesial and one distal root with radix entomolaris.^7-10 Although numerous studies have been undertaken, statistical data for various populations regarding incidence of four-rooted mandibular molars still has not been presented, except for 0.55% in the Israeli population.^11-19

In the present case report a rare morphologic variation of a mandibular second molar with four roots and four canals is evaluated with the use of CBCT. Orifice location to gain access is assessed through the observation of developmental root fusion lines on the pulpal floor. The successful nonsurgical endodontic treatment is described.

An 18-year-old female patient reported with a chief complaint of a discolored tooth with sensitivity to hot and cold in the lower left posterior region of her jaw for the previous 15 to 20 days. Her medical and family history was noncontributory. Upon clinical examination, deep caries in relation to the left mandibular second molar was observed. Sensibility tests performed with an electric pulp tester (Digitest^® II, Parkell, parkell.com) elicited a premature response, and cold testing with cold spray (Roeko Endo-Frost, Coltene, coltene.com) caused an intense lingering pain. Mild tenderness on percussion was present.

Upon radiographic examination, occlusal radiolucency approximating pulp was noticed (Figure 1). The radiographic apical contour of the left mandibular second molar with presence of a double periodontal ligament outline of the roots revealed the existence of supernumerary roots. To confirm the 2D findings of the radiograph, it was recommended that CBCT imaging be taken, and the patient provided consent to do so.

Axial, coronal, and sagittal CBCT images (CS 9300, Carestream Dental, carestreamdental.com) (internal version 3.5.15.0 software at 5 cm x 5 cm, 85 kV, 8 mA, 20 s, 985 mGy·cm²) ranging from the pulp chamber to the apex were examined to assess the associated variations related to number of roots, number of root canals, and canal configurations. Type I root canal²⁰ was present in each of four roots (Figure 2 and Figure 3). From the clinical and radiographic findings, a diagnosis of symptomatic irreversible pulpitis with symptomatic apical periodontitis was made, and nonsurgical endodontic treatment was advised.

At the first visit, the tooth was anesthetized with local anesthesia 2% lignocaine with 1:200,000 adrenaline (Xylocaine^®, AstraZeneca Pharma India Ltd., astrazeneca.com), followed by rubber dam isolation (Hygenic^® Dental Dam Kit, Coltene). Pulpal anesthesia was confirmed by cold test.

An endodontic access cavity was prepared with an endodontic access bur (ESE-014 Endo Safe End, SS White, sswhitedental.com). The cavity was modified from a conventional triangular shape to trapezoidal in order to locate and access the orifice of additional roots. Visual inspection of the dentin map and exploration of the pulp chamber floor using an endodontic explorer (DG16 Endo Explorer, EXDF166, Hu-Friedy, hu-friedy.com) suggested two mesial and two distal canal orifices (Figure 4). Upon access, it was confirmed that each canal contained vital pulp tissue, as evidenced by the presence of blood in the pulp chamber.

Root canals were negotiated with a size 10 K-file (NiTiFlex, Dentsply Sirona, dentsplysirona.com), and working length was determined using an electronic apex locator (Root ZX mini, Morita, morita.com) and confirmed with a digital radiograph (Figure 5). Cleaning and shaping was done using a crown-down technique with nickel-titanium files (HyFlex^™ CM File System, Coltene). Irrigation was sequentially performed using 5.25% sodium hypochlorite, 17% ethylenediaminetetraacetic acid (EDTA) (EndoPrep Solution, Dentsply Sirona), and normal saline. Corresponding gutta-percha master cones (Dentsply Sirona) 30/4 for the mesiobuccal (MB), mesiolingual (ML), and distolingual (DL) canals and 25/4 for the distobuccal (DB) canal were selected and a radiograph was taken (Figure 6).

The canals were obturated by cold lateral compaction with root canal sealer (AH Plus^®, Dentsply Sirona). Resin-modified glass-ionomer cement (Ketac^™ Nano, 3M Oral Care, 3m.com) was applied to seal the orifice on the pulpal floor. Then, the access cavity was restored with composite resin (Tetric^® N-Ceram, Ivoclar Vivadent, ivoclarvivadent.com) (Figure 7).

Post-treatment follow-up confirmed that the preoperative symptoms had dissipated. A radiograph at 1-year follow-up is presented in Figure 8.

Root development starts during the bell stage of odontogenesis near the Hertwig epithelial root sheath (HERS). HERS is present between two mesenchymal structures, dental papilla and dental follicle, which play a major role in root formation. The apical appendage of a root sheath bends to form a collar-like structure that grows apically around the pulp. However, in multirooted teeth, extensions of multiple collars develop and grow from the periphery of the pulpal chamber toward the center of it until they meet each other. Thus, in four-rooted teeth, four collars form by invagination of epithelial cells during root formation.^20,21

Variations in the internal and external anatomy of teeth are present in different races and even individuals. Two-dimensional, radiographic evaluation is an important, fundamental tool for diagnosis and clinical assessment of the tooth. Unusual changes that occur in tooth structure may demand further evaluation with the use of 3D imaging. CBCT has improved diagnostic accuracy and therapeutic efficacy, enhancing the outcome of endodontic management of complex tooth structure.²² In the present case of a mandibular second molar with four roots and four canals, diagnosis and interpretation was based initially on conventional radiographs at mesial and distal angles. To confirm the findings and to better understand the variation and curvature in the root and root canal at the coronal, middle, and apical levels, CBCT imaging was performed.⁴

Researchers have suggested that mandibular second molars require a high degree of attention because the number of roots and canals vary considerably.⁶ In certain circumstances, if the clinician is unable to detect all of the roots and canals, the root canals may inadvertently be left untreated during endodontic therapy, and, consequently, endodontic failure could occur.^5,23

The number of roots in a mandibular second molar typically ranges from one to three.⁵ Incidence of the presence of a third root was 2.8% in a population of Mongolian origin, 1.8% for a Black population, and 1.7% in Caucasians.²⁴ In the mandibular second molar the most prevalent canal pattern in the mesial root is type III, followed by type IV and type II; the most prevalent canal pattern in the distal root is type I, with type II and type IV (Mongoloid trait) occurring rarely.^11,14 The prevalence of three-rooted mandibular second molars in an Indian population was 8.98% and 1.2% in a Thai population, while it was 0% in a Burmese population.¹² A high prevalence of c-shaped canals and a low prevalence of three roots were observed in the mandibular second molars of a Korean population.²⁵ In some population groups, such as Indian and Jordanian, two roots and three canals are more common, followed by c-shaped canals.^12,17Even incidence of four roots in first molars is 0.04% in a Japanese population, with several case reports documenting this.⁶

Table 1 is a tabulation of various studies representing data on morphological variation in mandibular second molar teeth in different populations.^{11-17,19,26-30} Table 2 lists various case reports of mandibular second molars with four roots.^7,8,10,31-33

The present case had two mesial and two distal roots with MB, ML, DB, and DL canal orifices, which is a highly uncommon occurrence.³⁴ In such a case, the developmental lines in the pulp chamber floor follow a clinical configuration like a letter "x." The angle formed in four-rooted mandibular molars between the developmental root fusion lines that join both the mesial and distal orifices is typically more acute. Kottoor et al described the "x" pattern of developmental fused lines and noted that it can be used as a diagnostic criterion for a four-rooted mandibular molar.³⁵ The present case report also confirms that hypothesis.

Successful endodontic treatment begins with proper clinical and radiographic examination. Clinicians should be acutely aware of the complexity of mandibular second molar disparities and the extreme variability of the morphology of these root canals. In the present case, diagnosis and endodontic management of a mandibular second molar with four roots were carried out based on thorough clinical and radiographic interpretation. CBCT is an essential tool for the evaluation of anatomical variation, although currently it is a complementary modality for specific applications rather than a replacement for 2D imaging. Practitioners must be vigilant in their endodontic treatment, as variations of root and canal anatomy may be encountered at any time during a procedure.

Tanvi Paliwal, BDS, Postgraduate Student, Department of Conservative Dentistry and Endodontics, K.D. Dental College and Hospital, Uttar Pradesh, India

Rhitu Shekhar, MDS, Associate Professor, Department of Conservative Dentistry and Endodontics, K.D. Dental College and Hospital, Uttar Pradesh, India

Manoj Kumar Hans, MDS, Professor and Head, Department of Conservative Dentistry and Endodontics, Geetanjali Dental and Research Institute, Udaipur, Rajasthan, India

Rohit Paul, MDS, Professor and Department Head, Department of Conservative Dentistry and Endodontics, K.D. Dental College and Hospital, Uttar Pradesh, India

Suresh Pandey, MDS, Private Practice, Lucknow, India