Mandibular First Molar Having an Unusual Mesial Root Canal Morphology with Contradictory Cone-Beam Computed Tomography Findings: A Case Report Jogikalmat Krithikadatta, MDS,* Jojo Kottoor, BDS, † Chellaswamy Savarimalai Karumaran, MDS,* and Gunaseelan Rajan, MDS* Abstract Introduction: The objective of this article is to highlight the importance of having a thorough knowledge about the root canal anatomy and the possibility of misleading findings in the cone-beam computed tomography (CBCT) images. Methods: This case report presents the endodontic management of a right mandibular first molar with 2 roots and 2 canals. A CBCT imaging was performed to ascertain this rare root canal anatomy. Results: The clinical and radiographic diagnosis of the existence of a single root canal within the mesial root of mandibular first molar did not correlate with the CBCT findings. Conclusions: The confirmative diag- nosis should be based on cognitive deduction of the clin- ical picture and intelligent interpretation of radiologic information. (J Endod 2010;36:1712–1716) Key Words CBCT, cone-beam computerized tomography, image artifact, mandibular first molar, root canal anatomy O ne of the most important aspects in contemporary endodontics is to possess a thor- ough knowledge of the internal and external root anatomy. This aspect, coupled with a correct diagnosis and appropriate cleaning and shaping of the root canal system, would improve the overall treatment outcome (1). Mandibular first molars are the first permanent posterior teeth to erupt and most often have caries that could necessitate endodontic treatment (2). However, many variations exist with regards to its root and root canal anatomy, thus necessitating critical evaluation of each individual case for variations (3). This case report describes the successful nonsurgical endodontic management of mandibular first molars with a single canal in the mesial root, a canal configuration rarely reported in the literature. It also describes the artifacts that were observed when cone-beam computed tomography (CBCT) images were used to aid in the diagnosis and treatment of this varied anatomy, which could lead to a misdiagnosis and procedural mishaps. Case Report A 63-year-old woman was referred with a chief complaint of tooth decay in her lower right back teeth for 2 months. History revealed intermittent pain in the same tooth during mastication. The patient’s medical history was noncontributory. Clinical exam- ination revealed a grossly decayed right mandibular first molar (tooth #30). Neither fistulae nor edema was observed in the soft tissues. There was no pain or tenderness to palpation; tooth mobility was within physiological limits, and the gingival attachment apparatus was normal. The tooth was tender to vertical percussion. Thermal and elec- tric pulp testing (Parkel Electronics Division, Farmingdale, NY) elicited a negative response. The preoperative radiograph showed widening of the periapical periodontal ligament space in relation to the mesial root apex. From the clinical and radiographic findings a diagnosis of pulpal necrosis with symptomatic chronic apical periodontitis with tooth #30 was made, and endodontic treatment was initiated. Preoperative radiographic evaluation of the involved tooth did not indicate any variation in the root/root canal anatomy (Fig. 1A). The distal surface of the tooth was restored with composite resin (Z100; 3M Dental Products, St Paul, MN) after caries excavation to enable better isolation. The tooth was anesthetized by using 1.8 mL (30 mg) of 2% lidocaine containing 1:200,000 epinephrine (Xylocaine; AstraZeneca Pharma Ind Ltd, Bangalore, India). A rubber dam was placed, and a conventional endodontic access opening was established. The pulp chamber floor was shown to have only 2 canals connected by the developmental root fusion line (DRFL) (Fig. 1B). Coronal enlargement was done with a nickel-titanium (NiTi) ProTaper SX rotary file (Dentsply Maillefer, Ballaigues, Switzerland) to improve the straight-line access. Working length was determined with the help of an apex locator (Root ZX; Mor- ita, Tokyo, Japan) and later confirmed by using a radiograph. Multiple working length radiographs were taken at different angulations to identify the second mesial root canal. But the file in the mesial root canal remained centered, suggesting a single root canal (Fig. 1C). Cleaning and shaping were performed under rubber dam isolation by using ProTaper NiTi rotary instruments (Dentsply Maillefer), with a crown-down technique. Irrigation was performed by using normal saline, 2.5% sodium hypochlorite solution, and 17% ethylenediaminetetraacetic acid. The access and instrumentation up to this From the *Rajan Dental Institute, Mylapore, Chennai, Tamil Nadu, India; and † Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Maduravoyal, Chennai, Tamil Nadu, India. Address requests for reprints to Dr Jogikalmat Krithika- datta, Rajan Dental Institute No.56, Dr. R K Salai, Mylapore, Chennai, Tamil Nadu, India, 600004. E-mail address: drkrithikadatta@hotmail.com. 0099-2399/$0 - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.06.024 Case Report/Clinical Techniques 1712 Krithikadatta et al. JOE — Volume 36, Number 10, October 2010