Single C-shaped canal in mandibular first molar: A case report.

The variability of root canal system morphology presents a continuous challenge to endodontic diagnosis and therapeutics. There have been reports of teeth with multiple roots and canals as also those with lesser number of root and root canals. Variations of root canal systems need not always be in the form of extra canals. Clinicians should be aware that there is a possibility of existence of fewer numbers of roots and root canals than normal, which presents varied canal anatomy and poses a challenge to the clinician's expertise. This case report deals with the management of an unusual case of C-shaped canal in mandibular molar with two buccally fused roots. Cone-beam computed tomography (CBCT) was employed to confirm the extension of the unusual anatomy. The Self Adjusting File (SAF) system was used to ensure complete cleaning of the canal system. One-year follow-up of the case showed good healing. The clinician should expect to encounter unusual features when performing endodontic treatment. Use of diagnostic aids like CBCT, improved magnification with dental operating microscope, and the use of novel file systems like SAF ensure success.

INTRODUCTION

A thorough knowledge of root canal anatomy is necessary to achieve appropriate cleaning and shaping of the root canal system and ensure success of endodontic treatment.[1] Very often, the mandibular first molars require endodontic treatment as they are the first permanent posterior teeth to erupt and are commonly affected by caries.[2] The mandibular first molar presents with two well-defined roots: A mesial root with two canals and a distal root with one or two canals. Variations in the form, configuration, and number of root canals in mandibular molars have been discussed extensively in endodontic literature.[34] These include five,[5] six,[6] and seven root canals;[7] middle mesial canal;[8] middle distal canal;[9] four canals in mesial root;[10] four canals in distal root;[11] radix entomolaris[12] and paramolaris; and C-shaped canal.[13] These reports include cases with more number of canals than normal.

However, the clinician should be aware of the possibility of the existence of lesser number of roots or canals. Gopikrishna et al., published a case of single root with a single canal in a maxillary first molar.[14] Recently, Krithikadatta et al., have reported a case of a mandibular first molar with two roots and two root canals.[15]

The purpose of this paper is to report the management of the uncommon anatomy of a mandibular first molar with two fused roots and single C-shaped canal. This case report details the use of the Self Adjusting File (SAF) system which is particularly useful in cleaning of such C-shaped canals.

CASE REPORT

A 39-year-old female patient reported to the Department of Endodontics with the chief complaint of spontaneous pain in the lower left posterior region. History revealed intermittent pain with the left mandibular first molar for the past 2 months, which had increased in intensity for the past 3 days. Subjective symptoms included sensitivity to thermal stimuli and an increase in intensity of pain. The patient's medical history was noncontributory. Previous dental history included extraction of the mandibular left second molar 3-4 years ago due to caries. Clinical examination of the left mandibular first molar revealed the presence of a large distoocclusal carious lesion which was sensitive to percussion. Periodontal probing around the tooth showed normal alveolar bone morphology, normal sulcular depth, absence of pockets, and mobility within physiological limits. Sensibility testing with dry ice (RC Ice, Prime Dental Products Pvt Ltd, Mumbai, India) caused an intense lingering pain; whereas, electric pulp testing (Parkell Electronics Division, Farmingdale, NY) showed exaggerated response. Preoperative radiographs revealed a distoocclusal radiolucency approaching the pulp space with a widened periodontal ligament space adjacent to the root apex [Figure 1a]. Multiple angulated radiographs confirmed the presence of fused roots. From the sensibility tests and clinical and radiographic examination, a diagnosis of symptomatic irreversible pulpitis with symptomatic apical periodontitis was made and routine nonsurgical endodontic treatment was planned. Treatment plan was explained to the patient and consent obtained.

Figure 1

(a) Preoperative radiograph. (b) Clinical view of access cavity. (c) Coronal-apical views in CBCT. (d) Cleaning and shaping with SAF. CBCT = Cone-beam computed tomography, SAF = Self Adjusting File

Local anesthesia was induced using 1.8 ml 2% lidocaine with 1: 200,000 epinephrine (Xylocaine, AstraZeneca Pharma India Ltd, Bangalore, India). Following caries excavation, the distal surface of the tooth was restored with Intermediate Restorative Material (IRM; L. D. Caulk Co., Milford, DE, USA). Rubber dam was placed and a conventional endodontic access opening was established with an Endo Access Bur (Dentsply Tulsa, Tulsa, OK). On access opening, a single large C-shaped canal was located in the center of the pulp chamber [Figure 1b]. After clinical examination with dental operating microscope (Moller Wedel, Germany), it was found that the tooth had two root canals which were fused buccally and had single C-shaped canal. It was decided to confirm the extension of the C-shaped canal with a CBCT scan (Carestream CS9300, 85kV, 8mA, 19.96s). This confirmed the fusion of the two buccal roots, and a single C-shaped canal clearly visible in the coronal section which extended all the way till the apex [Figure 1c].

Working length was determined using an apex locator (Root ZX II, Morita, Tokyo, Japan) and confirmed with radiographs. Cleaning and shaping was done using circumferential filing technique with ISO 2% taper files up to size 25 (Mani Inc, Tochigi-Ken, Japan) and further cleaning and shaping done with SAF (ReDent Nova, Israel) of 2mm diameter and 21mm length with pecking motion having 0.4mm amplitude and 5,000 oscillations per minute [Figure 1d]. Irrigation was performed using normal saline (Nirma Pvt limited, Gujarat, India), 5.25% sodium hypochlorite solution (Vishal Dental Products, Mumbai, India), and 17% ethylene diamine tetra acetic acid (EDTA; Prime Dental Products Pvt Ltd, Mumbai, India) as final flush. Final rinsing of the canal was performed using normal saline. The canal was dried with absorbent points (Dentsply Maillefer, Ballaigues, Switzerland) and obturation was performed using sectional method for the apical third [Figure 2a], followed by backfill with thermoplasticized gutta-percha using Obtura II (Obtura Spartan, Wendt Street Algonquin, IL, US) and AH Plus resin sealer (Maillefer Dentsply, Konstanz, Germany) [Figure 2b]. After completion of root canal treatment, the access cavity was restored using resin composite (3M ESPE Dental Products, St Paul, MN), followed by full coverage crown. One-year follow-up showed good healing [Figure 2c].

Figure 2

(a) Sectional obturation, (b) Post-obturation radiograph. (c) One-year follow-up radiograph

DISCUSSION

The mandibular first molars erupt at an age of 6-7 years and apical closure is usually completed by 8-9 years. The completion of canal differentiation commences about 3-6 years after root completion.[15] Any disturbances in this differentiation can result in variations in canal anatomy. Sabala et al.,[16] has stated that the rarer the aberration is, the greater the probability of it being bilateral. In this case, the contralateral mandibular posterior was extracted, and hence, the morphology could not be determined. Fava et al.,[17] had identified the existence of such anatomical variations in second molars in all the maxillary and mandibular second molars. Majority of the permanent mandibular first molars typically present with two well-defined roots, a mesial root with two canals and a distal root with a wide oval canal or two round canals.[3] Apart from these presentations, wide variations of root and canal configuration of the mandibular first molars have been reported in the literature.[513]

Systematic review of literature on canal morphology of the mandibular first molar by De Pablo et al.,[18] and Ballulaya et al.,[19] has not found cases of single root and single canal. This morphological variation has been documented in an in vitro study done by Reuben et al.[20] Out of 125 samples of mandibular first molars from an Indian population, only one sample had a single root and single canal (0.85%). Further, C-shaped canal was found in only one sample. Demirbuga et al.,[21] evaluated the root and canal morphology of mandibular first and second molars in Turkish population and reported an incidence of 0.12% for single root and canal and 0.85% for C-shaped canals in mandibular first molars. Sooriaprakas et al., have reported the incidence of a single root and single canal in mandibular first molar.[22] Table 1 illustrates variations in mandibular first molars according to different authors.

Table 1

Variations in mandibular molars

Radiographic examination is an essential component in endodontic treatment. The use of multiple preoperative radiographs or an additional radiographic view from a 20-degree mesial or distal projection increases the chances of detecting unusual root canal morphology.[23]

Kottoor et al.,[2425] and La et al.,[26] have suggested the use of CBCT for the purpose of determining the root canal morphology in cases with aberrations. In this particular case CBCT was advised to determine the root canal morphology and also extension of C-shaped canal towards the apex. CBCT interpretation clearly showed that this tooth had a single C-shaped canal which was beginning from the pulp chamber to apex without any furcation.

Melton et al.,[27] in 1991 had proposed a classification of C-shaped canals based on their cross-sectional shape. Fan et al.,[2829] in 2004 modified Melton's classification into the following categories:

Category I (C1): The shape was an interrupted “C” with no separation or division.

Category II (C2): The canal shape resembled a semicolon resulting from a discontinuation of the ‘C’ outline.

Category III (C3): Two or three separate canals (highest incidence).

Category IV (C4): Only one round or oval canal in that cross-section.

Category V (C5): No canal lumen could be observed (which is usually seen near the apex only).

In this case, the root canal would fall into category C1. The anatomic feature of such a canal is the presence of a fin or web which connects the individual canals. There is a large amount of debris seen in instrumented C-shaped canals which could lead to endodontic failure.[27] Use of hand or rotary endodontic files alone would not result in proper cleaning of such canal systems. The SAF system has a hollow core with interlocking lattice design. Since the file accommodates itself according to the shape of the canal, it is ideally suited for large, oval, or C-shaped canals. The constant irrigant flow is an added advantage. In this case, the enlargement was done initially using ISO taper files and finished with the SAF. Thermoplasticized obturation technique was chosen here due to the oval C-shaped canal outline. In combination with vertical compaction, this technique enables complete filling of the canal anatomy.

CONCLUSION

This case report presents the uncommon anatomy of mandibular first molar with two fused roots and single C-shaped canal. Careful inspection of the tooth under dental operating microscope and the correct choice of cleaning and shaping technique suitable for this uncommon root canal anatomy helps achieve success in such aberrant cases.