CBCT diagnosis and endodontic management of a maxillary first molar with unusual anatomy of two palatal canals: A case report.

It is crucial for any clinician to have a thorough knowledge about the normal anatomy of tooth and always be vigilant for any variations to ensure endodontic success. An anatomic variant like additional canals in the palatal root of maxillary molar is not commonly reported. This clinical case report presents the application of cone beam computed tomography as a useful imaging technique in endodontics for the management of teeth with aberrant anatomy. Here, maxillary first molar having two canals in the palatal root, two canals in mesiobuccal root and one canal in distobuccal root was managed successfully using cone beam computed tomography scan as a diagnostic aid.

INTRODUCTION

Thorough knowledge regarding the normal and abnormal root canal anatomy is highly critical for the success of endodontic therapy. It is imperative to identify the exact root canal architecture prior to initiating root canal treatment so as to accomplish thorough disinfection, debridement, shaping, and obturation of the entire root canal system. Inability to locate complexities or variations in root canal morphology can result in harboring of microorganisms and a resultant failure of endodontic treatment.

Maxillary molars are teeth known to present with great variations in root and root canal morphology. The greatest variation observed in maxillary first and second molars is with respect to their mesiobuccal roots.[123] Owing to the frequent existence of two canals in mesiobuccal roots, most frequent variation encountered in these teeth is three roots with four canals. Cleghorn et al. in their extensive review of literature on root and root canal systems of maxillary first molar observed that over 95% of maxillary first molars had three roots with 56.8% incidence of two canals and 43.1% incidence of one canal in mesiobuccal root.[3]

In contrast to mesiobuccal root, distobuccal and palatal roots of maxillary first molars show extremely low variations. The predominant anatomical form found in palatal root is a single root with single canal having a reported incidence of almost 99%.[3] Some authors have, however, reported seeing variations like two palatal roots with individual canals, single palatal root with two independent canals, and single palatal root with two canals joining in the apical third before exiting.[456] Baratto-Filho et al. reported the frequency of finding extra canal in mesiobuccal root (MB2) of maxillary first molars to be 92.85% (ex vivo results), 95.63% (clinical results) and 95.45% (cone beam computed tomography — CBCT results). Comparatively, the figures for the palatal root were only 2.05% (ex vivo results), 0.62% (clinical results), and 4.55% (CBCT results).[1] It was also noted that the ability to find additional canal was improved when CBCT was used for investigation.

The role of CBCT over conventional digital and film radiography in accurately determining the root morphology and canal configuration is well-established.[78] While performing endodontic treatment, radiographs are an integral part of treatment for identifying the number, pattern and curvature of root canals but offer limited information as they are two-dimensional representations of three-dimensional structures. Moreover, their interpretation can be confounded by the presence of unwanted shadows, geometric distortions, and superimpositions. CBCT overcomes these limitations by providing precise three-dimensional images with increased resolution. CBCT as an aid can greatly enhance detection and mapping of root canal systems with the potential to improve quality of root canal treatment.[2]

Despite the rare occurrence of additional canals in palatal root of maxillary molars, their existence should always be suspected and established to ensure success. This may necessitate employing CBCT if the clinician is unable to confirm the variation using radiographs. The clinical case presented here describes the management of a permanent maxillary first molar with two distinct palatal canals, two mesiobuccal canals, and one distobuccal canal using CBCT as a diagnostic aid.

CASE REPORT

A 35-year-old man presented with the chief complaint of pain in the upper right maxillary posterior region for past few days. The patient's medical history was non contributory. On clinical examination, maxillary right first molar had a deep carious lesion and responded positively to palpation and percussion. Electric pulp testing was indicative of irreversible pulp damage. Preoperative radiograph of tooth #16 revealed periapical radiolucency in association with its palatal root [Figure 1a]. Root canal treatment was proposed for the tooth and the patient consented to it.

Figure 1

(a) Pre-operative radiograph of tooth #16, (b) Occlusal view of the endodontic access showing the opening orifices of the mesiobuccal (MB1 and MB2), distobuccal (DB), and palatal (MP and DP) canals. (c) Postobturation radiograph (d) Radiograph at one year showing resolution of periapical radiolucency

Local anesthesia of 2% lignocaine with 1:100,000 epinephrine was administered prior to application of rubber dam. Under complete isolation, access cavity was prepared using Endo Access Kit (Dentsply, Switzerland). Removal of chamber roof dictated a trapezoidal form to the access cavity rather than triangular. Internal investigation revealed presence of three main root canal openings: Mesiobuccal (MB), distobuccal (DB), and Palatal (P). The palatal canal orifice appeared to be much constricted than routinely found. On the radiograph, clear demarcation of the palatal canal was also not possible leading us to suspect some variation in the palatal root anatomy. Inspection of the chamber floor for determining the presence of any additional canals was repeated using DG 16 endodontic explorer under 2.5× magnification using dental loupes (Daray, Derbyshire). Intensive exploration revealed a catch at two points on the chamber floor. One stick of the explorer point was found almost midway at a line joining the mesiobuccal and palatal orifices and aroused slight pain and hemorrhage, characterizing it to be a second mesiobuccal canal orifice. The other catch point was located distal to the palatal opening already found but unlike the previous catch did not arouse any pain or hemorrhage.

The radiographs of the concerned tooth did not offer any conclusive information. To confirm whether the orifices located were additional canals in mesiobuccal and palatal roots and to determine the exact morphology of the variations, it was decided to perform CBCT of tooth #16.

A sterile cotton pellet was placed inside the pulp chamber, and the access cavity sealed with IRM (Caulk, Dentsply, USA). A CBCT scan (Next Generation i-CAT, Imaging Sciences International, Hatfield, PA, USA) of the maxillofacial region was undertaken with exposure parameters of 120 kV and 5.0 mA. An ultra-low radiation dose scan was done using a focused field of view. The images were reconstructed at 0.2 mm thickness increments. CBCT axial images of tooth 16 confirmed the presence of five canals: Two mesiobuccal (MB1 and MB2) canals, one distobuccal canal, and two palatal canals [Figure 2]. Both mesiobuccal and palatal canals seemed to follow the Vertucci type II canal pattern.[9]

Figure 2

Cone beam computed tomography (CBCT) axial slices of teeth 16 and 26 at (a) coronal, (b) middle, and (c) apical levels indicating presence of additional mesiobuccal and palatal canals

On subsequent visit of the patient, additional canals were located and instrumented. Initial instrumentation was performed using K flex #10 file. The working length of each canal was determined using electronic apex locator (Root ZX, J Morita Mfg. Corp., Japan) and confirmed radiographically. Coronal flaring was carried out using Gates-Glidden burs (numbers 3 and 2; Dentsply, Maillefer, Switzerland), and the root canals cleaned and shaped using crown down technique with sizes 15-40 Ni-Ti K files (Dentsply, Maillefer, Switzerland) [Figure 1b] using 17% EDTA. Copious irrigation of the canals was also done with 2.5% NaOCl. The Vertucci type II pattern was confirmed in both mesiobuccal and palatal roots. After the canals were properly dried with paper points, calcium hydroxide (Metapex, Meta Biomed Co. Ltd., Korea) was placed inside the canals and access cavity provisionally sealed with IRM (Caulk, Dentsply, USA). The patient was recalled after one week.

At one week, the patient was completely asymptomatic. The canals were obturated with gutta-percha (Dentsply, Maillefer, Switzerland) using cold lateral compaction technique and AH Plus resin as a sealer (Dentsply, De Trey, Germany) [Figure 1c]. The access cavity was permanently restored with resin composite. The patient was recalled after 1 year for follow up. At recall appointment, patient continued to be asymptomatic and radiograph showed periapical healing [Figure 1d].

DISCUSSION

This case report highlights the importance of accurately determining root canal morphology to improve endodontic treatment outcomes. Neglecting to locate extra canals can lead to incomplete elimination of microorganisms and is regarded as one of the major causes of endodontic failures. In the current case, two canals each were noted in the mesiobuccal and palatal roots of maxillary first molar.

Additional canal especially in the mesiobuccal root is a frequent finding in the permanent maxillary molars. In a CBCT study conducted in the Indian population, the most common canal morphology in the mesiobuccal roots of three-rooted first and second molars was seen to be type I (51.8% and 62%, respectively), followed by type IV (38.6% and 50%, respectively) canal system.[7] Authors have reported finding similarly high incidence of additional canals in the mesiobuccal root of maxillary molars in other populations as well.[21011] It is therefore recommended to customarily explore for the existence of an additional mesiobuccal canal when performing endodontic treatment in a maxillary first molar. On the other hand, distobuccal and palatal roots are known to have predominantly a single canal system. Anatomic variations involving the number of roots/root canals with respect to distobuccal and palatal roots are highly unusual and rare (less than 1%), nevertheless their existence cannot be ignored and should be thoroughly investigated.[3]

Presence of additional root canals can be confirmed using preoperative radiographs along with careful visualization and probing of the pulp chamber floor. Indistinct X-ray images, modified coronal access, and unusual location/size of canal openings are a few simple indicators of likely aberrant anatomy. In the current case, both conventional and digital radiographs were unable to provide definitive information on the anatomical variations. The outline of the palatal canal could not be delineated clearly on the radiographs but surely indicated presence of some aberrant anatomy in relation to the palatal root. Further, existence of extra canals was also suspected on clinical investigation. CBCT of tooth #16 was therefore performed to ascertain the exact root and canal morphology.

The higher accuracy of CBCT has greatly facilitated three-dimensional imaging and visualization of unusual anatomy and/or additional root canals that can often be missed on routine radiographs.[12131415] CBCT compared to conventional CT scans is an advancement in CT imaging that provides relatively high-spatial resolution of anatomic structures with much reduced patient radiation dose.[1617] Additionally, CBCT scanners use simpler, less complicated, and therefore, less expensive hardware (X-ray source and detector) making it quite popular as an office diagnostic tool.[18] Case reports in literature that have reported using CBCT for diagnosis of additional palatal canals in maxillary first molar are summarized in Table 1.[6192021]

Table 1

Case reports that have reported using cone beam computed tomography (CBCT) for diagnosis of additional canals in palatal root of maxillary first molar

CBCT of tooth #16 performed in this case confirmed the existence of two canals each in palatal and mesiobuccal roots. It greatly helped in diagnosis and improving treatment success by enabling description of the anatomic variations and the course of root canals precisely. Another interesting feature noted in CBCT was the presence of similar internal anatomy, i.e., one distobuccal canal, two mesiobuccal canals, and two palatal canals with Vertucci type II canal pattern in the contra lateral maxillary first molar [Figure 2]. Sabala et al. have reported that bilateral symmetry is a feature of aberrant anatomy; rarer the aberration, more common is the bilateral symmetry.[22] The anatomic variation should be highlighted on the patient's records so that if at all in future some treatment is required on the opposite side, the clinician is well-prepared.

Additionally, during the clinical procedure, roof of the pulp chamber guided a form of access cavity that was more trapezoidal. Careful exploration of the chamber floor with an endodontic explorer led to the identification of two catch points. Palatal canal opening when located was also unusually small in size. All these features when noted led to the suspicion that additional canals might be present. The experience of the clinician along with meticulous examination of the pulpal floor under magnification for detecting any variations is emphasized through this report.

CONCLUSION

The possibility of morphologic variations in a tooth should never be overlooked. Additional canals should be identified by all possible means as it enables the clinician to perform biomechanical preparation and sealing of the entire root canal system, thereby minimizing endodontic failure. In addition to a properly designed access cavity, angulated radiographs and routine use of loupes is suggested as it greatly increases visualization and the likelihood of locating additional canals. The clinician should consider using CBCT as an auxiliary tool for confirming the presence of complicated root canal anatomy when conventional radiographs are not very conclusive. Use of CBCT in endodontics is encouraged but should be limited to the assessment and treatment of only complex endodontic conditions such as identification of root canal system anomalies and determination of root curvature.