The Importance of Cone-Beam Computed Tomography in Endodontic Treatment of a Mandibular Premolar With Atypical Anatomy: A Case Report

Mandibular premolars are typically described as having a single root and a single, broad root canal in the buccolingual direction as opposed to the mesiodistal direction. Anatomical variations, however, can be found in this tooth's root canal system (RCS). Such variations may include the presence of two, three, or four canals, as well as a C-shaped configuration.¹

The C-shaped canal has a cross-section similar in appearance to the letter "C" and its main anatomical characteristic is the presence of one or more isthmuses, connecting individual canals. It is usually found in mandibular second molar teeth.² However, it can also manifest in the mandibular first molars and premolars as well as in maxillary molars and lateral incisors, but with a low prevalence.³ This morphological complexity creates challenges with regard to procedures for chemical-mechanical preparation and filling of the RCS, and this represents a considerable potential threat to the prognosis of endodontic treatment.⁴

Having a thorough knowledge of and being able to adequately detect the anatomy of the RCS and its variations in morphology before beginning endodontic treatment will increase the chances of a successful procedure.⁵ Cone-beam computed tomography (CBCT) has been widely used to investigate anatomical variations in greater detail in a 3-dimensional form, thus enabling better predictability of the treatment.⁶ The objective of the present case study, therefore, is to report the endodontic treatment of a mandibular premolar with a C-shaped configuration based on the use of CBCT as a valuable diagnostic aid and in treatment planning.

Case Report

A 14-year-old female patient was referred to the endodontic specialization clinic of the Dentistry College of Recife in Brazil for endodontic treatment of tooth No. 21. During the anamnesis, the patient reported having had a history of painful symptoms in this tooth. Clinical examination revealed negative responses to thermal testing in cold mode (Endo-Ice, Coltene, coltene.com), percussion, palpation, and mobility testing. Upon periapical radiographic examination, the presence of a radiolucent image, suggestive of a periapical lesion, was verified, and an atypical anatomy was associated with the tooth in question (Figure 1). A CBCT was then taken in order to obtain a more in-depth and accurate diagnosis; it demonstrated the presence of a C-shaped canal (Figure 2 through Figure 4). The resulting diagnosis showed asymptomatic apical periodontitis. The endodontic treatment would be performed in two sessions.

First Session

In the first session, after local anesthesia was administered (2% mepivacaine with 1:100,000 epinephrine), absolute isolation of the tooth was performed. Subsequently, decontamination of the rubber sheet was done with sterile gauze and 2.5% sodium hypochlorite. Refinement of the coronal access with a #1014 spherical diamond tip (KG Sorensen, kgsorensen.com.br), compatible with the diameter of the pulp chamber, was completed, and a pulp opening drill (Endo-Z drill, Dentsply Maillefer, maillefer.com) was used to finish the preparation.

Next, the chemical-mechanical preparation was performed, starting with a #10 hand file (Dentsply Maillefer) to conduct the root canal exploration, and later with a rotatory file system, 25.08, 30.05, and 35.05 (ProDesign S, Easy Dental Equipment, easy.odo.br), according to the manufacturer's instruction. The chemical solution was 2.5% sodium hypochlorite. Dentistry was measured electronically using an apex locator (Root ZX, J Morita Corp., morita.com). After apical preparation, 5 ml of a 17% EDTA (ethylenediamine tetraacetic acid) solution (Maquira, maquira.com.br) was used to remove the smear layer and agitated for 1 minute (3 x 20 seconds) with an agitation device (Easy Clean, Easy Dental Equipment). This was followed by application of 5 ml of 0.9% saline. Intracanal medication based on calcium hydroxide (UltraCal^® XS, Ultradent, ultradent.com) was used for 15 days.

Second Session and Follow-up

In the second session, the calcium hydroxide was removed using 2.5% sodium hypochlorite, 0.9% saline, and 17% EDTA. The filling was performed using the lateral condensation technique with cement based on zinc oxide and eugenol (Endofill, Dentsply Maillefer).⁷ Coronal sealing was performed with composite resin (Filtek^™ Z350, 3M Oral Care, 3m.com), and the patient was referred for final restoration (Figure 5).

Clinical and radiographic follow-up was carried out 6 months and 1 year after the endodontic treatment was completed (Figure 6 and Figure 7). At 1 year post-treatment, the absence of painful symptoms, edema, and fistula was verified, as was the reduction of the radiolucency that was suggestive of a periapical lesion.

Discussion

Some authors have stated that ethnicity may have an influence on the prevalence of a C-shaped root canal and that the methodologies involved in the analysis of the specimens also have an impact.^3,8,9 Some studies using CBCT reported the presence of C-shaped morphology in mandibular premolars ranging from 1.1% to 2.3%.^10,11 The most dominant type of configuration found was C2, according to the classification by Fan et al,¹² which presents the shape of the canal similar to a semicolon, resulting from the discontinuation of the "C" outline. However, in the present study, the configuration found was C1, that is, an uninterrupted canal without separation or division. The etiology of the C-shaped canal may be related to the failure of Hertwig's epithelial sheath fusing on the lingual or buccal surface of the root.¹³

Nonsurgical treatment of the root canal system of teeth with anatomical variations becomes more challenging due to difficulties associated with disinfection and debridement, which might result in the development and/or maintenance of periradicular pathologies.⁶ Complex irregularities at the apical level that may harbor tissue leftovers, infected debris, and/or biofilm are often reported in C-shaped root canals.¹⁴ Kim et al demonstrated that the most common cause of failure in endodontic treatment of C-shaped canals was the presence of a leaky canal and isthmus.³ Within this context, the introduction of means to strengthen the action of chemical substances is essential.¹⁵

Thus, in the present case, 2.5% sodium hypochlorite and 17% EDTA were used because of their effective antimicrobial and tissue dissolution properties (organic and inorganic) associated with the activation medium through the use of an "easy clean" device, which is a plastic device, 25.04, with a wing-shaped cross-section. Its basic principle is the mechanical agitation of the chemical substance, promoting cleaning of the canal walls through the removal of debris that had adhered to the internal walls of the RCS. This means of activation has a more accessible cost compared to ultrasonic inserts, among other methods, and provides similar advantages.¹⁶ Rodrigues et al and Sousa et al evaluated canal wall cleanliness after using passive ultrasonic irrigation (PUI) and easy clean agitation systems during endodontic retreatment of roots filled.^17,18 Both author groups observed that the agitation instrumentation was as effective as PUI for removal of the remaining filling material. In the present case, the use of intracanal calcium hydroxide medication was also required to increase the disinfection efficacy of the RCS.

According to Patel et al, the 3-dimensional radiographic evaluation of teeth and their adjacent structures based on the use of CBCT is desirable to assist in the diagnosis and/or treatment of anatomical complexities.¹⁹ The limitations of conventional radiography are well established, such as the restrictions of viewing a 3-dimensional structure in only two dimensions, the masking of areas of interest, and image distortions. These shortcomings are reflected in inaccurate diagnoses of morphological changes, thus restricting the choice of the treatment planning.²⁰ Consequently, the use of CBCT, as demonstrated in the present case, is essential, as the superior visualization of the internal and external anatomy and the perception of the configuration of the "C" canal in three dimensions increased the predictability of the treatment.

Conclusion

In-depth knowledge of the internal anatomy of the root canal system, along with its variations, is necessary for the favorable prognosis of endodontic treatment. In this regard, CBCT is an important tool to assist in determining the correct diagnosis and understanding the anatomical complexity to be treated. The variation of C-shaped canals is challenging due to difficulties encountered during the stages of chemical-mechanical preparation and filling. Therefore, means of enhancing disinfection are necessary.

Natália Gomes de Oliveira, DDS, MSc, PhD
PhD in Dentistry, Dentistry School, Universidade de Pernambuco (UPE), Recife, Pernambuco, Brazil

Pâmella Recco Álvares, DDS, MSc, PhD
PhD in Dentistry, Dentistry School, Universidade de Pernambuco (UPE), Recife, Pernambuco, Brazil

Casimiro Ricardo Oliveira Passos, DDS
Specialist in Endodontics, Brazilian Dental Association, Recife, Pernambuco, Brazil

Sandra Maria Alves Sayão Maia, DDS, MSc, PhD
Adjunct Professor, Dentistry School, Universidade de Pernambuco (UPE), Recife, Pernambuco, Brazil

Marianne de Vasconcelos Carvalho, DDS, MSc, PhD
Associate Professor, Dentistry School, Universidade de Pernambuco (UPE), Recife, Pernambuco, Brazil

Paulo Maurício Reis de Melo Júnior, DDS, MSc, PhD
Adjunct Professor, Dentistry School, Universidade de Pernambuco (UPE), Recife, Pernambuco, Brazil