Cone-beam computed tomography diagnosis and nonsurgical endodontic management of a taurodontic mandibular first premolar with two roots and four canals: A rare case report.

Successful root canal treatment requires a thorough understanding of the normal root canal anatomy and possible variations for each tooth. Variations in the root canal anatomy are frequently associated with complex orientations of pulp tissues and complicating mechanical and chemical debridement. Inability to manage such complications may result in endodontic failure. Mandibular first premolars often exhibit a wide range of anatomic variations, complicating clinicians' treatment. This clinical case report discusses the cone-beam computed tomography (CBCT) diagnosis and nonsurgical management of a taurodontic mandibular first premolar with two roots and four canals under a dental operating microscope (DOM). In endodontically challenging cases, using a DOM and CBCT imaging can help the clinician gain a better understanding of the complex root canal anatomy, allowing the clinician to more efficiently explore, clean, shape, and obturate the root canal system. Copyright:

INTRODUCTION

Apical periodontitis can be successfully treated with root canal treatment, which involves appropriately cleaning and shaping the root canal system, followed by three-dimensional obturation with an inert filling material and a high-quality coronal restoration.[1] The root canal system is highly variable and can differ from tooth to tooth. Extra roots and canals, ramifications, apical deltas, isthmus, lateral canals, C-shaped canals, curved canals, calcified canals, and developmental anomalies such as Dens in dente, Dens evaginatus, palatogingival groove, taurodontism, and others may complicate the treatment.[2]

Taurodontism is a developmental anomaly of the tooth that lacks constriction at the level of the cementoenamel junction (CEJ) and is characterized by vertically elongated pulp chambers, apical displacement of the pulpal floor, and bifurcation or trifurcation of the roots in the middle or apical thirds of the root.[3] The overall incidence of taurodontism has been reported to range from 2.5% to 11.4%, with the mandibular molars being the most commonly affected, and there is no gender preference.[4] The presence of taurodontism in the mandibular first premolar is considered a rare anomaly, and previous studies reported that the prevalence of taurodontism in mandibular first premolars ranged from 0.42% to 5%.[56]

The majority of mandibular first premolars reportedly have a single root, with only a mere 1.8% having two roots. In addition, the majority (about 97.90%) of the mandibular first premolars bear only one root canal, while cases with three canals are as rare as 0.2%, and the rarest cases display four canals (<0.1%).[7] A good understanding of the internal and external anatomies and the proper use of modern equipment such as cone-beam computed tomography (CBCT) and the dental operating microscope (DOM) are essential for predictable root canal treatment of such teeth.

The purpose of this case report is to discuss the nonsurgical treatment of a left mandibular first premolar with a unique combination of taurodontism, two roots, and four root canals using CBCT and a DOM.

CASE REPORT

A 35-year-old Chinese male patient with a noncontributory medical history reported to Specialty Dental Clinic, MAHSA University, Selangor, Malaysia, with a chief complaint of pain and food lodgment with respect to (wrt) tooth #34 (mandibular left first premolar) for 1 month. The pain was mild in intensity, intermittent, aggravated on chewing food, and relieved upon taking medication. The patient's dental history was insignificant.

On clinical examination, oral hygiene was acceptable, and deep distal proximal caries was seen #34. The tooth was tender to percussion, and there was no evidence of swelling or an associated sinus tract. Periodontal pocket depths were within the normal limits. The electric pulp test (Digitest®, Parkell, New York, USA) showed a delayed response, whereas the cold test with Endofrost (Coltene Whaledent, Switzerland) gave a lingering reaction. On radiographic examination [Figure 1], tooth #34 showed distal proximal caries approaching the pulp chamber. In addition, the pulp chamber was elongated and bifurcated, resulting in two distinct roots (mesial and distal roots) in the middle third of the root. The periodontal ligament space was slightly enlarged, and a loss of continuity of the lamina dura was noted, without any associated periapical lesion with two roots.

Figure 1

Preoperative radiograph wrt #21

Based on clinical and radiographic examination, the diagnosis of symptomatic irreversible pulpitis with symptomatic apical periodontitis was made with tooth #34. The patient was scheduled for root canal treatment the following day. Before treatment, a CBCT scan was taken to confirm the number of root canals, as the tooth had a discrepancy in the anatomy on a radiograph. The patient gave consent, and three-dimensional, high-resolution images were taken. The anatomy of the tooth was recorded and analyzed in the axial and sagittal sections. The radiographic findings were confirmed by CBCT images of tooth #34, which revealed an elongated pulp chamber with two roots (mesial and distal) in sagittal sections [Figure 2]. In addition, the axial sections of CBCT images revealed the presence of two canals in each root (mesiobuccal, mesiolingual, distobuccal, and distolingual canals) [Figure 3]. The root canal treatment was initiated by obtaining consent from the patient.

Figure 2

Sagittal section of cone-beam computed tomography showing two roots (mesial and distal)

Figure 3

Axial section of cone-beam computed tomography showing four canals (mesiobuccal, mesiolingual, distobuccal, and distolingual)

The tooth was anesthetized, and rubber dam isolation was done. The caries was removed using a large round bur (Komet Dental, Brasseler, Germany), and the pulp chamber was accessed using a long shank round bur (Dentsply Maillefer, Ballaigues, Switzerland), under a DOM (Carl Zeiss, Oberkochen, Germany). Four root canal orifices were identified and located in the middle third of the root. Three orifices were situated at the same level, while the distobuccal orifice was at an angle to the floor of the pulp chamber. The access cavity was refined using ultrasonics with an Ultrawave ET18D tip (SATELEC, Merignac, France), and the orifice opener was used to achieve straight-line access to the root canals. The preendodontic buildup was done with composite resin (Dentsply Maillefer, Ballaigues, Switzerland) [Figure 4].

Figure 4

Four orifices are seen under the dental operating microscope

The canals were scouted and negotiated, and length determination was done using the electronic apex locator (ProPex® II, Dentsply Sirona Endodontics), a size #10 K-file (M-access, Dentsply Maillefer, Ballaigues, Switzerland), and RC-Prep (Premier® Dental, Plymouth Meeting, Pennsylvania), as lubrication. Since tooth #34 had four canals, it was not easy to place four K-files simultaneously to confirm the working length using a radiograph. Therefore, the radiograph was taken separately for the mesial and distal roots to confirm the working length [Figures 5 and 6]. The glide path was prepared using manual ISO standardized stainless steel K-files. Initially, a size #10 K-file (M-access, Dentsply Maillefer, Ballaigues, Switzerland) was used in a watch winding motion and later, subsequently increasing to size #15 K-file (M-access, Dentsply Maillefer, Ballaigues, Switzerland). The glide path was prepared until the size #15 K-file fit without tightness in all four root canals. The root canals were cleaned and shaped to the working length with more flexible and highly fracture-resistant rotary files up to 25.4% (HyFlex® CM, Coltene Whaledent, Switzerland). An intraoral periapical radiograph was taken to confirm the fit of the corresponding master gutta-percha cone (Coltene Whaledent, Switzerland) for the mesial and distal roots [Figures 7 and 8]. The root canals were thoroughly irrigated with 3% sodium hypochlorite throughout the cleaning and shaping procedure. Irrigation was performed with a flexible polypropylene plastic side-vented irrigating needle (IrriFlex®, PD, Switzerland). After cleaning and shaping, an ultrasonic device (Ultra X, Eighteeth, China) was used to activate 3% sodium hypochlorite and 17% ethylenediaminetetraacetic acid (EDTA) approximately for 1 min to remove the smear layer and existing debris from the root canals. Normal saline was used as an intermediate solution between the 3% sodium hypochlorite and 17% EDTA (SmearClear™, Kerr Dental, Orange, California). The root canals were dried entirely with sterile paper points. The prepared root canals were obturated with an appropriate tapered gutta-percha cone (Coltene Whaledent, Switzerland) and bioceramic sealer (CeraSeal, Meta Biomed, Europe) using a single-cone obturation technique. The gutta-percha cones were later sheared off at the level of the orifices with a touch-and-heat device, and the remaining sealer was removed with an ultrasonic scaler. An immediate postoperative radiograph revealed well-obturated four distinct root canals [Figure 9]. A temporary restoration with Intermediate restorative material (IRM) (Dentsply DeTrey, Konstanz, Germany) was placed to seal the pulp chamber, and the patient was recalled after 1 week for the permanent restoration. After 1 week of observation, the patient showed no spontaneous pain, no pain with hot or cold stimulation, and no apparent abnormalities in the buccal or lingual mucosa. On the same appointment, the postendodontic restoration was performed with composite (Dentsply Maillefer, Ballaigues, Switzerland). A 1-year follow-up of the case revealed no spontaneous pain, and the radiograph showed no secondary caries, fracture, or apical radiolucency [Figure 10].

Figure 5

Working length of the mesial root showing two root canals

Figure 6

Working length of the distal root showing two root canals

Figure 7

Master cone radiograph of the mesial root

Figure 8

Master cone radiograph of the distal root

Figure 9

Postoperative radiograph taken immediately after obturation clearly shows four root canals

Figure 10

One-year follow-up radiograph

DISCUSSION

Despite the current evidence suggesting that taurodontism is highly prevalent in mandibular molars, the present case revealed an unusual finding of taurodontism on a mandibular first premolar with two roots and four canals. Taurodontism is caused by the failure of Hertwig's epithelial root sheath to invaginate to the proper horizontal level, resulting in a tooth with short roots, an elongated body, and an enlarged pulp chamber.[3] The external morphology of the tooth remains normal, and taurodontism can only be diagnosed by radiography. Since it can be challenging for clinicians to locate, negotiate, clean, shape, and obturate the root canals, taurodontism may compromise the treatment outcome. A tooth with taurodontism may possess a complex root canal morphology, which makes performing endodontic procedures complicated.[78]

Shifman and Chanannel employed a taurodontic index (TI) based on three measurement variables on a radiograph to diagnose taurodontism. For a tooth to be considered taurodontism, the TI, which is defined as the ratio of the distance between the chamber roof to the floor and the chamber roof to the root apex, must be >20, and the distance between the pulp chamber floor and the CEJ should be >2.5 mm. The degrees of taurodontism were also determined to be either hypotaurodontism if the TI is 20–30, mesotaurodontism if the TI is 30–40, or hypertaurodontism if the TI is 40–75.[9] The present case met the taurodontism requirements, and the tooth was classified as a mesotaurodontism since the TI value was approximately 40, and the distance from the pulp chamber floor to the CEJ was about 5 mm.

According to MacDonald-Jankowski and Li, ethnic Chinese females have a higher prevalence of taurodontism than other ethnic groups.[10] The majority of the cases of taurodontism were found in permanent mandibular molars.[3] Based on an in vitro study, Madeira et al. reported that the prevalence of taurodontism in mandibular first premolars was 0.42% in mandibular first premolars.[11]

A preoperative radiograph was taken at an angle of 15°–20°, either mesially or distally from the horizontal long axis of the tooth, which is required to diagnose the multiple roots and canals.[12] On the other hand, conventional radiographs have constraints that limit the preservation of details about the tooth, such as compression of three-dimensional anatomy, image distortion, and superimposition of anatomical features. Therefore, CBCT would be an ideal imaging modality, allowing clinicians to view the area of interest in multiple planes and formulate treatment planning.[13] In the present case, a CBCT scan of tooth 21 confirmed a deep, extended pulp chamber with two roots and four root canals in the axial and sagittal sections.

Root canal treatment of such a tooth becomes challenging due to inadequate illumination and poor visibility of root canal orifices. Furthermore, excessive bleeding during cavity access, unpredictability of chemical disinfection of the complex pulp-radicular system, and mechanical preparation of thin canal walls are some of the obstacles that make taurodontic tooth management extremely difficult for operators.[14] To address the aforementioned issue as well as the small dimensions of the first premolar, the entire procedure was carried out under a DOM.

The root canal orifices were refined by careful troughing with the ultrasonic device under magnification to avoid procedural errors such as perforation. Ultrasonic tips should be used with a light touch and kept moving while in use, beginning with the lowest power setting and gradually increasing if necessary. Using an intermittent coolant such as water prevents the tip from overheating and eliminates debris, but it also obstructs the clear vision of the operating field.[15] In the present case, a long and thin ultrasonic tip was used to improve the visibility of the working area with intermittent water spray.

It is advocated that the root canals should be prepared to the optimum size to ensure effective cleaning and minimize the bacterial load in infected root canals. For most posterior teeth, a preparation size of 20–40 K files seems to be sufficient and can preserve the radicular dentin.[16] The use of files with 4% taper would be more conservative to the tooth structure than files with 6% taper. Endodontic files with greater taper will result in excessive removal of the dentinal tooth structure, increase the likelihood of strip perforations, and subsequently lead to vertical root fractures in future.[1718] Considering that the present case consisted of four root canals, all canals were shaped to size 25 with 4% taper rotary files for a more conservative approach. Furthermore, a bioceramic-based root canal sealer was used in the current case due to its excellent bioactivity, biocompatibility, and sealing capacity in the root canals, as a hermetic seal is warranted for an excellent long-term prognosis of endodontically treated teeth.[19]

Even though, the 1-year follow-up periapical radiograph of the present case revealed no signs of periapical pathology, the authors would like to comprehend the significance of continuing clinical and radiological follow-ups for endodontically treated teeth. In addition, according to the Endodontic Case Difficulty Assessment Form and guidelines proposed by the American Association of Endodontists, the mandibular first premolar in the present case could be categorized as extremely difficult. Hence, a taurodontic mandibular first premolar with two roots, bifurcation around the middle third of the root with four root canals, and complex root canal anatomy were among the challenging criteria, in this case, making it highly intriguing and potentially one of the rarest occurrences. Notwithstanding, a literature search indicated that few cases of taurodontic mandibular first premolars are reported [Table 1]. The authors believe that such a case report will offer valuable insight into the field of endodontics.

Table 1

Summary of the published case reports on the root canal morphology of the mandibular first premolar (from 2000 to 2021)

Study	Number of roots	Root canal anatomy	Diagnostic method	Taurodontism
Milano M et al.[20]	2	Not available	Radiographic	Not available
Moayedi S et al.[21]	2	3 root canals	Radiographic	X
Poorni S et al.[22]	2	3 root canals	Radiographic	X
Kararia N et al.[23]	2	2 root canals	Radiographic	X
Vaghela DJ et al.[24]	4	4 root canals	Radiographic	X
Izaz S et al.[25]	2	4 root canals	CBCT	X
Shen LC et al.[26]	1	4 root canals	CBCT	√
Zhang M et al.[27]	1	5 root canals	CBCT	X

X: Taurodontism is not seen, √: Taurodontism seen

CONCLUSION

The mandibular first premolar, which is often regarded as an enigma to endodontists, exhibits fascinating anatomic variations, as demonstrated in the present case. As per our knowledge, this is the first reported case of a taurodontic mandibular first premolar with two roots and four canals successfully managed using CBCT and DOM. The clinician must be vigilant, as variations of root and canal anatomy might be encountered at any time during treatment. In endodontically challenging cases, the use of CBCT imaging and DOM can help clinicians understand the complex root canal anatomy so that they can explore the root canal system and clean, shape, and obturate more efficiently.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.