Endodontic Management of Three-Canalled Mandibular Lateral Incisor Using Dental Operating Microscope

Abstract

This case report presents endodontic management of a mandibular lateral incisor with three canals using surgical dental operating microscope. This study describes the root canal variation of mandibular lateral incisor and highlights the importance of surgical operating microscope in detecting an unusual canal morphology.

INTRODUCTION

Inadequate knowledge of tooth morphology and canal systems may pose significant problems during root canal treatment [1]. To ensure the long-term prognosis of a tooth undergoing root canal treatment, it is imperative to assess the anatomy of the root canals and their numerous variations before initiating root canal treatment [2,3].The root canal anatomy of the mandibular lateral incisor usually has a single root with a single canal. Among the variations, the presence of an additional (lingual) canal is the most common. The incidence of the lingual canal has been reported as 44% [4,5]. Although a high incidence of a lingual canal has been reported, the majority of these canals will join and exit in a single foramen in 70% of the cases [4,6,7,8].

Few anomalies have been reported for the mandibular lateral incisor in the dental literature. Some of them include dens invaginatus [9,10], fusion and germination [11]. The most common variation found in the mandibular lateral incisor is the presence of a second canal (lingual). Table 1 highlights various studies published on the root canal anatomy of mandibular lateral incisors.

Table 1.

In-Vitro Studies on Root Canal Aberrations of Mandibular Lateral Incisors

Authors	Type of Study	Country	One Canal (%)	Two Canals (%)	Three Canals (%)
Vertucci (7)	Clearing	USA	98	2	-
Pineda and Kuttler (8)	Radiographic	Mexico	98.7	1.3	-
Caliskan et al. (3)	Clearing	Turkey	98	2	-
Sert and Bayirili (6)	Clearing (Men)	Turkey	90	10	-
	Clearing (Women)	Turkey	90	10	-
Walker (21)	Radiographic	China	99	1	-

The introduction of the dental operating microscope has revolutionized endodontic treatment. A microscope is the best tool in visualizing intricate dental anatomies otherwise not visible to the naked eye. The benefits of root canal procedures completed with a microscope include [4]:

• Magnified image

• Increased precision

• Improved illumination

• Improved visualization

On a thorough literature search it was observed that there has been no in-vitro or clinical case reports of a mandibular lateral incisor with three canals.

The present case report discusses the successful endodontic management of a three-canalled mandibular lateral incisor.

CASE REPORT

A 58-year-old woman was referred to the Department of Conservative Dentistry and Endodontics with the chief complaint of pain in her lower front teeth region.

The patient’s medical history was noncontributory.

Dental history revealed dull, continuous pain in the left mandibular lateral incisor (teeth #23) for the past 1 month. On clinical examination, tooth #23 had a large proximal restoration and was tender on percussion (Fig 1A). Palpation of the labial and lingual aspect of the teeth did not reveal any tenderness. The tooth was immobile and periodontal probing around the tooth was within physiological limits.

Fig 1.

A, Pre-operative radiograph of tooth #23; B, Access opening of tooth #23 under dental operating microscope; C, Master cone radiograph; D, Obturation of tooth #23

No response was elicited in the tooth with the electronic pulp tester (EPT) (Parkel Electronics Division, Farmingdale, NY) and thermal (heat and cold) pulp vitality testing methods (Dentsply Maillefer, Ballaigues, Switzerland).

A pre-operative radiograph revealed large proximal restoration close to the pulp space with periodontal ligament widening related to the left mandibular lateral incisor. Based on clinical and radiographic findings, a diagnosis of pulpal necrosis with symptomatic apical periodontitis was made for tooth #23. Tooth #23 was anesthetized with 1.8 mL (30 mg) 2% lignocaine containing 1:200,000 epinephrine (Xylocaine; AstraZeneca Pharma Ind Ltd, Bangalore, India) followed by rubber dam isolation. After access cavity preparation using a round carbide no #2 (MANI Inc, Toshigi-Ken, Japan), one labial and one lingual canal was identified in tooth #23, but on examination under surgical operating microscope (Seiler Revelation, St Louis, MO), an additional canal was located between the labial and the lingual canal (Fig 1B).

This additional canal was initially negotiated using a C+ file ISO #8 (Dentsply Maillefer, Ballaigues, Switzerland). The working length was determined in all three canals using an apex locator (Root ZX; Morita, Tokyo, Japan) and was later confirmed by a radiograph. Coronal orifice opening was performed using Gates-Glidden drills No.2 and No.1 followed by cleaning and shaping with 2% stainless steel hand K-files up to ISO #30 (MANI Inc, Toshigi-Ken, Japan) using a crown-down technique. Irrigation was performed with 2.5% sodium hypochlorite and normal saline solution. Final irrigation was performed with 17% EDTA solution. Calcium hydroxide paste (RC CAL, Prime Dental Products Pvt Ltd, Mumbai, India) was used as an intracanal medicament for a period of one week.

On the next appointment, the patient was asymptomatic. Calcium hydroxide paste was removed using ultrasonics. A master cone radiograph was taken to confirm the working length (Fig 1C). The canals were then dried with absorbent points (Dentsply Maillefer, Ballaigues, Switzerland), and obturation was performed using cold lateral compaction of gutta-percha (Dentsply Maillefer, Ballaigues, Switzerland) and AH Plus resin sealer (Maillefer, Dentsply, Konstanz, Germany) (Fig. 1D). The tooth was then restored with a posterior composite resin core (Z350; 3M Dental Products, St Paul, MN). The patient was asymptomatic during the 6-month follow up.

Tooth #26 that was also endodontically treated simultaneously had one buccal and one lingual canal. Endodontic treatment for tooth #26 was performed similar to that of tooth # 23.

DISCUSSION

Failure to identify extra canals is one of the most common reasons for the failure of endodontic treatment [12].

According to a recent study conducted by Song et al., missed canal is the second most common reason for failure of endodontic treatment [13]. Multiple angulated pre-operative radiographs can help us identify complex root canal anatomies of the root canal system and thereby reduce the incidence of missed canals during routine endodontic therapy [14]. Use of higher investigation tools such as cone beam computed tomography (CBCT) has also been suggested for better understanding of the aberrations in the root canal anatomy [15,16]. Even though use of CBCT involves less radiation than conventional CT, the radiation dose is still higher than regular conventional intraoral radiographs [17].

In our case report, an additional canal was found between the labial and the lingual canal. This additional canal was termed as the mid-labio-lingual (MLL) canal. This MLL canal was clearly distinguishable on examination under the surgical dental operating microscope. Use of the surgical operating microscope is indispensible in the field of endodontics. Matherne et al. [18] suggested the use of CBCT and surgical microscope to successfully diagnose various aberrations in the root canal anatomy. Sabala et al. [19] reported that in 60% of the cases, bilateral symmetry of variation is usually observed. He also stated that as the aberration increases, it is more likely to be bilateral in occurrence. In the present case report, all the three canals joined in the apical third of the root canal and exited as a single apical foramen. This pattern of root canal configuration is classified as type-I canal pattern according to a study conducted by Gulabivala et al. [20] and type- XVIII canal pattern based on a study performed by Sert and Bayirli [6].

Many mandibular incisors have two canals, which may merge into one canal before reaching the apex. In rare cases, separate foramina may form. In a radiographic study of 364 specimens, Benjamin and Dowson reported that 41.4% of the mandibular incisors had two separate canals; of which only 1.3% had two separate foramina [22].

Young et al. successfully managed three mandibular incisors with two separate canals and foramina. They suggested that manual exploration of the root canal system with an endodontic file or explorer is a reliable way to identify the exact configuration of the root canal, especially the number of foramina [23]. Kartal et al. studied the root canal morphology of 100 mandibular incisors and showed two additional canal configurations other than Vertucci’s classification [24]. Type 6 was a newly defined canal configuration in which two separate canals leave the pulp chamber, a new tiny canal leaves the lingual canal in the middle third and comes to the midline, goes down to the apical third, and all of the canals merge together and constitute one canal joining at the apex. Type 7 was also newly defined.

After leaving the pulp chamber as a wide single canal, division occurs into two canals in the middle third.

These canals then rejoin into a single canal that splits again and exits as three separate foramina. Miyashita et al. showed that mandibular incisors possess a flat root that is longest in the labio-lingual direction, and furcate and ribbon-like canals occasionally appear in the center of the root. Therefore, the problem exists for instrumentation of the labio-lingual wall of ribbon-like root canals and also clinically it is almost impossible to discriminate between separate canals and ribbon-like canals [25]. Fortunately, only 3.1% of the samples have separate canals to two apical foramina. Therefore, authors suggest the use of circumferential filing rather than circular filing to prevent incomplete cleaning and shaping of the root canal system.

CONCLUSION

The present case report describes the endodontic management of a mandibular lateral incisor with three root canals. It highlights the importance of the dental operating microscope in detecting extra canals for successful endodontic treatment.