BACKGROUND

The main objective of root canal treatment is thorough shaping and cleaning of the entire pulp space and its complete obturation with an inert filling material.¹ The main reason for the failure of root canal treatment is the inadequate removal of pulp tissue and microorganisms from the root canal system.² Therefore, it is imperative that the clinician must have a thorough knowledge of root canal morphology and its possible variations to achieve a high level of success.

The root canal system has anatomic complexities in the form of additional canals, intercanal communications, lateral canals, and multiple foramina. Usually, mandibular first molar has two roots; mesial and distal with two canals in mesial and one canal in the distal root.^3,4 The mesial root of mandibular molars often shows an additional canal in the form of MM canal.^5-12 Clinical studies have investigated the incidence of MM canals in mandibular molars. Before the introduction of cone beam computed tomography (CBCT), the incidence of MM canal ranged between 1 and 15%,^5,10,13 whereas a recent study⁷ has reported a much higher incidence of 46.2% in mandibular first and second molars. Use of CBCT to identify root canal system has been supported by Matherne et al.¹⁴ A micro-CT study by Harris et al¹¹ reported 36% of mandibular first molars with more than two canals in the mesial root. Troughing in the floor of the pulp chamber and visualization through the dental operating microscope have been proposed by many authors as an effective and safe approach to examine the mesial root for the potential MM canal.^7,12 In addition to the MM canal, very few cases have reported a third canal located in the distal root. The incidence of the MD canal is very rare and found to be 0.2 to 3% of the reported cases.^15-21 The purpose of this article is to report the successful treatment and follow-up of mandibular first molar with three mesial and three distal canals.

CASE REPORT

A 29-year-old white male patient presented to the clinic with a complaint of intermittent pain on the lower left side of the face since 2 months, getting worse with cold drinks. The medical history was noncontributory, and the patient reported a history of multiple fillings. Clinical examinations revealed composite restoration on tooth #19 and pain on percussion. The cold test was positive with an exaggerated response. Periapical X-ray film (Fig. 1A) showed widened periodontal ligament space and radiopaque lesions around both mesial and distal roots of tooth #19. The diagnosis of symptomatic irreversible pulpitis with symptomatic apical periodontitis and condensing osteitis was made. Nonsurgical root canal treatment was planned, and informed consent was obtained.

One carpule of lidocaine local anesthesia, 0.036 mg of epinephrine was administered, and rubber dam isolation was done. Under dental operating microscope (Zeiss OPMI pico, Carl Zeiss Surgical, Germany) at ×8 magnification, the pulp chamber was accessed using a sterile round bur and ultrasonic tips. Initially, four canal orifices were identified as mesiobuccal (MB), mesiolingual (ML), distobuccal (DB), and distolingual (DL). The patency of canals was confirmed with #10 K-file and orifices of all four canals were opened using Gates Glidden drills #2 and #3. Working length was determined, and canals were instrumented with Protaper Next (Dentsply maillefer, Switzerland) rotary files number X1 and X2. Canals were irrigated with 3% sodium hypochlorite after each instrument. The canals were dried; calcium hydroxide was applied as an intracanal medicament and cavity was restored with intermediate restorative material (IRM) (Dentsply Caulk, Milford, USA) temporary restorative material.

About 10 days later, the patient reported with lesser symptoms, but the tooth was still tender to percussion. Cold test gave a positive response. After profound anesthesia and rubber dam isolation, temporary filling was removed. Under dental operating microscope using ultrasonic tips, troughing was performed in the line between MB and ML; DB and DL. Additional canals were located as MM and MD (Figs 1B and C). The apical patency was confirmed; cleaning and shaping procedure was performed for both the MM and MD canals. The canals were dried; calcium hydroxide was applied in all the six canals and cavity was restored with IRM temporary restorative material. The patient was scheduled for another appointment after 2 weeks for obturation, but the patient missed the appointment and reported 5 months later. The tooth #19 was asymptomatic ever since the last visit. On examination, IRM temporary restoration was intact with no tenderness on percussion. After profound anesthesia, rubber dam was inserted and temporary filling was removed. Calcium hydroxide was flushed out of all six canals, and the canals were dried. Appropriate sized gutta-percha cones were inserted into the canals, and a radiograph was taken (Fig. 1D). Radiograph showed all the six canals as independent, and there was no connection. The canals were obturated with gutta-percha and epoxy resin sealer (AH Plus) (Dentsply DeTrey GmbH, Konstanz, Germany) by warm vertical compaction technique up to the level of the orifices (Figs 2A and B). A sterile cotton and IRM were inserted in the chamber as a temporary restoration, and the occlusion was checked. Postoperative radiograph (Fig. 2C) showed homogenous obturation in all six canals, and lesser bone densities around mesial and distal roots compared with 5 months old preoperative radiograph. Postoperative instructions were given; the patient was referred back to his dentist for final restoration, and a 12-month follow-up appointment was scheduled.

The patient came for the recall visit after 1 year and 9 months since completion of root canal treatment. His medical history was unchanged, he had no symptoms, and tooth #19 responded within normal limits. The IRM was still in the access cavity and had not been replaced with the final restoration. Radiograph showed normal periapical tissues and normal trabecular pattern (Fig. 2D). Importance of final restoration was discussed with the patient and he had been advised to get it restored as early as possible.

DISCUSSION

Numerous cases are reported in the literature regarding the unusual anatomy of mandibular first molar.^5-12,15-21 The detection of additional canals requires thorough knowledge of root canal morphology and its frequent variations. Careful examination of the pulpal floor, selective troughing, and better visualization through a dental operating microscope are essential for the detection of additional canals in a mandibular first molar.^7,12 In a study by Azim et al,⁷ the MM canal was found in 46.2% cases, out of which 6.6% were located after conventional access preparation and 39.6% after standardized troughing. They also reported significantly higher incidence of an MM canal in the younger patient age group. In the present case, the patient reported with lesser symptoms and the cold test gave positive response after initial cleaning and shaping, which gave possibilities of additional canals. The selective troughing in both mesial and distal roots and better visualization through a dental operating microscope helped to locate additional MM and DM canals. Wallance and Baugh ²² reported a case of MM canal in the mandibular first molar, where MM canal originated as a separate orifice, but joined in the apical third of the canal. Izaz et al²⁰ reported a case of MD canal that joined the main canal in the apical third. However, in this case, both MM and DM canals originated as separate orifices and remained separated throughout the entire length of the canal.

Figs 1A to D

(A) Preoperative radiograph of mandibular first molar showing occlusal restoration, widened periodontal ligament space, and radiopaque lesions around both mesial and distal roots; (B) access cavity showing three mesial canals; (C) access cavity showing three distal canals; and (D) master cone radiograph showing gutta-percha in six separated canals

Figs 2A to D

(A) Access cavity showing three mesial canals obturated with gutta-percha and epoxy resin sealer up to the level of the orifices; (B) three distal orifices obturated up to the level of the orifices; (C) postoperative radiograph showing homogeneous obturation of all the six canals; and (D) follow-up radiograph showing normal periapical tissues and normal trabecular pattern

CONCLUSION

Ability to disinfect the root canal system is of paramount importance in endodontic treatment. Achieving a complete sterilized environment is not always possible due to the presence of additional canals, lateral canals, ramifications, and intracanal connections. Careful interpretation of symptoms combined with thorough examination of access cavity under the dental operating microscope significantly decreases the chance of missing these hidden anatomies.

CLINICAL SIGNIFICANCE

Although the anatomy of the tooth in this report is not usual and can be found rarely, clinicians should be aware of this variability of the root canal morphology to avoid treatment failures. All possible attempts should be made to locate and treat the additional canals in the mandibular first molar to achieve a higher level of success.