Case Report: Uncommon Maxillary Lateral Incisor with a Type 3 Invagination and C-Shaped Root Canal System

C-shaped root canal systems are occasionally found in mandibular molars and, very rarely, in maxillary molars.¹ However, Boveda et al published a report of an unusual case of a C-shaped root canal system in a maxillary left lateral incisor.² One investigator reported that of 100 maxillary lateral incisors examined, none demonstrated any evidence of dens invaginatus (DI).³

According to Oehlers, there are three types of DI.⁴ Type 1 is an invagination confined to the crown only. Type 2 involvement extends past the cementoenamel junction to the root, but not to the periapical region. Type 3 is the most complex condition, in which the invagination extends to the periapical region and may exhibit a “second foramen.”⁴

Palatal grooves or DI can present difficult diagnostic and treatment challenges.^5,6 The incidence of this condition ranges from 1.9% to 8.5%.^7,8 Kramer and Everett reported that the incidence of a palato-gingival groove extending to the apex in maxillary lateral incisors is 0.5%.⁷

The etiological mechanism for DI is unclear, but some authors have postulated that this malformation probably results from an infolding of the dental papilla during embryological development.⁹ The prognosis for successful treatment of these teeth is generally poor.⁶

A recent report demonstrated an apparently successful treatment of a maxillary lateral incisor exhibiting DI, which could not be placed in any specific category according to Oehlers classification, even though invagination invaded the root similar to either Type 2 or Type 3.⁹

This case report discusses a failed attempt to successfully treat a Type 3 DI maxillary lateral incisor with C-shaped canal anatomy due to failure to appreciate the complexity of the anatomy and failure of the patient to follow-up with necessary periodontal treatment. The authors are not aware of any reports in the literature involving this type of unusual configuration in maxillary lateral incisors prior to 1999.²

In December 2006, a 21-year-old female patient reported to the emergency clinic at University of Missouri-Kansas City School of Dentistry with a chief complaint of constant pain of moderate intensity in the right maxillary incisor area for the previous 3 weeks. Medical history was noncontributory. No intraoral swelling or sinus tract was present. Radiographically, there was evidence of periapical radiolucency and a radiolucent line suggesting DI involving tooth No. 7. Teeth Nos. 6, 8, and 9 responded within normal limits (WNL) to cold thermal testing with Hygenic^® Endo-Ice^® (Coltène/Whaledent Group, www.coltene.com). Tooth No. 7 was nonresponsive. Sensitivity to percussion and palpation was demonstrated only on tooth No. 7. The pulpal diagnosis was necrotic pulp No. 7, with a periradicular diagnosis of chronic apical abscess (CAA). Periodontal probing revealed a 5-mm pocket on the palatal aspect corresponding to a palatal groove. A periodontal consult was requested. Flap surgery with an attempt at re-contouring and restoration of the palatal groove, as well as possible osseous graft in the bony defect, were recommended following endodontic treatment. The patient was informed of the uncertain prognosis and agreed to the exploratory surgery following endodontic therapy (Figure 1).

The next day, root canal treatment was accomplished in a single visit. Only one root canal system was located using the dental operating microscope (DOM). The canal was cleaned and shaped to a size 35/.04 taper using nickel-titanium rotary instruments and obturated with gutta-percha by warm vertical compaction (System B™ and Obtura, SybronEndo, www.sybronendo.com; Obtura Spartan Endodontics, www.obtura.com) and root canal sealer (ThermaSeal^® Plus, DENTSPLY Tulsa Dental Specialties, www.tulsadentalspecialties.com). A slight groove was visualized through the DOM on the disto-palatal portion of the canal, but no communication with the palatal groove was evident. A sterile cotton pellet was placed, and the access opening was sealed with temporary cement.

Following obturation, this “grooved” area was visualized radiographically as an area in the middle third of the root, where some sealer and gutta-percha appeared to slightly fill in the anomalous groove (Figure 2). The patient was then referred to the Department of Periodontics to proceed with the planned surgical correction of the anomalous groove.

Unfortunately, the patient did not comply regarding treatment in the periodontal department and was not seen again seen until February 2009, when she appeared in the emergency clinic at the University of Missouri-Kansas City School of Dentistry with a chief complaint of spontaneous intense pain in the right maxillary and mandibular quadrants of 1-week duration. Neither temperature, palpation, nor percussion was an issue. She had seen her general practitioner earlier, but he had been unable to make a diagnosis and, therefore, referred her to the university’s School of Dentistry emergency department.

Radiographic examination was WNL for all teeth in both quadrants with the exception of the maxillary right lateral incisor (No. 7), which revealed that the previous radiolucency had increased in size and extended to mid-root on the distal aspect of the tooth. All other teeth in both right quadrants exhibited shallow or no restorations with no visible cracks or wear facets.

Cold thermal testing and electric pulp testing in both right quadrants was WNL, with the exception of No. 7, which did not respond to pulp testing. Percussion and palpation in both quadrants were also negative (Figure 3).

Since all diagnostic tests were WNL and the patient was in moderate to severe pain, the decision was made to perform a diagnostic anesthetic injection over the maxillary right lateral incisor to observe what effect this would have on her pain. One carpule of local anesthetic with epinephrine 1:100,000 was deposited at the apex of the maxillary right lateral incisor. Within 1 minute, all of the patient’s pain abated. Based on this finding and the periradicular lesion of increased dimension, the authors concluded that tooth No. 7 was the source of the patient’s pain.

She was offered the options of nonsurgical root canal retreatment, surgical re-treatment, or extraction. The patient informed the authors that she was tired of dealing with this tooth and if she could not be guaranteed a 100% success rate upon treatment, she preferred that the tooth simply be extracted. The authors complied and extracted the tooth.

Following extraction, the tooth was stained with methylene blue dye and sectioned. Figure 4 and Figure 5 reveal the maxillary right lateral incisor with an Oehlers Type 3 DI and what appears to be a “C”-shaped canal system “wrapped around” the invagination. Figure 6 shows a cross-section of the tooth illustrating the unusual C-shaped configuration of the canal system.

Nonsurgical root canal therapy was performed on a maxillary right lateral incisor. The patient did not follow-up with planned periodontal treatment for surgical resolution of the palato-gingival groove. Ultimately, the tooth was extracted due to nonrestorable periodontal disease. The extracted tooth was sectioned and stained, revealing a very complex C-shaped root canal system and invagination that may well have been refractory to any form of endodontic or periodontal corrective treatment.

Closer examination at diagnosis may have revealed the DI Type 3 and saved both the clinician and patient the time and trouble rendered in a futile attempt to salvage what turned out to be a badly compromised maxillary lateral incisor. The morphological complexities of a tooth with DI may thwart the best possible endodontic and periodontal therapy.

Based on the findings described above and given the complexity of the canal system in this case, it is highly doubtful that any type of conventional or surgical treatment would have saved this tooth unless all canal portions could have been accessed and treated. The unique C-shaped anatomy was apparently created by the invagination, which made the smaller C-shaped portion of the canal inaccessible for endodontic treatment. Even though the operator was using a dental operating microscope, this portion of the canal was not visualized or treated. However, had the entire system been cleaned and shaped, the success of the case would have been dependent on compliance of the patient to follow-up with the periodontal treatment as recommended.

Having a knowledge of the complexity of the canal system in a tooth such as this may enable a more predictable endodontic outcome. Assuming patient compliance with the periodontal treatment, it is believed that successful retention of this unusual tooth could have resulted.

Ronald R. Riley, DDS
Clinical Assistant Professor
Department of Endodontics
University of Missouri School of Dentistry
Kansas City, Missouri

James A. Dryden, DDS, MS
Former Clinical Professor and Chair
Department of Endodontics
University of Missouri School of Dentistry
Kansas City, Missouri

Private Practice
Joplin, Missouri

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