Type II canal configuration and Type I Dens invaginatus.

The prevalent notion about maxillary central incisor with normal external morphology is a tooth with single root and root canal. A case in which all four maxillary incisors were having Type II canal configurations (Vertucci's classification) is reported, in addition, the lateral incisors revealed dens invaginatus with a Type I pattern as suggested by Ohler's classification and a large periapical lesion was seen in relation to the right lateral incisor. The diagnosis was confirmed with the aid of spiral computed tomography (CT) and canals obturated. Nonsurgical healing of the lesion was assessed by reviewing the case at prefixed intervals of time.

INTRODUCTION

The maxillary central incisor shows lateral canals in over 60% of the cases, in contrast, the occurrence of true second canals is quite rare.[1] Rather than the instrumentation techniques during cleaning and shaping, the original canal configuration significantly influences the changes during the preparation.[2] The simplest classification system was proposed by Weine, where the root canal configuration is divided into four basic types,[3] whereas, Vertucci had demonstrated eight types of canal outlines utilizing staining technique for pulp cavity.[4] Kartal and Yanikoglu,[5] and Gulabivala et al.,[6] also contributed to the existing literature by demonstrating additional types of canal configurations. As per Vertucci's study, the possibility of maxillary incisors and canines having Type II canal configuration was almost nil.[4]

Though the literature on anomalous canal and root morphology in maxillary central incisors is scarce, the maxillary lateral incisor is well-known for its embryologic anomalies such as germination, fusion, radicular grooves, dens invaginatus, etc. The reported incidence of dens invaginatus ranges from 0.04 to 10%.[7] Even though a number of case reports have been published on Type II and Type III dens invaginatus (classification proposed by Ohler),[8910] literature is sparse on the pulpal and periapical involvement of Type I or mild form of dens invaginatus where the invagination is usually confined to crown. Schmitz et al., has described successful management of a case of Type I dens invaginatus with open apex and periradicular lesion.[11]

CASE REPORT

A 28-year-old south Indian native female presented with a complaint of localized pus discharge and large swelling on palatal aspect of right maxillary incisors of about 3 weeks’ duration. The symptoms started as occasional numbness in relation to the right upper lateral incisor since about 1 year and there was no history of trauma. Clinically, the tooth was normal in appearance without any mobility or pain; no discoloration, cracks, or fracture lines were detected for any of the anterior teeth. It was further noted that both right and left maxillary lateral incisors had prominent cingulum resembling a form of dens invaginatus [Figure 1a]. Diagnostic intraoral periapical radiograph showed large irregular radiolucency of size 2 × 3 cm size involving the apices of right central and lateral incisors. Moreover, all the incisors had two separate canals arising in pulp chamber and reuniting in the root canal to have a single exit [Figure 1b]. Both central and lateral incisors on right side were found to be nonresponsive for vitality test using EndofrostTM refrigerant spray (Coltene/Whaledent, Germany). Results of electric pulp testing were not consistent and a test cavity preparation was done for the teeth in question without local anesthesia under air water spray and the response was null. Based on the clinical and radiographic findings, it was decided to proceed with endodontic treatment on both central and lateral incisors.

Figure 1

(a) The lateral incisors with prominent cingulum and palatal swelling in relation to right lateral incisor. (b) Intraoral periapical (IOPA) showing Type II canal configuration of incisors with large periradicular lesion in relation to right central and lateral incisors. (c) Clinical view after access cavity preparation showing mesiodistally located canals in central incisors. (d) Computed tomography (CT) image showing mesiodistally located canals in central incisors bilaterally. (e) CT image showing buccolingually located canals bilaterally in lateral incisors. (f) IOPA 1 year after obturation

The presence of two canal pattern was made sure with tube shift method radiography. The access cavity preparation was proceeded under direct vision and locating the orifices of central incisor was relatively effortless compared to lateral incisor; and the orifices were located mesiodistally [Figure 1c]. For lateral incisor, one lingual pit was noticed in access cavity in addition to the buccolingual canal orifices, suggesting this tooth as a mild form of dens invaginatus. After locating the canals and instrumenting to an approximate working length, infected tissue fluid started expressing through the orifices of the lateral incisor (and never through central incisor) suggesting this tooth as the focus of infection. Sodium hypochlorite (5.25%) has been used as intracanal irrigant and cleaning and shaping was completed for all the canals. Because of the very rare nature of the case complicated by internal Type II canal configuration and external morphology of dens invaginatus, it was decided to take a spiral CT for confirmation of internal anatomy and comparison with contralateral incisors. This was necessitated, as we were planning for the nonsurgical healing of the lesion. The CT examination revealed that for both the central incisors, canals were located mesiodistally [Figure 1d], whereas, it was located buccolingually for both lateral incisors [Figure 1e].

After drying the canal, calcium hydroxide medicament was coated on the walls of root canals with the help of paste carrier. Coronal orifice was sealed with zinc oxide eugenol restoration. In the subsequent appointment, after 1 week a fresh calcium hydroxide medicament was placed inside the root canals of both central and lateral incisors. In spite of the canal debridement and weekly renewal of the calcium hydroxide in three subsequent appointments, expression of infected tissue fluid through the orifice of lateral incisor had not regressed. Hence, the treatment plan was modified and a combination of minocyclin, metronidazole, and ciprofloxacin antibiotic paste was placed in the draining canal. Following this, the palatal swelling decreased in size and the canals of lateral incisor appeared dry without fluid discharge. Obturation was performed with conventional Gutta-percha points using lateral compaction technique with zinc oxide-eugenol cement as sealer. Access cavity was sealed with glass ionomer cement over which composite restoration has been given. The patient was recalled at regular intervals of 1, 3, 6, and 12 months and review radiograph 1 year after surgery showed excellent healing of periapical pathology as evidenced by decrease in size of the lesion with appearance of bony trabeculations [Figure 1f].

DISCUSSION

The prevalence of lateral canals, additional abnormalities in crown root morphology and corresponding root canal variations have been amply reported. However, to the best of our knowledge, the presence of Type II canal configuration in maxillary centrals and laterals has not been reported yet. According to Weine, the incidence of Type II canal configuration is highest in mesial root of mandibular molar followed by premolars. In the present case, this configuration was noted in both the central and lateral incisors, which is a first of its kind. Here, the canals were meeting in the middle third 6-7 mm below the apex and this could be due to the fact that more closer the position of coronal orifices, higher the probability of uniting at a more coronal position in the root canal. Considering the mesiodistal width of pulp chambers of incisors, this fact is easily explainable compared to that of posterior teeth where the two canals meet more apically. The access cavity as well as subsequent instrumentation has been carried out with an attempt to preserve the maximum dentine thickness as possible, but without compromising cleaning and shaping.

Dens invaginatus is a developmental malformation resulting from invagination of the enamel organ into the dental papilla beginning at the crown and sometimes extending into the root before mineralization phase. A simple and common classification by Ohler divides them into three types: Type I, where the invagination is confined to crown with a lingual pit formation; Type II having deeper invasion into the root (extending beyond cementoenamel junction), which may remain as a blind sac and may not always communicate with the main canal; and Type III, a form which penetrate through the root and communicate laterally with the periradicular tissues or open into apical part of the root. The incidence of dens invaginatus has been reported highest in maxillary lateral incisors with a Type I pattern.[12] Histological studies had shown intact dentine, presence of vital connective tissue or even fine canals with communication to the pulp in the invagination.[13] It has been suggested that the thin enamel at the invagination may break down and microorganisms may gain entry to the pulp by invading dentinal tubules.

In an attempt to gain root wall thickness and to a lesser extent, continued root development, conventional apexification procedures in necrotic immature teeth are replaced with regenerative endodontic procedures. Yang et al., has described such an innovative and conservative procedure in the management of Type II dens invaginatus with periapical lesion by sealing the invagination and successful revascularization in main canal.[14] In spite of the bilateral presence of dens invaginatus in many of the reported cases, pulpal and periapical involvement was limited to tooth on one side; a fact which is not yet explained. An isolated case of the management of Type II dens invaginatus in calcified maxillary lateral incisor has been demonstrated recently by Subbiyya et al.[15]

In the present case, the lateral incisors had Type I dens invaginatus combined with Type II canal configuration. We propose that, Type II canal configuration might be a coincidence along with the Type I dens invaginatus and this morphological anomaly may be the possible reason for nonvitality of the tooth. The lack of any history or clinical findings of trauma including minute cracks or fracture lines on incisors rules out the possibility of this being a case of trauma-induced pulp stones or diffuse calcifications. Moreover, traumatic events rarely reproduce uniform clinical or radiological manifestations on all the anteriors. The expression of cystic fluid only through orifice of lateral incisor when the access canals for both central and lateral incisor were kept open suggests that the focus of infection was the lateral incisor. The nonvitality of the central incisor could be secondary to the chronic periapical infection from the lateral incisor.

CONCLUSION

Rarity of complex canal anatomy in maxillary anteriors should not give way to a perception of ignorance. Diligence of operator enhanced with modern diagnostic aids helps to accomplish success in such unique cases, which poses challenges in diagnosis and treatment execution.