Dens invaginatus is a developmental malformation resulting from invagination of the tooth crown or root before calcification has occurred. The presumed aetiology of this phenomenon has been related either to focal growth retardation or focal growth stimulation, or to localized external pressure in certain areas of the tooth bud (Shafer et al . 1983). The condition may occur in any deciduous or permanent tooth. The permanent maxillary incisors are the most frequently involved teeth (Bimstein & Shteyer 1976). Radiographically this anomaly demonstrates a radiopaque invagination, equal in density to enamel, extending from the cingulum into the root canal (Gotoh et al . 1979). The defects may vary in size and shape from a loop-like, pearshaped or slightly radiolucent structure to a severe form resembling a ‘tooth within a tooth’. The classification of Oehlers (1957) is as follows:

 - Type 1; an enamel invagination in the crown only.
 - Type 2; an enamel-lined invagination that invades the root but remains confined within it as a blind sac, and may communicate with the dental pulp.
 - Type 3; an invagination that extends from the crown to the apex.

An early diagnosis of such malformations is crucial. Due to abnormal anatomical configuration, an invaginated tooth presents technical difficulties in its clinical management. Various techniques for treating dens invaginatus have been reported, including conservative restorative treatment (de Sousa & Bramante 1998), non-surgical root canal treatment (Hosey & Bedi 1996), endodontic surgery (Bolanos et al . 1988), intentional replantation (Lindner et al . 1995) and extraction. The purpose of the present article is to describe a case of apical periodontitis associated with a tooth containing a dens invaginatus that healed successfully after non-surgical root canal treatment.

A 10-year-old girl was referred by her general dental practitioner because of pain and swelling from her maxillary right lateral incisor. The patient described an episode of recent severe throbbing pain over the past 2 days; there was no previous history of any signs or symptoms. The medical history was non-contributory. Clinical examination revealed that there was a swelling buccal to the lateral incisor (Fig. 1). The tooth was caries free but had an enamel projection in the centre of its lingual surface (Fig. 2). The gingival probing depths were within normal limits. The tooth was sensitive to percussion and failed to respond to electric pulp sensitivity testing. The adjacent teeth all responded within normal limits to percussion and sensitivity testing. A periapical radiograph demonstrated a radiolucent lesion in the mesial aspect of the apical third of the right lateral incisor (Fig. 3). A clinical diagnosis was established of dens invaginatus (Oehlers Type 2), necrotic pulp and acute apical abscess. Following isolation of the tooth with a rubber dam, the pulp chamber was opened and the invagination orifice located. When the invagination orifice was enlarged, the primary root canal was discovered in a more lingual position (Fig. 4). A radiograph with files in the root canals was obtained (Fig. 5).

Figure 1. Preoperative view of maxillary lateral incisor showing localized swelling.


Figure 2. Preoperative palatal view of maxillary lateral incisor. Note the large enamel projection.


Figure 3. Preoperative radiograph of maxillary lateral incisor showing dens invaginatus with periapical radiolucency.


Figure 4. Access opening demonstrating two distinct canal orifices.


Figure 5. K-files in both canals.


Figure 6. Radiograph immediately after obturation of primary root canal. No communication with invagination is evident.


Figure 7. Two-year follow-up radiograph of maxillary lateral incisor. Radiograph reveals a reduction in size of the radiolucent area.

The working lengths were established and recorded. The radiograph revealed a region of root resorption, with a lateral root perforation on the mesial surface. The invagination appeared to be calcified. There did not appear to be any communication between the primary root canal and the invagination. The canal system was debrided thoroughly and prepared by the step-back technique to a size 40. Copious irrigation with 2.6% sodium hypochlorite solution was used throughout the procedure. After drying the root canals with paper points, a cotton pellet was placed in the pulp chamber and the tooth was temporarily sealed with Cavit (ESPE, Seefeld, Germany). One week later, the patient returned without symptoms and the swelling had disappeared. The invagination was obturated by lateral condensation of gutta-percha and zinc oxide-eugenol sealer (Canals, Showa Yakuhin, Tokyo, Japan). The primary root canal was dried and filled with calcium hydroxide paste. Cotton wool and Cavit were placed in the access opening. The patient returned after 3 months, and the primary root canal was obturated using an injection-moulded thermoplasticized gutta-percha delivery system (Obtura II, Obtura Corp., Fenton, MO, USA) and zinc oxide-eugenol sealer. A postoperative radiograph was taken (Fig. 6). The patient was recalled periodically and healing was uneventful. The recall radiograph at 2 years showed osseous repair; the patient remained asymptomatic (Fig. 7).

Discussion.
Clinicians should be aware of the incidence and methods for treating dens invaginatus . Failure to locate, debride and obturate complex root canal spaces will lead to failure in some cases. According to the classification of Oehlers (1957) the present case was a type 2. In this type of dens invaginatus , the invagination remains confined within the root as a blind sac, which may communicate with the pulp. However, in this case the invagination did not appear to communicate with the pulp and clinical exploration during root canal treatment corroborated this assumption. Therefore, the aetiology of the periapical pathosis in this case was due to the infected primary root canal. However, it is not known how long the primary root canal had been infected prior to the patient developing symptoms. Mechanical debridement of the primary root canal was difficult, but the combination of chemomechanical instrumentation and the use of calcium hydroxide were sufficient without resorting to surgery. As calcium hydroxide has been reported to successfully eliminate bacteria (Byström et al . 1985) and stimulate hard tissue repair (Heithersay 1975), it was decided to treat the primary root canal with this medicament before obturating the root canal with gutta-percha. The use of a warm gutta-percha technique helped to obturate the root canal system, as it was possible to compact the softened material into the major irregularities within the root canal system (Budd et al . 1991, Gutmann 1993).

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