Y. Nahmias & M. E. Rampado
Department of Endodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.

Introduction.
Morphological aberrations in teeth present challenges to root-canal treatment. In such cases, an awareness of the possible anatomical variations is essential to localize and successfully treat the entire root-canal system (Libfeld et al. 1986). Clinical and radiographic examination as well as a diagnosis of the morphological aberration as gemination or fusion help to gain insight into the root-canal anatomy.
Gemination has been described as a malformation of a single tooth bud (Pindborg 1970). It results in the formation of two (or more) identical crowns with a radiographic appearance of one single root and canal (Itkin & Barr 1975). Fusion has been defined as a union of two separate tooth buds at some stage in their development with two root canals contained in one or two roots (Tannenbaum & Alling 1963). Gemination results in an arch containing the normal complement of teeth, whereas in fusion, there will be one tooth less (Spatafore 1992). The number of teeth in the arch would remain normal in cases where fusion has occurred with a supernumerary tooth.
The cause of these morphological variations is unknown, although they are believed to have a hereditary tendency (Pindborg 1970, Shafer et al. 1983). Several authors (Clayton 1956, Brook & Winter 1970, Blaney et al. 1982) have reported that these anomalies occur most often in anterior teeth with the incidence in the permanent dentition (<0.8%) significantly lower than that in the primary dentition (0.1–3.7%). Although fused and geminated posterior permanent teeth are considered to be rare, Stabholz & Friedman (1983) reported a case requiring root-canal treatment. The aim of this article was to present a case of suspected gemination of a permanent maxillary first premolar with a trifid crown that required root-canal treatment.

Clinical history.
A 17-year-old female patient was referred by her general dentist for root-canal treatment of tooth 24. Her medical history was noncontributory. The patient’s chief complaint was a throbbing ache with localized cold and percussion sensitivity that had persisted for 1 week. The dentist had prescribed antibiotics which had helped to alleviate the discomfort. Clinical examination revealed the normal complement of teeth. The maxillary left first premolar had three intact crowns with sealants placed on the occlusal surfaces (Fig. 1). For charting purposes, each crown was named accordingly as the mesial, distal or palatal crown. The mesial crown displayed a morphology typical of the maxillary left first premolar. The distal crown was atypical in size and characteristics with the palatal crown being most atypical. Upon palpation, there was pain and discomfort in the apical region. Cold testing with an ice stick and vertical percussion were positive, and reproduced the patients chief complaint. All other teeth were unremarkable in shape. Adjacent teeth responded within normal limits to testing. Radiographic examination revealed that the crowns joined to give the appearance of a single root at the cementoenamel junction (Fig. 2). The appearance of more than one distinct lamina dura in the mid-root aspect indicated a C-form or the possibility of branching into more than one root. No periapical radiolucency was detected. A diagnosis of irreversible pulpitis with acute apical periodontitis was made.

Figure 1. Preoperative photograph of the trifid crown of tooth 24: mesial (M), distal (D) and palatal (P) crown.



Figure 2. Preoperative radiograph showing trifid crowns joining at the cementoenamel junction.



Figure 3. Photograph showing three separate access openings and four no. 15 files.

Teeth 24 and 25 were isolated with rubber dam by placing the clamp on tooth 25. Three access openings were made, one into each crown (Fig. 3). The mesial crown had two canals, the distal and the palatal one each. Length was established with an electronic apex locator (Ultima EZ, Amadent, Cherry Hill, NJ, USA) and confirmed radiographically (Fig. 4). During treatment, the distal and the palatal canals joined in the coronal third to form a main canal and the palatal canal of the mesial crown also joined this main canal in the apical third. The canals were prepared manually with a balanced force crown-down technique using Flexofiles (Dentsply, Tulsa, OK, USA). Sodium hypochlorite solution (5%) was used for irrigation. The canals were obturated at the same appointment with Pulp Canal Sealer (Kerr Corporation, Orange, CA, USA) and the warm vertical condensation using the System B (Analytic Technology, Orange, CA, USA) heat tip and the Obtura II (Spartan, Fenton, MI, USA) to backfill. TERM (L.D. Caulk, Milford, DE, USA) was used to place three separate temporary restorations. A radiograph was taken immediately after completion (Fig. 5). The patient was referred back to her dentist for permanent restorations. In a telephone conversation, the patient reported complete alleviation of symptoms after 1 week. The tooth remained asymptomatic and unremarkable upon clinical and radiographic examination approximately 6 months following treatment, as related by the general practitioner.

Figure 4. Trial file radiograph showing one distinct canal and the merging of three canals into one common canal.



Figure 5. Radiograph after obturation of the root canals.

Discussion.
Root-canal treatment of fused or geminated teeth has been described by various authors (Tagger 1975, Libfeld et al. 1986, Wong 1991). A literature review failed to reveal treatment of a trifid crown permanent maxillary first premolar. Although more than one separate rootcanal lends support to the diagnosis of fusion, the diagnosis of gemination was based on the clinical examination and finding that three of the canals joined to form a common main canal. The formation of this tooth within the normal complement of teeth and the similar mirror-image effect of the three crowns supports this diagnosis. Gemination occurs because of a partial division of a single tooth bud through invagination, resulting in completely or incompletely separated crowns (Pindborg 1970). In this case, the aetiology of this abnormal tooth development is unknown. Consultation with the family members and the referring dentist revealed no hereditary or causal link.
The tooth exhibited percussion and thermal sensitivity in addition to pain on palpation, symptoms indicative of an irreversibly inflamed pulp with extension of inflammatory changes to the periapex. As the tooth was caries-free and no history of trauma was reported, it is likely that the unusual anatomy lead to the irreversible condition of the tooth and the patients symptoms. Though not detected clinically, enamel deficiencies may be present in the developmental grooves between the three crowns. This would allow bacteria to gain access to the pulp chamber in a similar manner to that which occurs in dens invaginatus.
Management of the case required careful consideration of the possible morphological aberrations. Clinical and radiographic evaluation indicated that access into each of the crowns was necessary. The complexities of the root-canal systems could then be addressed during treatment. This case illustrates that, despite the unusual morphology and the lack of a comparative case in the literature, the use of sound endodontic principles resulted in successful treatment.

References.

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Brook AH, Winter GB (1970) A retrospective study of 'geminated' and 'fused' teeth in children. British Dental Journal 129, 123-30.
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