The morphology of the maxillary second premolar had been reviewed extensively in the literature. The prevalence of one, two or three canals has been reported in vitro and in vivo.1-4 The incidence of two root canals in the maxillary second premolar has been reported to vary between 28 percent and 58.6 percent, whereas the incidence of three root canals has been reported to be much lower at 1.1 percent [Table 1].
Table 1. Percentage of three canal led maxillary second premolar
                                                               No. of
Author                                                      teeth         %
Pineda &Kuttler1                                        282           0
Green-1                                                       50            0
Vertucci.Seelig&Cillis3                               200           1
Bellizi & Hartwell4                                     630          1.1
Radrographrcally, it is easier to detect teeth with extra roots than teeth with the usual number of roots and extra canals.5 The possibility of a third canal in the upper premolars may be suspected during access opening when the pulp chamber deviates from its classic alignment in the buccal-palatal relationship. Bellizzi and Hartwell6 recog­ nized the presence of the three-rooted premolar after endodontic therapy, when persistent post­ operative pain had to be evaluated.
The purpose of this article is to report a case of a maxillary second premolar with three root canals.
Case Report
A 25-year-old male was referred to the Endodon­ tic Division at King Saud University College of Dentistry's undergraduate clinic for evaluation and completion of root canal therapy of the maxillary left second premolar. Medical history was noncon-tributory. The clinical examination of the tooth gave a positive response to percussion and palpa­ tion. The tooth was restored with amalgam. Radiographic examination showed only the palatal canal obturated [Fig. 1j. The patient's record was reviewed. Three canals had previously been located and partially instrumented. After rubber dam isolation, the tooth and operating field were disinfected with 30 percent hydrogen peroxide fol­ lowed by 5 percent tincture of iodine. The tooth and operating field were redisinfected after estab­ lishing the access opening. The mesiobuccal (MB) and distobuccal (DB) canals were located [Fig. 2] and the working length of both canals were checked radiographically [Fig, 3]. The canals were instrumented, irrigated with 1 percent sodium hypochlorite and dried with sterile paper points. A 2 percent solution of potassium iodide was placed into the pulp space between the visits. At the obtu­ ration visit, the tooth was asymptomatic, the operating field was isolated and disinfected. The canals were irrigated with sodium hypochlorite and dried with sterile paper points. Obturation of the MB and DB canals were completed using lat- eral condensation of gutta percha and AH26 sealer cement. Access opening was sealed with para-post and amalgam restoration, the rubber dam was removed, and a postoperative radiograph was taken [Fig. 4].

Incomplete obturation of the canal space was found to be the highest cause among those for root canal therapy failures.7 If the canal is originally cleaned but incompletely filled, tissue fluid break­ down products from the area can cause chronic inflammatory response in the periapical tissue. With this in mind, a thorough knowledge of pulp space morphology is essential when practicing endodontics. This will help to reduce endodontic failure caused by incomplete obturation.
Sieraski et al8 gave a general guideline for the identification of three rooted maxillary premolars using radiographs. He stated that, most likely, the tooth has three roots if the mesio-distal width of the mid-root image appears equal to or greater than the mesio-distal width of the crown image. A similar finding was observed in this case report.
Finally, when performing root canal therapy, the operator must always be aware and prepared for unexpected root canal morphology. Careful radiographic examination may lead to the identifi­ cation of additional roots or canals. In addition, careful examination of the pulp chamber will help in locating the orifice of additional canals not visi­ ble radiographically.