ABSTRACT
The aim of this study was to clinically investigate the incidence of a fourth canal in maxillary and mandibular first molars in a group of Jordanians while carrying out routine endodontic practice without using any magnification or special lighting conditions. Three hundred ninety nine patients were referred to the conservative clinic at Princess Aysha Bint Al-Hussein Medical Complex for endodontic treatment of maxillary or mandibular first molars from November 2008 till May 2009. Preoperative radiographs were taken for evaluation. The teeth included in the study were both clinically and radiographically examined for the number of root canals. A total of 399 patients [216 female and 183 male] were treated at the conservative clinic. The mean age of patients was 28.23 years, ranging from 13.0 to 66.0 years. Out of 399 teeth treated endodontically, 195 [48.9%] were maxillary first molars and 204 [51.1%] were mandibular first molars. Forty five teeth [23.08%] out of the 195 treated maxillary first molars had second canal [Mb2] in the mesiobuccal root; all the distobuccal and palatal roots had a single canal. Regarding the mandibular first molars out of the 204 treated teeth, 99 teeth [48.5%] had 4 canals; two mesial and two distal canals.A fourth canal was found in about 23% of maxillary first molars and in about 49% of mandibular first molars. There is no consistency in the incidence of extra canals. This may be due many variations including the study design, the method of canal identification and the racial variations