One hundred and ï¿ fty-one mandibular second molars scheduled for root-canal treatment were examined over a 1-year period in the Endodontic Department, King Fahad National Guard Hospital, Riyadh, Saudi Arabia. The incidence of C-shaped canalswas revealedfollowing radiographic and clinical examination. Three preoperative radiographswere takenat a constant target-ï¿ lmdistance and angulation by utilizing the extension cone paralleling device (Rinn Corp., Elgin, III, USA): onewith a908 angulation to the tooth ina buccolingual direction and another two at a mesial and distal angulation of approximately 208 to allow better visualization of the buccolingual anatomy.The radiographs were examined on a viewer using a peripheral block and a 6_magnifying lens.The numberand the positionof root canalswere noted. Three postoperative radiographs using the same exposure geometry were taken to conï¿ rm canal configuration.
Clinical examination of the pulp chamber and canal orifices was carried out and root canals were investigated with size 10 K-ï¿ les (Kerr Co., Romulus, MI, USA); radiographs were taken to conï¿ rm canal morphology. Once C-shaped anatomy was recognized, teeth were categorizedusingamodiï¿ cationof anexisting classiï¿ cation (Melton et al.1991).

• Category I: continuous C-shaped canal running from the pulp chamber to the apex (Fig. 2).
  
• Category II:‘semicolon’ (;) shaped orifice inwhich dentine separated a main C-shaped canal from onemesial distinct canal (Fig. 3).
  
• Category III: subdivision I, C-shaped orifice inthe coronal third that divided into two or more discrete and separate canals that joined apically (Fig. 4); subdivision II, C-shaped orifice in the coronal third that divided into two or more discrete and separate canals in the mid-root to the apex (Fig. 5); and subdivision III, C-shaped orifice that divided into two or more discrete and separate canals in the coronal third to the apex (Fig. 6).

Figure 2. Category I: (A) preoperative radiograph of the mandibular second molar showing fused roots and (B) completed root filling using lateral condensation of gutta-percha showing true C-shaped canal.



Figure 3. Category II: (A) preoperative radiograph showing a radicular fusion, a large distal canal, a narrow mesial canal, and a blurred image of a third canal in centre; (B) postoperative radiograph. Note the presence of dentine separating a mesial canal from the rest of the C-shaped canal.



Figure 4. (A) Preoperative radiograph of a mandibular second molar and (B) postoperative radiograph. Note the apical fusion of the three canals.



Figure 5. (A) Preoperative radiograph of a mandibular second molar and (B) postoperative radiograph. Note the main C-shaped canal splits near themid-root into three canals.



Figure 6. (A) Preoperative radiograph of a mandibular second molar and (B) postopertive radiograph. Note the main C-shaped canal splits in the coronal third into three canals.