A three-rooted mandibular second premolar.

If an endodontic problem is diagnosed in a mandibular premolar, and root canal therapy is provided, it must be considered that second and third canals might exist. Although the existence of a third canal would be rare, a thorough evaluation may help to prevent future complications. In the case presented here, failure to recognize a third canal might have resulted in incomplete instrumentation and canal obturation, and endodontic failure. Variations in root canal morphology and the number of canals might not have been detected even during close inspection of the pulp chamber floor. Therefore, the dentist must have a thorough knowledge of root canal morphology and its variations.