An internationally recognized system of tooth numbering in which teeth in each quadrant are identified by numbers I through 8. A second number indicates the quadrant. Quadrant 1 is the maxillary right quadrant, quadrant 2 is the maxillary left quadrant, quadrant 3 is the mandibular left quadrant, and quadrant 4 is the mandibular right quadrant. Tooth number 13, e.g., indicates the maxillary right quadrant and the canine tooth.