Max first premolar: While it is uncommon to see 2 canals in the first max PM, it is even rarer to see 3 canals.
According to Vertucci, 1st max PM will have 3 canals 6% of the time. In the 2nd max PM, it will have 3 canals 1% of the time.
Here, patient presented to clinic complaining of pain on biting. Clinical diagnosis was root canal treated tooth with chronic symptomatic apical periodontis. Non-surgical retreatment was recommended and completed. Patient was asymptomatic at completion of appointment.
Mandibular PM. As for mandibular PM, the incidence of 3 canals is even rarer. According to Baisden, it happens about 0.5% of the time.
Here we have a case of necrotic pulp with chronic suppurative apical abscess. In the pre-op radiograph the sinus tract was traced, but did not conclusively confirm the origin of the sinus tract. RCT was recommended and completed.
Notice, here one canal branches into three; a 1–3 system.