A retrospective study of endodontically treated mandibular first molars in a Chinese population.

The purpose of this investigation was to study the prevalence of three roots and four root canals in the mandibular first molars of a Chinese population. A total of 832 cases of mandibular first molars that had received root canal treatment clinically were examined by reviewing the clinical records and radiographs. The results showed that: (a) Mandibular first molars with four root canals occur at a frequency of 31.5%. (b) More than two-thirds (68.3%) of the above cases had the fourth canal arising from the third root, an extradistal root. (c) The bilateral occurrence of this extradistal root in mandibular first molars was 67%. In conclusion, the occurrence of four root canals in mandibular first molars among Chinese people was not unusual.