Abstract: Objective To investigate the types of mesial middle root canals (MM) and correlate the clinical incidence of mesial middle root canals of mandibular first molars with variables of gender, age, tooth type. Methods 12 mature permanent mandibular first molars with mesial middle root canals from August 2014 to August 2015 were included in the analysis. Types of MM according to Vertucci or Pomeranz, tooth type, gender, and age were recorded. Results Of the 12 mandibular first molars with MM, most of them were confluent in patient >30 years old while independent in patient <30 years. There was no difference in gender. However, significant difference was observed in tooth type-occurrence on right side was more than that on the left side. Conclusion Gender and tooth type might be the key factors, which determine the existence of MM.

Key words: mandibular first molar, mesial middle canal, root canal therapy