Objective: This study was to evaluate the number and the C-shaped root canal morphology in the mandibular second molars of the Vietnamese. Subject and methods: The authors collected the mandibular second molar extracted from Vietnamese patients. The teeth after spit are cleaned out by soaking in NaOCI solution of 5.25% for 24 hours, then fixed In a 10% formol solution. Selection of C-shaped teeth in the study. Perform demineralisation, make transparent teeth, then pump Indian ink. Observe and record the number of canals and canal morphology according to Vertucci classification under scanning electron microscope. Piethods: Preclinical study. Results: The C-type mandibular second molars consisted of two canals (59.4%), one canal, three canal and four canal respectively 31.2%
6.3% and 3.1% respedively. The most common type of canal was type I (31.2%), followed by type III (25%), type V (18.8%), type IV (15.6%), Type VIII (6.3%), Type II (3.1%) and no teeth with type VI and VII canals, Conclusion: The C-shaped root mandibular second molars in Vietnamese have a complex and diverse number of canals.