Prevalence of 3-rooted first permanent molars among a Shanghai Chinese population.

Objectives: This study aimed to assess the prevalence of 3-rooted mandibular first molars among a Shanghai Chinese population by using periapical radiographs.

Methods: A total of 510 patients possessing both mandibular first molars were selected. The radiographs of these cases were evaluated under optimal conditions using double magnifying glasses. The incidence of 3-rooted mandibular first molars and the correlation between occurrences in males and females and between the left and right sides were recorded and analyzed. A total of 1020 mandibular first molars were evaluated.

Results: A total of 165 patients were found to have a 3-rooted mandibular first molar: 92 males and 73 females (P = .106). The overall incidence of patients with 3-rooted mandibular first molars was 32.35%. Of all the patients with 3-rooted molars, 67.27% (111/165) of cases occurred bilaterally. The incidence of teeth showing an extra root was 27.06%. The occurrence of such permanent 3-rooted mandibular first molars also did not differ significantly between the right side (n = 142, 13.92%) and the left side (n = 134, 13.14%; P = .573).

Conclusions: The prevalence and bilateral incidence of 3-rooted mandibular first molars among the Shanghai Chinese population was high and such variation varied among Chinese populations living in different areas.