Fig. 2

Comparison of manual and electric toothbrushes. a The reduction rate of plaque after manual or electric tooth brushing. There was no significant difference between the two (P = 0.679, Wilcoxon signed-rank test). b By comparing the two techniques, we subtracted the efficiency of manual and electric toothbrushes for each student. The differences in the frequency of toothbrush efficiency are also depicted. The green panel shows the efficiency and frequency of students whose manual toothbrushing overwhelmed electric tooth brushing (n = 82). The blue panel shows the students whose electric toothbrushing overwhelmed manual tooth brushing (n = 90). Only 4 students exhibited equal efficiency. c 49 of 176 students (27.27%) had an apparent difference (more than 10% of plaque removal) between manual and electric tooth brushing